high speed camera flash

High speed camera flash

Fast imaging system

Bachelor’s thesis

Automation Engineering

Valkeakoski, spring 2015

Michiel Keeris & Geoffrey Vander Cruyssen

Clarification of signature

ABSTRACT

Valkeakoski

Degree programme in Automation Engineering

Author Michiel Keeris & Geoffrey Vander Cruyssen Year 2015

Subject of Bachelor’s thesis High speed camera flash

ABSTRACT

This thesis mainly focuses on the design of a fast imaging system used to image fast

flowing particles in a controlled environment, specifically the high power small pulse

flash needed to accomplish this system and the synchronization with the diaphragm of

the camera used to take the image. The project was an assignment of Physics teacher

Raine Lehto. The objective was to make a fast imaging system to check the quality of

recycled paper fibre made in a paper factory in the neighbourhood. The primary goal was

the design of the flash. This flash has to be of high power and very short in lighting time

in order to produce a very clear picture of moving paper, as a short flash gives the im-

pression that the paper is standing still while the paper is actually moving through the

production machine. We also had to make sure this flash was in full synchronization with

the camera taking the picture to provide the clearest possible image.

The thesis primarily used electronics theory. The flash was designed from zero with elec-

tronics. The main concerns were finding the appropriate power LED, components fast

enough to meet the demands, a stable high-power power supply and synchronizing the

flash to happen when the shutter of the camera is open.

Research was done about usable schematics of existing systems, and appropriate compo-

nents that are accurate enough to accomplish this system. During this research, experi-

ments were conducted with components and circuits to achieve the desired result as close

as possible. Once the best circuits and components were found, the thesis moved over to

building prototypes on a PCB (Printed Circuit Board) as this is as close to a final product

as possible.

This project is expected to include a lot of trial and error in terms of experiments, allowing

to adjust the circuits and components to maximum efficiency. The most complicated part

was to design the flash as close as possible to the demands, as it had to be very accurate

and externally controllable. The second part was the synchronization with the camera.

Keywords Camera, High-speed, Flash, electronics

Pages 37 p. + appendices XX p.

ACKNOWLEDGMENTS

After a period of three months we have arrived at the end of this thesis, with

the writing of this acknowledgment we end the final chapter of our bachelor

study. We are both forever grateful to have had the chance to study and

work here at the University of Applied Sciences HAMK in Finland. We

have had happy moments here but also quite intensive ones.

Naturally we want to thank a few people who have helped us along the way

of this thesis. First of we want to thank Raine Lehto for giving us the as-

signment for this thesis and putting his confidence in us while mentoring us

along the way.

Secondly we would like to thank some people in Belgium for which without

their help we wouldn’t be here, as there are Patrick Debbaut, Dirk Thomas

and Caroline Van der Veer. They have worked so hard behind the curtains

just to get us to this place and even after we were here they kept on helping.

We also would like to show our gratitude to Osmo Leiniäinen for the use of

his sometimes messy laboratory and the help with ordering components.

Last but not least we would like to thank all our friends we made her in

Valkeakoski because they encouraged us to keep on working on this thesis

and especially Alexandra, who kept on sending us a message each morning

for the last few weeks to motivate and to bring this thesis to a good end.

Michiel Keeris & Geoffrey Vander Cruyssen

Valkeakoski, Finland, 20 may 2015

LIST OF FIGURES

Figure 1: Time trace of light emission as detected by a photodiode (upper trace) for a

high-power LED (left) and a conventional xenon flash lamp (right) in response to a trigger

pulse (lower trace). (Willert, 2010) .................................................................................. 4

Figure 2: Block Diagram of the designed flash ............................................................. 5 Figure 3: Hot Shoe PC Sync connection foot (amazon.com) ........................................ 6 Figure 4: The 555 IC as a monostable multivibrator. (Digital fundamentals, Floyd) ... 7 Figure 5: Internal schematic of the monostable multivibrator IC (Texas Instruments,

2004) 7 Figure 6: Monostable multivibrator INPUT/OUTPUT timing diagram (Texas

Instruments, 2004) ............................................................................................................ 8 Figure 7: Output Pulse Duration vs External Timing Capacitance graph (Texas

Instruments, 2004) ............................................................................................................ 9

Figure 8: Construction of the RC timing network ......................................................... 9 Figure 9: Overview of the monostable multivibrator network .................................... 10 Figure 10: Rise-time and delay-time between input signal and output signal of the

74LVC1G123 monostable multivibrator. ....................................................................... 11 Figure 11: Minimum pulse width generated by the 74LVC1G123 monostable

multivibrator. .................................................................................................................. 11

Figure 12: Maximum pulse width (1µs) generated by the 74LVC1G123 monostable

multivibrator. .................................................................................................................. 12 Figure 13: Pulse width of 500ns generated by the 74LVC1G123 monostable

multivibrator. .................................................................................................................. 12 Figure 14: Overview of the totem-pole ...................................................................... 13

Figure 15: powering up the totem-pole circuit and pulling MOSFET gate to the ground

14 Figure 16: Positive pulse, MOSFET is forced to open .............................................. 15 Figure 17: totem-pole Pulse has ended ...................................................................... 15 Figure 18: Signal on the MOSFET base on channel 1 (upper trace) and output

monostable multivibrator on channel 2 (lower trace). .................................................... 16 Figure 19: Signal on the MOSFET base on channel 1 and output monostable

multivibrator on channel 2 with channel overlap. .......................................................... 16 Figure 20: Rising edge on input B of the monostable multivibrator on channel 1 (upper

trace) and signal on the MOSFET base on channel 2 (lower trace). .............................. 17 Figure 21: LED driver circuit ..................................................................................... 18 Figure 22: Maximum pulse possible: channel 1 is the voltage measured at MOSFET

drain, channel 2 is the voltage measured at MOSFET gate............................................ 20 Figure 23: Minimum pulse possible: channel 1 is the voltage measured at MOSFET

drain, channel 2 is the voltage measured at MOSFET gate............................................ 20 Figure 24: Pulse to short, LED barely lights up: channel 1 is the voltage measured at

MOSFET drain, channel 2 is the voltage measured at MOSFET gate. .......................... 21 Figure 25: Channel 1 is the voltage measured over R7, channel 2 is the voltage

measured at MOSFET gate............................................................................................. 21

Figure 26: Channel 1 is the voltage measured over R7 with added snubber of 220nF,

channel 2 is the voltage measured at MOSFET gate. ..................................................... 22 Figure 27: Luminosity of high-power LEDs driven with 1 kHz current pulses of τ p =

1μs duration. 23

Figure 28: LZ4-40CW08-0065 on a MCPCB (MOUSER.com) ............................... 24 Figure 29: complete schematic of the designed circuit .............................................. 26

Figure 30: PCB design schematic .............................................................................. 27 Figure 31: Component layout of the designed PCB .................................................. 28 Figure 32: Component layout of totem pole configuration ........................................ 29

