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Part , Description , Radio Shack , Digi Key , Newark Notes

IC1 LM741 Op-Amp 276-007 LM741CN-ND LM741CN NE741,µA741, etc.

Q1 2N2222A transistor 276-2009 2N2222A-ND 2N3904 See text

D1 1N4148 Diode 276-1122 1N4148GICT-ND 1N4001 1N4001, or others

Th1 50K Thermistor KC005T-ND 96F3309 KC005T in prototype

Re1 12V Relay 275-249 Z753-ND 83F8057 RS is 1A

R1 15K, 5% resistor 84N2487 brown-green-orangeR2,R5 10K, 5% resistor 84N2479 brown-black-orange

R3 150K, 5% resistor 84N2485 brown-green-yellow

R4 4K7, 5% resistor 271-1330 50N1628 yellow-purple-red

R6 1K, 5% resistor 271-1321 50N6012 brown-black-red

R7 1K8, 5% resistor brown-gray-red

P1 100K Trimmer Pot Bourns

C1 10uF/25V Capacitor Electrolytic

C2 0.01uF, Capacitor Ceramic

Led Red, 3mm Light Emitting Diode Spare parts: 

Auto Fan Part on Board Q1 = 2N3053, 2N3904, NTE123A, ECG123A, NTE128, ECG128, etc.

D1 = 1N4001, NTE519, ECG519, NTE116 etc.

Th1 = Thermistor, 22K – 100K. 50K used in the prototype.

Re1 = Relay, Type 842-1C-C ―Fashion Electronics. Order # 50-333-0 (1.55 $)

Reed relay works well.

To give a better performance, the negative temperature coefficient thermistor (NTC) asthe temperature sensor should be placed as close as possible to the IC power transistor to make surea tight thermal contact, installing it on the heat sink is also a good idea. You also can set the VR1 attheheat sink temperature (70 degree Celcius). Another alternative (use at your own risk) is turn onyour amplifier volume to maximum and use your finger to touch the heat sink regularly and adjustVR1 to activate the fan at heat intensity until the maximum temp you can stand to touch. And theLEDindicator will give you the information that the fan is active.

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Read more: http://electronicsuite.com/regulate/automatic-fan-regulator-circuit-diagram-using-ic-lm311/#ixzz1Urm5dXQB 

Replacement Parts: Q1 = 2N3053, 2N3904, NTE123A, ECG123A, NTE128, ECG128, etc.

D1 = 1N4001, NTE519, ECG519, NTE116 etc.

Th1 = Thermistor, 22K - 100K. Used 50K in prototype.

Re1 = Relay. A reed relay will work too.

Newark Electronics 

Digi-Key 

Radio Shack/Tandy 

Radio Shack's pittyful selection of parts these days is a real headache.

So I'm no longer gonna waste my time looking for partnumbers. Unless I'm 

sure

they carry the part. Too bad... 

Couple Notes: Th1, the 50K thermistor, is a standard type. Mine was a bar or rectangular lookingthingy. Available from Tandy/Radio-Shack. Almost any type will do. I experimentedwith different models from 22K to 100K and all worked fine after replacing thetrimmer pot.The one used in the above circuit diagram was a 50K model made by Fenwal (#197-503LAG-A01). This 50K was measured at exactly 25 °C and with 10% tolerance. Theresistance increases as the surrounding temperature decreases. Tolerance for myapplication (cooling a large powersupply coolrib) is 10%. Another name for this thingis 'NTC'. NTC stands for "Negative Temperature Coefficient" which means when thesurrounding temperature decreases the resistance of this thermistor will increase. Youmay have to shop around to get the cheapest price. Some thermistors can be had for as

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little as $4.00 but as much as $55.00 Canadian currency for the glass encapsulatedtype (the best).I replaced my thermistor for a 60K hermetically sealed glass type since theenvironment for my application may contain corrosive particles which may affectperformance on a future date.

P1 is a regular Bourns trimmer potentiometer and adjusts a wide range of temperatures for this circuit. I used the 10-turn type for a bit finer adjustment but theregular type may work for your application.