Figure 33: Trace layout of the PCB ........................................................................... 29 Figure 34: PCB divided in parts in terms of current .................................................. 30

Figure 35: layout of a SLR (Roberts, 2013) ............................................................... 32

Figure 36: Principal circuit diagram of a PC power supply (Hans Haase) ................ 33

LIST OF TABLES

Table 1: Logic table of the monostable multivibrator (Texas Instruments, 2004) ....... 7 Table 2: LZ4-40CW08-0065 specifications ............................................................... 24 Table 3: LZ1-10CW02-0065 specifications ............................................................... 25 Table 4: circuit component list ................................................................................... 25

CONTENTS

1 INTRODUCTION ....................................................................................................... 1

2 ASSIGNMENT ........................................................................................................... 2

3 CAMERA FLASH ...................................................................................................... 2

3.1 Flash and its use in photography ......................................................................... 2 3.2 Flash synchronization .......................................................................................... 3 3.3 Types of high-speed flash ................................................................................... 3

3.4 LED versus ARC lamps ...................................................................................... 3 3.5 Flash in our project .............................................................................................. 4

4 COMPONENTS .......................................................................................................... 4

4.1 Block Diagram .................................................................................................... 5 4.2 Hot shoe Camera (PC sync) ................................................................................ 5 4.3 Monostable multivibrator .................................................................................... 6

4.3.1 Calculation of the pulse width ................................................................. 8

4.3.2 Measurements on the monostable multivibrator ................................... 10 4.4 Totem-pole ........................................................................................................ 12

4.4.1 Construction of the totem-pole .............................................................. 12 4.4.2 Measurements on the totem-pole ........................................................... 16

4.5 LED DRIVER ................................................................................................... 17 4.5.1 Construction of the LED driver ............................................................. 17

4.5.2 Measurements on the LED driver .......................................................... 19 4.6 LED ................................................................................................................... 22

4.6.1 LED in overdrive ................................................................................... 22

4.6.2 Chosen LEDs ......................................................................................... 23 4.6.3 LZ4-40CW08-0065 ............................................................................... 24

4.6.4 LZ1-10CW02-0065 ............................................................................... 24

4.7 Complete schematic of the high speed flash ..................................................... 25

5 PRINTED CIRCUIT BOARD .................................................................................. 27

6 DSLR CAMERA ....................................................................................................... 31

7 POWER SUPPLY ..................................................................................................... 32

7.1 Computer Power Supply Unit ........................................................................... 32 7.2 Power Factor (PF) and Power Factor Correction (PFC) ................................... 33 7.3 Power supply calculation .................................................................................. 34

8 CONCLUSION ......................................................................................................... 34

SOURCES ...................................................................................................................... 36

Appendix 1 Datasheets


1

1 INTRODUCTION

The use of high speed image capturing is in use all over the world. It is used

in a variety of sectors, but all with the same purpose: taking very clear and

precise images of extremely fast moving objects. With these images you

can check or image things and objects that cannot be measured with regular

video recording or photographing. This is done for various reason and ap-

plications such as monitoring and controlling industrial machines, in exper-

iments with for example fast travelling bullets or projectiles, chemical reac-

tions, quality control of press-work and printed matter and many others.

One of the major problems is that most camera systems are very expensive

and bulky. It is possible to make such a fast imaging system with mid-high

range SLR cameras. There is one problem however, when capturing images

of very fast moving objects, constant lighting is not an option as images will

become blurry because of the shutter time on the used cameras. This is

where this project comes in handy. The general intention was to make a

flash that would be so short in duration that it seems as if the moving parti-

cles or objects were still for the duration of the flash. This could be achieved

by creating a flash that lasts for only a couple of hundred nanoseconds. This

is where regular flash systems fall short. Their flash duration is considerably

longer than needed to produce a clear, still image of fast moving objects. As

these typical flash systems mostly use xenon flashes, we used LEDs in order

to achieve this very short flash timing.

This thesis handles the calculations and design of this high-speed short

pulse flash. The project was initiated by research on this subject, and selec-

tion of the correct lighting technology. Once the best technology was found,

the best way to get an overview was to make a block diagram of the different

sections that were needed to make a complete schematic. As the decision

was made on what sections the system needed, the research became more

precise and accurate and fast components will be sought after. As pieces of

the schematic were completed, these were put together in a final schematic

of the entire device. Final calculations were made to correctly connect one

part to another and calculate all the relevant currents and voltages. When all

the theoretical work was complete and accurate, the project went over to the

practical design of the system. This included ordering components and de-

signing a PCB (Printed Circuit Board). As the components arrived and the

PCB was etched, the components were soldered onto the PCB and the test-

ing phase was put into motion. In the testing phase the first thing to check

was the functionality of the device. For accurate measurements, the proper

measuring equipment (an oscilloscope) was required as a flash of this short

a duration is almost impossible to see. Once the device functioned as in-

tended, all relevant currents and voltages were measured in order to com-

pare them with the theoretical work and verify that everything is working

the way it should. During this entire practical process, small changes were

made in order to improve the quality of the device. This thesis will handle

the theoretical aspect of the device, followed by the practical measurements.


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2 ASSIGNMENT

As the design of an appropriate illumination flash for the imaging system is

a complex matter on its own, project supervisor Raine Lehto decided to out-

source the project to other automation engineering students for a separate

thesis. This system has to be very fast and accurate. As most of the flashes

available on the market are either too expensive or not fast enough, the ob-

jective of this thesis was to design a relatively low cost, fast and accurate

imaging flash system.

In order to obtain the image quality needed, the flash has to be very short in

duration, somewhere between a few 100 nanoseconds and 1-2 microsec-

onds. This flash duration had to be adjustable in order to customize the sys-

tem to the needs of the user and to adjust the system to the environment and

equipment. A synchronization between the imaging system, i.e. the camera,

and the illumination system, i.e. the flash, was also needed. This could be

accomplished by designing the system in such a way that the flash could be

moved based on time in relation to the trigger pulse. This basically means

there had to be an option to slow the flash down to a level where the flash

takes place on the exact moment it has to take place, i.e. the opening of the

shutter of the camera.

Another demand that had to be met was the illumination. The flash had to

be bright enough for a clear image with proper lighting, allowing the camera

to take in as much light as possible. This basically meant that the brighter

the light source is, the better. The suggested component was a high power

LED, a suggestion that was followed. When selecting the appropriate LEDs,

we chose the component with maximum brightness for the given variables

and parameters. This LED would be used light up the background of the

image instead of a frontal flash. To evenly distribute the light a transparent

plate would be used, making sure the entire background has the same level

of lighting across the entire surface. This was the reason for always choos-

ing maximum brightness where possible.

3 CAMERA FLASH

3.1 Flash and its use in photography

In this context, a flash is a device used to produce a flash of artificial light

at a specific colour temperature (around 6000K). This is used to illuminate

a dark area, capture fast moving objects or change the overall quality of

light in the scene. Early flash units were made out of single-use flashbulbs

and flammable powders, but nowadays all flashes are electronic. Most of

the time the flashes are programmable in duration and intensity. Colour tem-

perature depends on the flash, but is also very important. Flash duration is

only really important in applications such as sports photography and deter-

mines the ability to ‘freeze’ moving subjects.

Flash intensity is really what it says it is; the intensity of the flash, resulting

in more or less lighting. The lumen is the SI derived unit of luminous flux,

a measure of the total "amount" of visible light emitted by a source. The

more lumen a flash can emit, the bigger the flash intensity.


3

Colour temperature (Kelvin) is a property of the flash itself and cannot be

adjusted by any other means than simply buying a new flash.

Using these variables, the flash can be adjusted to best suit the photogra-

pher’s needs. (Axford, 2000) (Galitz, 2003-2007) (Stensvold, 2002)

3.2 Flash synchronization

A flash has no real use unless it is synchronized with the camera taking the

picture. The flash has to be fired the exact moment the shutter of the camera

lens is at its widest. This allows the lens to take as much light as possible

on the camera sensor when taking the picture. In modern cameras, this is

usually accomplished through the hot shoe of the camera, a mounting point

on top where you can connect your flash, and is in direct communication

with the camera that will tell it when to flash and how much light is neces-

sary at each given time. There are different standards of synchronization,

but the most recent ones are X-sync (Xenon flashes) and HSS (High Speed

Sync). These are all brand related types of synchronization. We will not go

into them for the reason that we will not need these synchronizations as we

will use the manual mode which is available on all brand of SLR cameras.

(Buff, n.d.)

3.3 Types of high-speed flash

There are multiple ways to make a high-speed flash. It all depends on the

type off light emitting source used. We make a difference between three

types.

LED (light emitting diode) bulbs

ARC bulbs, a lamp that produces light by an electric arc in an ionized

gas like Xenon.

Air-gap flash, a high-speed flash created by a spark between two elec-

trodes in an air filled glass tube starting at around 16.000Volts. (Tirosh,

2013) (glacialwanderer, 2011)

We quickly eliminate the Air-gap flash. Although it shows the best potential

as a high-speed flash it is dimensionally unsuited for our application and

too dangerous. It presents various high safety risks for the user.

3.4 LED versus ARC lamps

PRICE:

Power LEDs are becoming more popular and with the constant improving

of this technology, the prices of these power LEDs are constantly dropping,

ranging from 10EUR to 100EUR for a decent lumens value while ARC

flash lamps (such as Xenon bulbs) are rather expensive with a starting price

of 50EUR for a bulb and the need for a more complex electronic system

which results in an even higher price.

PULSE WIDTH AND SPEED:


4

Power LEDs have a rise time of only 5-10ns which allows for the creation

of a very short pulse width, while an ARC flash lamp has a minimum pulse

width duration of ±10µs. (Perkin Elmer, 2013)

As shown on Figure 1, the LED is much faster in the reaction to a pulse and

is easier to extinguish.

Figure 1: Time trace of light emission as detected by a photodiode (upper trace) for a high-

power LED (left) and a conventional xenon flash lamp (right) in response to a

trigger pulse (lower trace). (Willert, 2010)

VOLTAGES AND POWER:

While Power LED voltages are starting at 3V, the voltage for an ARC lamp

is much higher, running in the hundreds of volts. They have a considerable

higher power consumption. It is one of the reasons you will not find them

on phone cameras (with some exceptions). (Perkin Elmer, 2013)

LIGHT INTENSITY:

The big advantage of ARC flash lamps is the high intensity of the flash

starting somewhere around 200.000 lumens while Power LEDs are only ca-

pable of delivering a fraction of that intensity with around 200 lumens for a

3V power LED in constant use. By using multiple LEDs and put them in

overdrive for a very short amount of time (<10µs) the light intensity of a

standard ARC bulb can be approached. (CAP-XX, 2006)

3.5 Flash in our project

The flash designed in this thesis was a high-speed (up to 10 flashes per sec-

ond), high-intensity flash with a very short duration (100ns to 1µ). ARC

bulb technology was not used as this is too slow and expensive, so instead

a regular power LED was used. This should produce intensity needed, and

LED-technology certainly is fast enough to provide the light durations that

were required. The flash has to be adjustable in pulse width.

4 COMPONENTS


5

4.1 Block Diagram

Hot shoe cameraPC sync

Monostable multivibrator

Totem-pole construction

LED DRIVER

5V 5V 5V 24V

LED

Constant current

Figure 2: Block Diagram of the designed flash

The diagram (Figure 2) shows the different steps from the moment the cam-

era sends a signal until the actual flash given by a LED. Everything was

designed with the purpose of having as less of a delay time as possible.

The process starts when the shutter of the camera is at its widest and the

camera decides the flash is needed. The switch on the hot shoe will close

and a rising edge signal is created to trigger the monostable multivibrator.

The monostable multivibrator will create a low current pulse with a width

between ±90ns-2.1µs, depending on the chosen resistance timing value. The

low current pulse will activate the Totem-pole who acts as a fast rising cur-

rent amplifier and will enable the LED driver. Another function of the to-

tem-pole is to block the current to the LED driver at high speed as soon as

the created pulse starts falling. The Led driver is ensuring a constant high

current of 10.5A for the driving of the LEDS.

In the following pages each individual part will be looked at in more detail.

4.2 Hot shoe Camera (PC sync)

The flash had to be synchronized which means that a flash is fired on the

precise moment of the camera's peak shutter opening. This was accom-

plished by using the build-in signal given by the camera on the hot shoe.

The hot shoe (Figure 3) is a mounting point on the top of a camera to attach

a flash unit and is found on most single-lens reflex camera’s (SLR). For

Canon, the brand that is used for this study, it consist out of 4 smaller dot

contacts, 1 large dot contact in the middle and the bracket which is a com-

mon ground.

The large dot contact and the ground act like a switch that closes when the

camera fires the flash.

It uses the 4 smaller contacts to communicate with a speedlight unit. The

communication is a complex protocol which is a well-kept secret and differs

from one camera brand to another. It can only be used under licence, alt-

hough information can be found on projects were they tried to reverse en-

gineer the communication protocol. These communications are only in-

tended to see if the flash is ready to fire and to transmit the automatically

calculated power value to the speedlight.

A simpler solution and a work-around for the protocol is using the manual

flash mode of the camera. The manual mode is intended to allow the pho-

tographer to take complete control of how much power comes out of the


6

flash, therefore skipping the communication protocol. Typically, in the

manual mode, a speedflash is either connected to the camera by mounting

it on the Hot Shoe or by the use of a PC sync (Prontor–Compur) connection.

The PC sync cable is perfectly suited for the purposes of this study and is

therefore used.