R1 is a 'security' resistor just in case the trimmer pot P1 is adjusted all the way to '0'ohms. At which time the thermistor would get the full 12 volt and it will get so hotthat it puts blisters on your fingers... :-)R3 feeds a bit of hysteresis back into the op-amp to eliminate relay 'chatter' when thetemperature of the thermistor reaches its threshold point. Depending on yourapplication and the type you use for Q1 and Re1, start with 330K or so and adjust itsvalue downwards until your satisfied. The value of 150K shown in the diagramworked for me. Decreasing the value of R2 means more hysteresis, just don't use morethen necessary. Or temporarily use a trimmer pot and read off the value. 120K workedfor me.

Transistor Q1 can be a 2N2222(A), 2N3904, NTE123A, ECG123A, etc. Not criticalat all. It acts only as a switch for the relay so almost any type will work, as long as itcan provide the current needed to activate the relay's coil.

D1, the 1N4148, acts as a spark arrestor when the contacts of the relay open andeliminates false triggering. For my application the 1N4148 was good enough since thetiny relay I used was only 1 amp. However, you can use a large variety of diodes here,my next choice would be a regular purpose 1N4001 or something and should be usedif your relay type can handle more then 1 amp.

If you like to make your own pcb, try the one below. The pcb is fitted with holes forthe relay but may not fit your particular relay. It was designed for a Aromat HB1-DC12V type. The variety and model of relays is just to great. How to mount it then?

Well, I left ample space on the pcb to mount your relay. You can even mount it up-side-down and connect the wires individually. Use Silicon glue, cyanoacrylate ester(crazy glue), or double-sided tape to hold the relay in place. Works well. Note that thepcb and layout is not according to the circuit diagram in regards to the hookup of thefans. The PCB measures approximately 1.5 x 3 inches (4.8 x 7.6mm)If you print the pcb to an inkjet printer it is probably not to scale. Try to fit a 8-pin icsocket on the printed copy to make sure it fits before making the pcb...

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Automatic fan controller circuit

This circuit will turn on/off 12V DC fan or CPU fan when temperature above normal temperature.You can set turn ontemperature by adjust VR1. This circuit use an NTC (Negative temperature coefficient)which is a thermistor is one inwhich the zero-power resistance decreases with an increase in temperature. So If temperature increate the voltage atpin 3 on LM311 will decreated .The resistance of NTC is about 10K at 25′c. 

VR1 should be multi-turn potentiometer type such 10K/25 turn

 Abstract: 

The automatic temperature control system is a very essential feature of a factory 

or an industry. In most of the case the temperature plays a vital role in the

process of manufacturing or the process carried in that factory or industry. 

The most common and simplest way of controlling temperature is by using a fan

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 which is automatically connected to a network such as it is switched on when the

temperature of the surroundings increases. 

The change in temperature of the surroundings can be sensed with the help of 

thermistor or a sensistor. These electronic components sense the temperature of the surroundings. When there is a change in the temperatue tempetature then

these electronic components start to conduct the electric current. This is the main

principle of the automatic control devices. These devices can be extended to an

extent that we can set the temperature when the fan should rotate. 

Overview 

The circuits below are variations on basic thermostat designs that can

be used to control either heating or cooling devices. I've tried to make

them as simple, cheap, and thrifty with power as possible. I'm rather fond

of them. Potential applications include such diverse jobs as opening flaps

or controlling heat in greenhouses, powering automatic fans that only cut

in when needed, homebrew cooling and warming, air conditioning, space

heating, incubators, and just about anything electrical that needs athermostat to control it between the temperatures of -20 and 125°C. They

make use of small components called thermistors , which provide much

more accurate response to temperature change than traditional

mechanical thermostats.

Simple version 

Choose this circuit unless  you:

  Need especially tight hysteresis (or control range—see explanationbelow)

  Need to drive a heavier relay or other load that will draw more than

50mA

  Are powering it with small batteries  and want to minimise power

consumption

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The above circuit uses three fewer components than the one below,

thanks to the handy and unusual ability of the LM311 integrated circuit to

sink up to 50mA directly through its output. This means that no separate

transistor is needed for activating many common relay coils, such as

the SY4062  from Jaycar  that I've used.