The synchronisation process is simple; by putting a PC sync connection foot

(Figure 3) on the hot shoe of the camera, a PC sync cable is connected be-

tween the connection foot and the self-build flash system.

When the camera needs the flash it will simply shorten the two contacts and

thus act as a switch. A voltage of 5 Volts will be put on these contacts and

the resulting rising edge signal will go to the monostable multivibrator.

The hot shoe switch is connected to the B input of the monostable multivi-

brator and with the resistor R1 which makes sure that the B input is con-

nected to the ground if the switch is open.

Figure 3: Hot Shoe PC Sync connection foot (amazon.com)

4.3 Monostable multivibrator

Monostable multivibrators have only one stable state and produce a single

output pulse when it is triggered externally. These multivibrators only re-

turn back to their first original and stable state after a period of time deter-

mined by the time constant of the RC coupled circuit. (Storr, 2014) (Floyd,

2006)

At first, experiments were conducted with a 555 timer IC. This is the most

common and most sold timer IC ever made. By connecting the

DISCHARGE and the THRESHOLD pin of the 555 together and adding an

external resistance and capacitor, a monostable multivibrator is made

(Figure 4). Experiments with this 55 timer IC showed this component to be

incapable of producing a pulse small enough in width to meet the demands.

Although the minimum pulse width time is not stated in the datasheet of the

555, searches on the internet confirmed the suspicion that it is impossible to

accomplish the goals of this study with the 555 IC and thus started the

search for another monostable multivibrator.


7

Figure 4: The 555 IC as a monostable multivibrator. (Digital fundamentals, Floyd)

Using the Mouser database and filtering on availability, Datasheets from

promising components were checked. Eventually the SN74LVC1G123 IC

is chosen because of its ability to create pulses with a minimum width of

±90ns and it has a very short delay time of 8.7ns with a supply voltage of

5V. It also comes in a SSOP-8 package, which is solderable by hand.

The SN74LVC1G123 from Texas Instruments is a single retriggerable

monostable multivibrator designed for 1.65V to 5.5V VCC operation.

This monostable multivibrator features output pulse-duration control by

three methods, see Table 1. In the first method, the A input is low, and the

B input goes high. In the second method, the B input is high and the A input

goes low. In the third method the A input is low, the B input is high, and the

clear (CLR) input goes high. (Texas Instruments, 2004)

Figure 5: Internal schematic of the monostable multivibrator IC (Texas Instruments, 2004)

Table 1: Logic table of the monostable multivibrator (Texas Instruments, 2004)


8

Input B is used for the incoming signal from the PC sync cable. Input B will

act on the rising edge of the PC sync cable signal (see Table 1) and will go

through the built-in Schmitt-trigger as seen in Figure 5. The Schmitt-trigger

will activate the Monostable multivibrator and create the chosen pulse width

on the output Q.

4.3.1 Calculation of the pulse width

Figure 6: Monostable multivibrator INPUT/OUTPUT timing diagram (Texas Instruments,

2004)

The pulse width tw of the output Q is determined by the time constant of the

exterior resistance and the exterior capacitance (Figure 6) according to the

following formula (1):

𝑡𝑊 = 𝐾. 𝑅𝑒𝑥𝑡. 𝐶𝑒𝑥𝑡 (1)


9

With “K” being a changing factor depending on the used capacitor, the sup-

ply voltage and the temperature of the monostable multivibrator.

It is impossible to calculate the “K” value because there is not enough in-

formation provided by the manufacturer. Instead the graph (Figure 7) that

is provided by the manufacturer was used to determine the exterior resistor

and exterior capacitor.

Figure 7: Output Pulse Duration vs External Timing Capacitance graph (Texas Instru-

ments, 2004)

Using the graph (Figure 7), the conclusion was made that by using a capac-

itor of 10pF and a resistance between 1kΩ and 50kΩ, the pulse width can

be controlled between 90ns and 2µs.

Because the system doesn’t allow resistances of under 1kΩ a basic re-

sistance of 1kΩ in series with a potentiometer of 50kΩ (Figure 8) was used,

creating a theoretically controllable pulse width between ±90ns and ±2.1µs.

1kΩ 10pF50kΩ 5V

Rext/Cext Cext

Figure 8: Construction of the RC timing network

The resulting circuit build around the 74LVC1G123 can been seen in Figure

9.


10

Figure 9: Overview of the monostable multivibrator network

4.3.2 Measurements on the monostable multivibrator

To simulate a signal from the camera, a function generator was connected

to the connector where the hot shoe would be connected. The positive plug

goes into the slot connecting this plug to the B-entrance of the IC and the

negative plug is connected to the ground. The signal connected was a block

wave of 5V peek-to-peek voltage, with a DC-offset of 2.5V. This makes the

signal a switch that simulates the trigger signal from the hot shoe by con-

stantly switching between 0V (switch open, no flash) and 5V (switch

closed, flash on).

Measuring on the monostable multivibrator, as seen on Figure 10, where

channel 1 (upper trace) is the input signal and channel 2 (lower trace) the

output signal, a couple of observations could be made.

Turn-on delay time: The real turn-on delay time could not be accurately

measured because it depends on the rise time of the input signal used,

we can conclude however that the monostable multivibrator already

starts rising with an input voltage of 2.5V

Rise-time: It took 80ns to rise from 0V to 5V but already after 20ns the

output of the monostable multivibrator reached 4V which was a high

enough voltage to trigger the totem pole construction.


11

Figure 10: Rise-time and delay-time between input signal and output signal of the

74LVC1G123 monostable multivibrator.

The minimum pulse width generated by the 74LVC1G123 can be seen in

Figure 11. The calculation of the RC value suggested we could not go under

±90ns. The total pulse duration is indeed 90ns but instead of generating a

clear square wave, a spike was produced that was only 4V high and already

started dropping after 30ns as seen in Figure 11.

Figure 11: Minimum pulse width generated by the 74LVC1G123 monostable multivibrator.

The maximum pulse width generated by the 74LVC1G123 can be seen in

Figure 12. The calculations made showed a maximum pulse width of

±2.1µs, but the practical maximum pulse was 1µs instead. This was only

half of the calculated value. It was no problem for the end result of this study

but it certainly is peculiar.

The pulses generated by the monostable multivibrator above 200ns were

almost perfectly square except for a small constant overshoot when rising

and an undershoot when falling as demonstrated in Figure 12 and Figure 13.


12

Figure 12: Maximum pulse width (1µs) generated by the 74LVC1G123 monostable multi-

vibrator.

Figure 13: Pulse width of 500ns generated by the 74LVC1G123 monostable multivibrator.

4.4 Totem-pole

One of the most popular and cost effective drive circuits for driving

MOSFETs is a bipolar, non-inverting totem-pole driver. The idea behind it

is that, by using the very fast operation and high gain of bipolar transistors,

the gate can be quickly charged and discharged.

This circuit handles the current spikes and power losses making the operat-

ing conditions for the pulse width controller more favourable. Of course,

they should be placed as close as possible to the high power MOSFET they

are driving. That way the high current transients of driving the gate are lo-

calized in a very small loop area, reducing the value of parasitic induct-

ances. (Balogh, 2006)

4.4.1 Construction of the totem-pole


13

In the schematic, the totem pole transistors are NPN transistor Q2 and PNP

transistor Q3 as seen in Figure 14. The construction works in three stages.

(Damad, 2012)

Figure 14: Overview of the totem-pole

First stage (Figure 15)

When the power is turned on, C2 will quickly charge up through R6 and

hold a charge. R6 makes sure that the current is limited at 1.5A. At first

there will be no signal coming from the pulse generator responsible for

the triggering of the flash. The input signal is low. This means that tran-

sistor Q2 is off and transistor Q3 is on. The gate of the MOSFET is con-

nected to the ground and closes off any current going from the

MOSFET source to drain, no current can flow in the power circuit.


14

Figure 15: powering up the totem-pole circuit and pulling MOSFET gate to the ground

Second stage (Figure 16)

A pulse from the monostable multivibrator at 50mA through the resistor R4

is send to the bases of Q2 and Q3. This will activate Q2 and it will pass a

collector-emitter current. Q3 will go into cut-off mode and no longer con-

nect the MOSFET gate to the ground. This means that the high current from

the 5V power supply, and on top of that the discharge current from capacitor

C2 can now push their current into the gate of the MOSFET. This forces the

MOSFET to instantly open and send a current through the drive circuit,

making the LED light up.


15

Figure 16: Positive pulse, MOSFET is forced to open

Third stage (Figure 17)

When the pulse ends, meaning that the LED should extinguish, Q2 will go

into cut-off mode while Q3 will pass and quickly connect the gate of the

MOSFET to the ground. This allows the build-up charge in the gate input

capacitance of the MOSFET to discharge to the ground, resulting in a quick

shutdown of the MOSFET. This brings us back to stage one.

Figure 17: totem-pole Pulse has ended


16

4.4.2 Measurements on the totem-pole

On the scope image on Figure 18 can be seen how the totem-pole reacts on

a pulse given by the monostable multivibrator. Were the original pulse orig-

inated from the Q output of the monostable multivibrator was an almost

clean square wave, the new pulse that is given to the gate of the MOSFET

has some small wrinkle in the beginning and takes longer to rise and fall.

As seen on Figure 19, there is a small delay of 20ns before the totem-pole

reacts and start to rise. The rise time is still the same but is less steep than it

was on the output of the monostable multivibrator.

Figure 18: Signal on the MOSFET base on channel 1 (upper trace) and output monostable

multivibrator on channel 2 (lower trace).

Figure 19: Signal on the MOSFET base on channel 1 and output monostable multivibrator

on channel 2 with channel overlap.

Figure 20 shows how much delay there is between the moment a rising edge

is presented on the input of the monostable multivibrator and the pulse pre-

sented at the base of the MOSFET. There is a delay of 110ns between the

moment the input of the monostable multivibrator reached 5V and the

MOSFET gate reaches 5V. Although this seems a long time, the real delay

is smaller because of the fact that current is also rising and will reach the

break current of the MOSFET before the 5V is reached.


17

Figure 20: Rising edge on input B of the monostable multivibrator on channel 1 (upper

trace) and signal on the MOSFET base on channel 2 (lower trace).

4.5 LED DRIVER

4.5.1 Construction of the LED driver

LEDs are most efficient and reliable when driven by a constant current. This

is to make sure the same brightness level is reached every time they are put

to use and so the current going through the LED is not too high which would

result in a destroyed LED.

In the following circuit, a MOSFET is used in combination with a standard

NPN BJT. Through the resistor R5, a driving current is coming from the

totem-pole to the FET gate. When this happens, the FET drain and source

are effectively shorted allowing current to flow through the LED and R7.

This is where the BJT transistor Q4 comes into play. The base of the tran-

sistor won't want to go higher than some set voltage: Vbe. This value can

vary among transistors, but in this instance it typically is 0.7V for a standard

2N3904 NPN BJT. At this voltage, Q4 will also turn on and allow current

to flow through Q4, diverting voltage from the gate of Q1. With less voltage

at the gate of Q1, it begins to turn off" These two transistors will battle back

and forth to be in the on state, effectively creating a constant current source

through the LED. (Clothier, 2012)


18

Figure 21: LED driver circuit

As a MOSFET, the IRF540was chosen, which is a MOSFET with following

important specifications for our purpose. (Vishay Siliconix, 2011)

Rise time = 44ns

Turn-On Delay time = 11ns

Turn-Off Delay time = 53ns

Fall Time = 43ns

Pulsed Drain Current = 110A

Drain-Source Voltage = 100V

Gate-Source Voltage = 20V

The NPN transistor 2N3904 has following important specifications.

(Central Semiconductor, 2012)

ton = 70ns

toff = 250ns

Vbe Typical = 0.7V

The system was calculated to give a constant current of 10.5A through the

LED, this was done by calculating the value of R7 with the following for-

mula (2). (Lazaridis, 2012)

𝑅7 =

𝑉𝑏𝑒

𝐼𝑓_𝐿𝐸𝐷 (2)

It is known that Vbe= 0.7V and the desired current is If_LED= 10.5A


19

𝑅7 =0.7𝑉

10.5 𝐴= 0.067Ω ≈ 0.062Ω

With such a small resistance and such high currents, R7 has a power resistor.

The next step is determining the power dissipation of the MOSFET, this is

calculated in the following matter. (3)(4) (Lazaridis, 2012)

𝑉𝑚𝑜𝑠𝑓𝑒𝑡 = 𝑉𝐷𝐷 − 𝑉𝑅7 − 𝑉𝑓_𝐿𝐸𝐷 (3)

𝑃𝑚𝑜𝑠𝑓𝑒𝑡 = 𝑉𝑚𝑜𝑠𝑓𝑒𝑡 ∗ 𝐼𝑓_𝐿𝐸𝐷 (4)

𝑉𝑚𝑜𝑠𝑓𝑒𝑡 = 24𝑉 − 0.7𝑉 − 16.64𝑉 = 6.66𝑉

𝑃𝑚𝑜𝑠𝑓𝑒𝑡 = 6.66𝑉 ∗ 10.5𝐴 = 69.63𝑊

The conclusion here is that a lot of power is lost over the MOSFET, which

does not make this a very efficient system to use but it is needed for the

constant current. One of the solutions would be to add an extra LED that

works on a lower voltage in series with the original LED. This would result

in extra light for the flash system and a lower power dissipation over the

MOSFET.