The 311 is a purpose-built comparator chip (these circuits work

by comparing  a set voltage with a changing one produced by the

inversely temperature-sensitive thermistor). For this application, however,

it's a bit like using a Ferrari to do the work of a wheelbarrow. The 311 is

very sensitive and, unless significant feedback  is provided, stray electrical

noise will tend to make it oscillate (the relay will get jittery). In practice,

this means adjusting the VR2 trimpot to achieve a minimum of about 1°C

of hysteresis at 25°C (hysteresis is the interval between the points atwhich the circuit switches on and off, the range of control). One degree is

perfectly appropriate for most uses; but if you need a really tight

hysteresis zone, use the circuit below.

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Note that keeping all the left-hand-side resistors physically as close as

possible to the IC chip helps reduce stray noise.

This circuit draws about 3.5 to 4mA of current in the resting state, which

is peanuts in anyone's language, although the version below drawsaround 2mA (both measured using 16 volt supply—consumption will be

even less at lower voltages).

Versatile version 

Choose this circuit if you:

  Need especially tight hysteresis (or control range—see explanation

above)

  Need to drive a heavier relay or other load that will draw more than50mA

  Are powering it with small batteries  and need minimal power

consumption (see paragraph above)

The above version replaces the LM311 comparator with a

741 operational amplifier  integrated circuit acting as a comparator. It is

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less sensitive to minute disturbances and will allow hysteresis down to

0.5°C or less (at 25°C) without becoming jittery. It can also drive much

higher loads thanks to the use of a separate transistor (but see notes 2&3 

below ).

Instructions for both versions 

Cooling or heating? Both circuits are displayed as cooling thermostats.

But in both cases swapping the main inputs to pins 2 and 3 on the IC

(integrated circuit , triangle symbol) converts these designs into heater

control thermostats. If you do swap these two inputs for heater

control, don't swap the hysteresis feedback to the IC [always leave it

connected to the same pin as shown, i.e. pin 2 in the simple version  and

pin 3 in the versatile version ]).

Optionally, a double-pole-double-throw (DPDT) switch can be employed if

you want your thermostat to perform both heating and cooling control.

Wire the switch so that it acts as an intermediary, swapping the inputs to

IC pins 2 & 3, as described above.

Accessibility: Decide whether you want to use the thermostat as a

readily-adjustable device (like a wall thermostat) or as a single-

temperature, set-and-forget device. If the latter, a trimpot can be used atVR3, or a single trimpot (perhaps a 20k item) can be used in place of

both VR1 and VR3—although a single high-resistance trimpot will be

touchier to adjust.

Calibration: Start by setting VR2 to roughly the middle of its adjustment

arc. Then, assuming you are using two trimpots in series as per the

diagrams above, you will need to set the minimum temperature of your

desired adjustment-range with the VR1 trimpot. Do this by setting VR3 to

its maximum resistance, bringing the thermistor to the temperature youwant to use as the minimum, then adjusting VR1 so that the circuit trips at

that point. Next you can either set (if using a trimpot) or calibrate (if using

a potentiometer and panel-mounted dial) VR3. If calibrating a scale, it will

not be perfectly linear because of the thermistor's natural response curve,

so you'll need to mark off several points. Before firmly committing to

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either a scale or set-point, adjust the hysteresis trimpot, VR2, to provide

an effect that suits your application. This change might throw off your

scale or set-point slightly, so go back and check.

My unit, which matches the above diagram, is adjusted for a minimumtemperature of about 18° Celsius. The main 5k panel-mounted pot

extends the range up to about 28°C, marked in increments of one degree.

If you want a wider range, use a 10k pot at VR3. If you wish to use the

circuit for much lower or higher temperatures (the thermistor is rated for -

20 to 125°C), you can subject the thermistor to the target temperature

range extremes, measure its resistances with a multimeter, and plan out

your pot values accordingly. The thermistor has lower  resistance at

higher temperatures. Its rated resistance of 10k occurs at 25°C. At 30°C it

is more like 7k and at 17°C it's something like 14k. See note 6  below if

you want to work with much colder or hotter temperatures.

Warning: If you intend to use high voltage / household mainselectricity in conjunction with these circuits, make sure you complywith local laws. Do not attempt to work with mains power unless youare suitably competent or qualified. I take no responsibility fordamage or injury you might cause by electing to build, modify, oradd to these circuits.