If the LZ1-10CW02-0065 would be added, which works on a peak voltage

of 4.2V, the new formulas would be: (5)(6)

𝑉𝑚𝑜𝑠𝑓𝑒𝑡 = 𝑉𝐷𝐷 − 𝑉𝑅7 − 𝑉𝑓_𝐿𝐸𝐷1 − 𝑉𝑓_𝐿𝐸𝐷2 (5)

𝑉𝑚𝑜𝑠𝑓𝑒𝑡 = 24𝑉 − 0.7𝑉 − 16.64𝑉 − 4.2𝑉 = 2.46𝑉

𝑃𝑚𝑜𝑠𝑓𝑒𝑡 = 𝑉𝑚𝑜𝑠𝑓𝑒𝑡 ∗ 𝐼𝑓_𝐿𝐸𝐷 (6)

𝑃𝑚𝑜𝑠𝑓𝑒𝑡 = 2.46𝑉 ∗ 10.5𝐴 = 25.83𝑊

This is an immense improvement which results in a more efficient system.

4.5.2 Measurements on the LED driver

After testing, a few alternations had to be made to the original schematic:

Only a power supply of 12V was at our disposal, so 12V was used in

the power circuit.

Because of the 12V, only the LZ1-10CW02-0065 LED could be used.

The measurements were made with 2 of such LEDs.

Because of the very small pulse times, the need for Q4 disappeared in

practical use. The voltage drop over R7 was enough to ensure a constant

current.

Resistance R7 was switched out for smaller value of 0.05Ω to create a

higher current

A diode was placed over the LEDs to protect them from negative cur-

rents.


20

While testing one of the LEDs broke because of shortening on the contacts.

This seemed like a bad thing but it actually helped a lot. It made clear that

even while in normal use the LEDs only ask 4.2V over anode and cathode,

it almost doubled when put in overdrive. This meant that a single LED

needed 7.4V over it as can be seen in Figure 22.

Figure 22 and Figure 23 clearly show how fast the MOSFET reacts to a

pulse given on his gate, it almost instantly turns on within 40ns.

The maximum pulse that can be delivered by the LED is 1µs long, the small-

est that can be delivered is as small as 100ns. If the system is pushed farther

and tries to even go smaller, the LED will not have the time to drain enough

current and will therefore never deliver enough light, as can be seen in Fig-

ure 24.

Figure 22: Maximum pulse possible: channel 1 is the voltage measured at MOSFET drain,

channel 2 is the voltage measured at MOSFET gate.

Figure 23: Minimum pulse possible: channel 1 is the voltage measured at MOSFET drain,

channel 2 is the voltage measured at MOSFET gate.


21

Figure 24: Pulse to short, LED barely lights up: channel 1 is the voltage measured at

MOSFET drain, channel 2 is the voltage measured at MOSFET gate.

By measuring the voltage over resistor R7, the current trough the LED can

be calculated. Resistor R7 has a value of 0.05Ω and the voltage over it is

between 700mV and 500mV (Figure 25). Within the time of the pulse a

current between 14A and 10A will go through the LED.

When the pulse is finished, there seems to be bad oscillating voltage spikes.

By adding a snubber capacitor of 220nF over the drain and source of the

MOSFET, as seen in Figure 26, it looks like a lot of the oscillation disap-

peared but making the pulse longer and les steep. Looking back at Figure

22 without the snubber, it seems there is no oscillation. Conclusion being

that it doesn’t affect our LED and the snubber should not be placed.

Figure 25: Channel 1 is the voltage measured over R7, channel 2 is the voltage measured at

MOSFET gate.


22

Figure 26: Channel 1 is the voltage measured over R7 with added snubber of 220nF, channel

2 is the voltage measured at MOSFET gate.

4.6 LED

4.6.1 LED in overdrive

A study conducted by Chris Willert and his team at the German Aerospace

Center (2010) was examining the possibility of using high-powered light

emitting diodes (LEDs) as light sources in flow diagnostics, in particular,

as an alternative to laser-based illumination in particle imaging.

They discovered that LEDs can be operated significantly beyond their dam-

age threshold using high-current, short duration pulses. In this case, the tem-

perature within the substrate (junction temperature) stays below the damage

threshold while the photon generation per time unit is approximately in-

creased in proportion to the current increase. This makes the LED particu-

larly interesting for utilization as a pulsed light source in image based diag-

nostics. (Willert, 2010)

The study shows that they have been able to overdrive LEDs to over 20

times their normal rated current without destroying them for a pulse width

under the 20µs. This while their light intensity almost linearly increased.


23

Figure 27: Luminosity of high-power LEDs driven with 1 kHz current pulses of τ p = 1μs

duration.

The decision was made to increase the current flowing through the LEDs

by a multiplier of 15. This is to make sure the LEDs would not be burned

and to leave room for improvement if needed.

4.6.2 Chosen LEDs

The following LEDs have been chosen because of a couple of reasons:

They both have a colour temperature of 6500 Kelvin, which is ideal for

electronic flashes.

Their forward voltages; because they both are in series we will have to

add their voltages together which results in a total voltage of 20.84V.

This is ideal with a supply of 24V.

Their high basic luminous flux which will only grow when we put the

LEDs in overdrive.

The ability to solder the LEDs without the help of machines. Most

power LEDs that are sold have a very difficult SMD package but these

ones can be bought on a MCPCB package. (Figure 28)


24

Figure 28: LZ4-40CW08-0065 on a MCPCB (MOUSER.com)

4.6.3 LZ4-40CW08-0065

This is the main power LED being used. It has following specifications:

(LED Engin, 2013)

Table 2: LZ4-40CW08-0065 specifications

Brand LED Engin

Temperature 6500 Kelvin

If_normal 700mA

Luminous Flux (with If_normal) 680lm

Maximum forward voltage 16.64V

Model LZ4 emitter on Standard Star 1

channel MCPCB

Like stated before, this LED will be used in overdrive. By increasing the

forward current (7), the luminous flux will be increased as well.

𝐼𝑓_𝐿𝐸𝐷 = 𝐼𝑓_𝑛𝑜𝑟𝑚𝑎𝑙 ∗ 𝑎𝑚𝑝𝑙𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 (7)

𝐼𝑓_𝐿𝐸𝐷 = 0.7𝐴 ∗ 15 = 10.5𝐴

This would result in a luminous flux of approximately: (8)

𝛷𝑣_𝑜𝑣𝑒𝑟𝑑𝑟𝑖𝑣𝑒 ≈ 𝛷𝑣_𝑛𝑜𝑟𝑚𝑎𝑙 ∗ 𝑎𝑚𝑝𝑙𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 (8)

𝛷𝑣_𝑜𝑣𝑒𝑟𝑑𝑟𝑖𝑣𝑒 ≈ 680𝑙𝑚 ∗ 15 ≈ 10200𝑙𝑚

4.6.4 LZ1-10CW02-0065

This is the second and weaker LED that could be used to have a more effi-

cient system. It could be used to have more light on the edges of the image.


25

It has following specifications: (LED Engin, 2015)

Table 3: LZ1-10CW02-0065 specifications

Brand LED Engin

Temperature 6500 Kelvin

If_normal 1000mA

Luminous Flux (with If_normal) 228lm

Maximum forward voltage 4.2V

Model LZ1 emitter on Standard Star

MCPCB

Same as before the new luminous flux is calculated when putting this LED

in overdrive with a constant current of 10.5A. First off the amplification

was sought using formula (7). With the amplification we can find the new

flux using formula (8).

𝑎𝑚𝑝𝑙𝑖𝑓𝑖𝑐𝑎𝑡𝑖𝑜𝑛 =10.5𝐴

1𝐴= 10.5

𝛷𝑣_𝑜𝑣𝑒𝑟𝑑𝑟𝑖𝑣𝑒 ≈ 228𝑙𝑚 ∗ 10.5 ≈ 2394𝑙𝑚

4.7 Complete schematic of the high speed flash

Bringing everything discussed above together in one schematic it would

look like Figure 29 with the component list found in Table 4.

Table 4: circuit component list

R1 1kΩ

R2 1kΩ

R3 50kΩ potentiometer

R4 22Ω

R5 4,7Ω

R6 3,3Ω

R7 0.062Ω 10W power resistor

C1 10pF

C2 1000µF

Q1 IRF540

Q2 BC639

Q3 BC640

Q4 2N3904

S1 Hot Shoe Adapter with PC Sync Port

U1 Texas Instruments 74LVC1G123 monostable mul-

tivibrator

LED1 LZ4-40CW08-0065

LED2 LZ1-10CW02-0065

V1 Computer PSU 600W

V2 Computer PSU 600W


26

Figure 29: complete schematic of the designed circuit


27

5 PRINTED CIRCUIT BOARD

To practically implement our device, a Printed Circuit Board (PCB) was

developed. The schematic used for the creation of this PCB was slightly

adapted to fit connections where necessary.

Figure 30: PCB design schematic

As seen in Figure 30, some components have been swapped out with con-

nectors. The components concerned were both power supplies, the hot shoe

connector acting as switch and the power LEDs. These connectors provide

our system with the capability to interchange components. These capabili-

ties include:

5V power supply connector (J1): any 5V power supply can be con-

nected here that is capable of delivering the 1.51 amps needed to drive

the MOSFET and the 100 mA needed to supply the monostable multi-

vibrator. The power supply should be as stable as possible because the

accuracy of the monostable multivibrator pulse width depends on it.

Hot shoe connector (J3): this connector enables the use of any 5V rising

edge signal as a trigger for the monostable multivibrator.

LEDs connector (j4): using a connector for this part of the schematic,

the LEDs used can be varied. These LEDs will be mounted on a sepa-

rate PCB, so any variation of LEDs with different power output and

voltages are possible, both in series and parallel. However, the power

supply for the high power part of the schematic, 24V in this case, and

the current-limiting resistor R7 have to be adapted accordingly.

24V power supply: When using other LEDs, this power supply has to

be adapted accordingly. This connector enables the usage of power sup-

plies of varying voltages and power outputs, in order to correctly drive

the LEDs.


28

Figure 31: Component layout of the designed PCB

On Figure 31 the PCB layout is shown. The aim of the PCB was to make it

as compact as possible. All components are through-hole, except for the

monostable multivibrator, which is SMD. As a result, this component was

placed on the bottom of the PCB where the copper conductive traces are.

The connectors have been placed on the sides of the PCB as these have to

be easily reachable.

One of the most important parts of the print was the totem pole part. The

totem pole configuration required all 6 components involved to be close

together. These components are:

The monostable multivibrator IC1

Resistor R4, connecting the bases of the totem pole transistors to the

monostable multivibrator

Both totem pole transistors, Q2 and Q3

Resistor R5, connecting the high supply current from the totem pole to

the gate of the LED driving MOSFET

MOSFET Q1, acting as LED driver


29

Figure 32: Component layout of totem pole configuration

On Figure 33, this totem pole configuration is identified by a red polygon

circling the components involved. All components were placed in close

proximity to each other. As a bonus, the resistor R7, controlling the current

in the high power circuit, and the transistor Q4, controlling the MOSFET

gate current, were also placed close to the totem pole configuration.

Figure 33: Trace layout of the PCB

Finally, after the components were placed on the board, the routing was

done, as seen in Figure 33. Different trace thicknesses had to be used as a


30

result of different currents flowing through the multiple parts of the sche-

matic.

In terms of current flowing through the connecting traces, 3 parts were dis-

tinguished and are highlighted on Figure 34.

A low-power circuit, mainly around the monostable multivibrator, with

a conventional current of a few hundred mill amperes, supplied by the

5V power supply

The part of the totem pole construction that allows a current of around

1.50A to flow through the totem pole to the MOSFET driver, also

supplied by the 5V power supply, marked in yellow on Figure 34

The high power circuit with the MOSFET and the LEDs, powered by

the 24V power supply, marked in red on Figure 34

Figure 34: PCB divided in parts in terms of current

Using a reliable online trace width calculator (Suppanz, 2007), the trace

width of the copper was calculated for these three parts separately. Inputs

that matter for this particular study are current (in Amperes), copper layer

thickness of the print (35µm), ambient temperature (default 25°C) and tem-

perature rise (default 10°C).

For the calculation of the totem pole construction and all components

included in this part, the maximum possible current was doubled and

temperature rise was left on default. The result was a trace width of

1.37mm. This can be seen in the part marked in yellow on figure 5.

The high current part around the MOSFET and LED has to bear a large

current of 16A. This is why a higher temperature rise was allowed. It

has been set to 75°C. The other values remained default. The calculator

gives us a trace width of 4.05mm, but for practical reasons a trace width

of 2mm has been chosen. The reasoning behind this is that the high


31

current pulse is so short in duration that the trace will not have the time

to heat these 100°C total. On top of this, tin solder will be added on top

of the trace to increase heat dissipation. If this proves inadequate, or

thinner traces are required, thick copper wire of approximately 1mm2

can be soldered on top of the traces to allow higher currents. These

traces can be seen on figure 5 marked in red.

The remaining traces are low current traces, used for sending signals

and supply current/voltage to and from the monostable multivibrator

IC. For these traces all values will be left on default, except for the cur-

rent. Conventional current in these traces will be a few hundred

milliamps. Therefor the traces were calculated for use with 1 Ampere

currents. The calculator gives us a result of 0.088 mm thickness. From

a practical point of view this was too thin for the etching process used.

Therefor the width was increased to a more suitable 0.4mm. Traces us-

ing these width are all the remaining traces not marked by the previous

totem pole and high power circuit parts.

6 DSLR CAMERA

As a camera, a DSLR was used. A digital SLR is a digital camera combining

the optics and the mechanisms of a single-lens reflex camera with a digital

imaging sensor. This could be a camera of any of the big brands who use

the ISO 518:2006 standard size hot shoe (Nikon, Canon, ...) and has a man-

ual flash mode.