Shopping: All parts used in these circuits should be readily available

around the world. Radio Shack in the US carries an equivalent thermistor,

for example, and possibly all the other parts too (or try Digikey —see

Postscript 3 below). Here in Australia, Jaycar  and Altronics , stock

everything. Dick Smith  only carry a 100k thermistor , which would suit a

modified circuit for higher temps (note 6 ), but last I heard they were

getting out of the components side of their business. Jaycar and Dick

Smith are in NZ too. Parts in yellow are used in the second 'versatileversion' circuit only.

Parts list

Component  Detail  Data Jaycar Cat Price

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Sheet  No.  approx,

AUD 

ICLM311 or

LM741 

PDF  

PDF  

ZL3311

ZL3741 

1.30

TransistorPN200 or similar

PNP typePDF   ZT2284 0.25

Diode IN4148 or IN914 PDF   ZR1100 0.32 / 5pk

R1,2,3,4 10k resistors 0.38?? / 8

R5 10k NTC thermistor PDF   RN3440 0.95

VR1 10k trimpot 0.32

VR2500k or1meg trimpot

0.32

VR3

5k linear

potentiometer (or

trimpot for set-&-

forget)

2.25 / 

(0.32)

$4-6 total

!! 

Extra components you might want

  A power supply such as a plug pack or battery. 12 volts will provide

easy compatibility with common relays, computer fans, bulbs, etc.

  A relay of some kind if you intend to switch high currents and/or

voltages (I chose Jaycar's  SY4062 ) 

  A piece of punched fibreglass board on which to build the circuit,

available in electronics supply shops. Alternatively, and if you havethe expertise, you can make a printed circuit board using the files

provided in the postscripts below.

  An 8-pin socket to suit the integrated circuit. For a few extra cents,

this protects the IC from soldering heat.

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  A housing of some kind. Jaycar  and Altronics  have great project

boxes if you're in Oz/NZ, otherwise electrical wholesalers carry big

plastic junction-box thingos that can be used.

  A front panel knob for the temperature-set pot.

  Optionally, a double pole-double throw (DPDT) switch will allow theunit to control both heating and cooling apparatus. See above,

under Heating or Cooling? .

Notes

1. The thermistor can be used as a remote probe. It can be encased

in silicone, epoxy, or something similar for applications where it will

be immersed in liquid.

2. In theory, this circuit should work with anything between 5 and 36volts DC. If you deviate too far from the middle ground of this

voltage range, however, you might need to tweak some of the right-

hand-side resistor values. I'm not sure. My circuits run at 16v,

employing a 150 ohm / 0.5w resistor in series with the relay coil to

drop the voltage to around the 12v it requires.

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3. Likewise, if using higher currents through the transistor to power,

say, a heavy-duty relay, solenoid, fan, or lamp, you might need to

reduce the value of R4 down to 5k, 1k, or lower to ensure that the

transistor remains saturated. The 10k item as depicted is known to

work with a relay coil drawing 50mA, so any coil requiring lesswould be covered too, provided your circuit voltage is not too much

lower than mine. In fact, the above also worked with R4 at 20k, so

there's some leeway built in. If your circuit doesn't work for you,

either consult some appropriate literature on configuring transistors,

or maybe try a 500ohm resistor at R4, and work your way up. When

the transistor is adequately saturated, the voltage at its collector

(the 'C' pin) should be near Vcc (the circuit's full positive voltage).

4. The maximum current available to power the relay, solenoid, etc,is dictated by the "Ic" rating of the PNP transistor chosen. Consult

the data sheets for your intended load device and transistor. The

PN200 used here will handle up to 500mA.

5. The diode protects the IC from damaging voltage spikes caused by

the collapse of the relay coil's field when it shuts off. Omit this

component only if you're powering something without a coil. If

powering a fan in equipment sensitive to radio noise, place an

electrolytic capacitor across the fan junction (say, 1000 microfarad).

6. If you intend to control much higher or lower temperatures, you

might want to consider using a thermistor better matched to your

target temperatures. The NTC (negative  thermal coefficient)

thermistor will have a much higher resistance in sub-zero

temperatures and much lower in, say, boiling water. A 4.7k or 1k

thermistor would probably be more appropriate for cold conditions;

a 47k item, at least, would better suit the hotter end of things

(remembering that these thermistors are physically rated for -20 to

125°C, so cryogenics and furnace work is out!). The point is tobalance the comparator's voltage seesaw (so that the resistance

feeding the "-" pin on the IC is similar to that feeding the "+" pin).