Some of the many advantages of a DSLR are:

Digital SLRs have large image sensors that produce high-quality photos

The lenses of DSLR cameras are interchangeable

An SLR has a very small lag time, and is ideal for action photography

The different stages of taking a digital picture can be seen in Figure 35 and

are: (Roberts, 2013)

1. Light passes through the lens and strikes a mirror (green)

2. The mirror reflects the light up to a focusing screen

3. Light passes through the focusing screen and enters a block of glass

called a pentaprism (orange)

4. The pentaprism reflects the image so that it can be seen in the view-

finder or on the screen.

5. When the photo is taken, the mirror flips up and a shutter (blue) opens

that exposes the digital sensor (red) to light


32

Figure 35: layout of a SLR (Roberts, 2013)

It is in this last stage when the shutter is at its widest that the flash will be

flared.

7 POWER SUPPLY

A power supply is an electronic device that supplies electrical energy to an

electrical load. The primary function of a power supply is to convert one

form of electrical energy to another, so basically it is an electric power con-

verter. Power supplies are used for various appliances, with various power

input and output forms. The device we will use is a Power Supply Unit from

a desktop computer as this has a lot of characteristics that we need.

(Malmstadt, 1981)

7.1 Computer Power Supply Unit

A Power Supply Unit (hereafter mentioned as PSU) is a power supply for

desktop computer, providing the power needed to the motherboard and the

peripheral devices. The reason the PSU from a desktop computer is used, is

because it gives a very steady output current and voltage. A computer moth-

erboard has to be provided with a very accurate and stable voltage and cur-

rent. The dropping of current or voltage has to be avoided at all costs. These

specifications are helpful in providing a high and steady current to the LEDs

being used. The PSU also has the desirable voltage outputs of +5V, -12V

and +12V which will be used to respectively power the IC’s used and the

LEDs used. Figure 36 shows the schematic of a typical PSU.


33

Figure 36: Principal circuit diagram of a PC power supply (Hans Haase)

As can be seen in this schematic, there are different output voltages. The

+3.3V output was not used, but the +12V, -12V and +5V outputs were used

because of the reasoning mentioned above. A voltage of 24V can be ob-

tained when using the +12V output in combination with the -12V output.

(Chin, 2007) (Torres, 2008)

7.2 Power Factor (PF) and Power Factor Correction (PFC)

The power factor (9) defined as the ratio of real power (P) to the apparent

power (S) in the circuit and is a dimensionless number between -1 and 1.

This is an important factor to take into account when selecting a power sup-

ply.

𝑃𝐹 =𝑃

𝑆 (9)

AC power has 3 components:

Real power or active power (P) in Watts (W)

Apparent power (S) in Volt-Amperes (VA)

Reactive power (Q) in reactive volt-amperes (VAR)

The Volt-Amperes and Reactive Volt-Amperes are non-SI units identical to

Watts, used in engineering practice to easily differentiate the three power

components. In the theoretical case the real power component equals to the

apparent power, but in practice the voltage and current aren’t in perfect

sync; one lags behind on the other, resulting in a loss of power. This means

the power supply will not be able to deliver maximum power as if it were a

theoretical power supply. There are different ways to minimize this lag (thus

increasing the power factor as the real power approaches the apparent

power.

Power Supply Units may have Power Factor Correction (PFC). There are

three different ways of PFC:


34

Passive PFC: A filter (consisting of capacitors and inductors) is used

that only passes current at the line frequency (50-60Hz). This requires

larger capacitors and inductors that active PFC.

Active PFC: changing the waveform of the current drawn by the load

with the use of power electronics. A big advantage is that SPU’s with

active PFC can operative on a wide variety of input voltages (100V-

230V) of different countries.

Dynamic PFC: Quickly connect/disconnect capacitors or inductors us-

ing semiconductor switches (typically thyristors).

In this project, a PSU with active PFC is preferred, as this gives the highest

power factor (up to 99%). This is desired because the device that was made

had to be accurate enough to provide the correct power to the LEDs. (W.

Mack Grady, 1993) (Rozenblat, 2014-2015)

7.3 Power supply calculation

The calculation for the needed power supply is fairly simple. The current

needed for the LEDs was 10.5A. With the possibility to upgrade later, by

putting two extra LEDs in parallel over the two existing LEDs, the total

current would double to 21A.

The power needed for the driving of the LEDs is negligible compared to the

power consumption of the LEDs. (10)

𝑃 = 𝑉𝑑𝑑 ∗ 𝐼𝑓_𝐿𝐸𝐷 (10)

𝑃 = 24𝑉 ∗ 21𝐴 = 504𝑊

For safety reasons it is best to take a power supply with a 20% tolerance.

This would result in a new wattage of: (11)

𝑃𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 = 𝑃 ∗ 1.2 (11)

𝑃𝑡𝑜𝑙𝑒𝑟𝑎𝑛𝑐𝑒 = 504𝑊 ∗ 1.2 = 604,8 ≈ 600𝑊

It would be best to take a power supply of 600W, this seems much but it is

only used at very short bursts. The total power consumed will not be so high

because it is not used continuously.

8 CONCLUSION

From this thesis we can conclude that theoretically it is perfectly possible

to make a relatively cheap and working device meeting all the requirements

set in the assignment part. The design of the schematic was put together by

using pulse width modulation designs in combination with our own think-

ing. The hardest part of this project was actually finding the right compo-

nents that are both accurate and fast enough to maintain the flash system.


35

The biggest part of this thesis consisted of research for component and look-

ing everywhere to find faster, better, more accurate, cheaper components

than the ones we had found. The better we chose the components, the more

efficient the system would be, and the closer we could make it to fit the

requirements set by our supervisor. Another very important and time con-

suming matter was the driving of the LEDs. A lot of research was done to

find both the best and most efficient way to drive these LEDs with the power

provided.

But as it regularly is, the theory is not always what it is in reality. The result

is better than expected but there is still some research to do and some com-

ponents to add and delete that are not in the original system. So there is the

diode that should be put parallel over the LEDs to protect them from nega-

tive voltage spikes. Some big capacitors could also be add in the power cir-

cuit as to deliver a more stable voltage and current.

The conclusion of the power supply is that using the PSU was a mistake,

thinking that the -12V could be used to make a higher voltage of 24V. The

-12V is only intended to be a control voltage, no real current could be drawn

from it. Using two PSU’s of similar power could prevent this problem but

it is our opinion that using a good transformer with an even higher voltage

and with the ability to draw a big current would be a better solution.

It is a pity that we never had the chance to actual test our system with a

camera because of the missing PC sync cable that is at the moment of this

writing still in transit to be delivered. We have confidence that the system

should work how we said it would theoretically work.

Overall we are very content with the end result delivered and are sure this

system is ready to use with some small modifications. Little research and

testing is still needed.


36

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Appendix 1

DATASHEETS

high speed camera flash

Documents