You might notice that these circuits, operating around the 25°C

point, use two resistors at the top-left that coincide with the

thermistor's resistance around that temperature (10k @ 25°C).

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Similarly, the temperature-control pots attempt to anticipate and

match the thermistor's resistance swing through the operational

temperature range. So if you know you will be working with more

extreme temperatures, buy a thermistor at least one step removed

in the series and you might be pleasantly surprised to find that theabove circuits need minimal or no modification. See the

thermistor data sheet  for options.

[Update] Ilija has kindly tipped me off to

this formula for calculating NTC resistance at a targeted

temperature (where T is in degrees Kelvin). He provides the

following example for 35°C: R(35) = 10000*e^4100(1/273.15+25 – 1/273.15+35) = 6350 ohm.

7. Optionally, you might like to calculate and modify your circuit's

expected hysteresis, and learn more about the Schmitt Trigger

concept that these circuits employ at this site . There you will find a

useful online calculator for key circuit values. Or you can refer to the

following Schmitt Trigger formulae (again, thanks to Ilija).

8. Powering the circuits with a battery: To calculate how long a

battery would last, you need to know how many 'milliamp-hours' it is

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rated at. This information should be provided by the manufacturer,

or you could look up ratings for a similar battery online. It is a

number expressed as mAhr, mAh, ma/hr, or something similar. A

large battery like a lead-acid car battery will be rated in amp-hours.

One amp-hour is a thousand milliamp-hours. Say you're buildingthe 'versatile version' circuit above, which draws 2mA, then a 2000

mA/h battery would last 1000 hours, or about 41 days. The 'simple

version' circuit would draw up to twice as much, so the same

battery would last maybe half as long. These currents were

measured with my 16 volt supply. Using a lower voltage will also

reduce the current draw significantly, so choose a 9v or 12v battery

and you will do yourself a favour. An ordinary 9v alkaline battery of

the type found in smoke alarms will be rated at something like 500mA/h. A rechargeable NiMH equivalent will only be 200 mA/h or

less. So neither will last for very many days, but the latter can be

recharged at least. A stack of six AA NiMH rechargeable camera

batteries in series, each typically rated at 2000 or 2500 mA/h, might

be a useful solution, although NiMH cells are only 1.2 volts each,

totaling 7.2v so see note (2) above. You can buy small 12v lead-

acid batteries from electronics or hobby suppliers for reasonable

prices. These come in all sizes. Here's one  from Jaycar, that gives

you 6000 mA/h for 28 bucks Australian. In theory it'd last something

like four months on the 'versatile version' circuit between charges

(although lead-acid batteries, like the one in your car, gradually go

flat over time even when they're doing nothing, so you'd probably

need to charge it a bit more frequently). A very small solar panel

hooked up to the battery would be perfect. If you have mains power

available, a 12v DC plugpack won't cost much and will provide an

easy solution. There's no reason to use a power supply with a

higher voltage unless you have an old plugpack or transformer lyingaround already (which is why I used 16v for mine).

9. By the way, your power supply's negative  is connected to the

ground or earth symbol (lower) side of the circuit...

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In conclusion 

Please don't be fooled by the above into thinking that I know heaps about

electronics. This has been a collaborative effort with the people listed

below. If you have really serious technical questions, there's probably no

point contacting  me; but I'd be very pleased to hear any stories ofsuccess and obscure / creative uses.

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Postscript 1 

Ilija has very kindly provided a few files detailing his reportedly successful

prototype adaptation of the LM741 circuit above. He has incorporated a

simple mains / 10 volt power supply into the circuit which drives a TIC226

triac load. Many thanks Ilija!

Note that the power supply portion of Ilija's circuit contains an error. The

BZV10 is actually rated at 6.2V, not 10V. Ilija's intention was to use any

10V zener diode. Alternatively, he suggests a 7810 voltage regulator

instead of the zener, which will provide for more stable voltage.

Note also that I have not tested these variations myself and cannot vouch

for their effectiveness. I presume that the PCB design would have to be

slightly modified for a 7810, for example, and I see that the layout in the

top picture does not quite match the photograph.

Eagle format printed circuit board  (5kb) 

Eagle format schematic  (29kb) 

Browser image schematic  (40kb)

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Postscript 2 [October 2009] 

A huge thank-you to Andrew, who has shared his PCB design files and

notes for a caravan refrigerator controller. He found that the fridge's

existing temperature regulation wasn't up to scratch, and my circuit

brought things under control nicely. He has included an onboard filteredpower supply for 12 volts and a LED indicator. Andrew has had his board

produced by a commercial manufacturer, and it definitely works. Click

these images for enlargements or see the Eagle files below:

Eagle format printed circuit board  (24kb) 

Eagle format schematic  (277kb) Explanatory notes in PDF format (33kb) 

Explanatory notes in Word format (54kb)

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Fan control temperature using sensor LM35

Basic circuit of the LM35 are made to control the fan is either used on amplifier that requires automatic cooling.

Its use on power amplifier circuit above and only requires DC fan. From basic sensors based on ic and

amplifier op-amp is added again to the transistor Q1 to drive the fan.

Part List :

R1___220K

R2___100K

R3___3K3

R4___22K

R5___1M

R6___150R

R7___2K2

R8___33R 4W

C1___100pF

D1___1N4148

IC1__7915

IC2__TL072

IC3__LM35

F1___DC Fan 12V

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In many times in some audio applications or other electronic

applications we need a fan controller to keep the temperature of some

elements from circuit on a constant temperature or just to keep the

device at low temperature .

In many applications we need to cooling the heatsink or ventilate the

air inside the device . With this fan controller circuit from this

schematic we can make an automatic ventilation .

For this electronic fan controller circuit we need just few cheap and

common electronic components .

The fan controller circuit schematic presented in this sheet is build

using a 741 operational amplifier , one thermistor and other few

components .

This fan control ( fan cooling ) circuit will control a 12 volt fan with

maximum current required around 200 mA.For sensing the temperature is use a #271-110 thermistor which turns

the fan on when the temperature exceeds 31 degrees C.

If you would like to turn the fan on at a different temperature you can

replace the 8.2K resistor ( R4) with a 10K trimmer pot.

For this fan cooling controller circuit you can use a power supply with

a output voltage between 12 and 15 volts dc .

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Small-scale atmospheric circulation is the hot water boiler heating to forced

circulation by pump. Burned when boiler water temperature about 85 ℃, theneed to manually start the pump, so water began circulating heat exchange;

when the cycle of water temperature gradually dropped to about 50 ℃, the  

need to manually turn off the pump, stop the water cycle, continue to burn

boilers; until the water temperature rose again to 85 ℃, and then manuallystart the pump to cycle. Kotelshchik need to always check the boiler

temperature, and then decide whether to start and stop the pump, so as not toboil the water inside the boiler caused by increased pressure within the heating

system safety hazard.

This example describes the atmospheric pressure boiler automatic temperature

controller that enables the boiler water temperature reaches 85 ℃ startautomatically when the pump work, the water temperature dropped to 50 ℃,the pump shut down automatically.

Circuit Work The atmospheric pressure boiler automatic temperature controller circuit consists

of power supply circuit, the temperature detection control circuit, trigger circuit

and control the work of the implementation status indication circuit, as shown.

Temperature detection control circuit by the temperature sensor RT, resistors R1

~ R5, potentiometer RP1, RP2, and operational amplifier integrated circuit IC1

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(N1, N2) components.

Trigger NAND gate integrated circuit by four internal NAND gate IC2 D1 ~ D4

composition.

Control the implementation of the circuit by the resistor R7, transistors V, diode

 VD and relays K composition.

Working status indicator circuit consists of current limiting resistor R6 and the

light-emitting diodes composed of VL.

Power circuit from the power switch S, the power transformer T, rectifier bridge

pile UR, three-terminal voltage regulator integrated circuit IC3 and filter

capacitors C1, C2 composition.

Turn the power switch S, AC 220V step-down voltage by T, UR rectifier, C1 filter

and voltage regulator IC3, the two ends of the C2 +5 V voltage supply

temperature detection control circuit, trigger and control the implementation of 

the circuit.

Temperature sensor and resistor R1 form RT temperature detection circuit;

potentiometer RP1 and resistors R2, R3 form the lower temperature limit setting

circuit; RP2 and M, R5 form the upper temperature limit setting circuit.

 Adjusting the resistance of RP1, you can make A point (N1 op amp inverting

input) voltage varies between 1.74 ~ 2.29V; adjust the resistance of RP2, can

make the B (N2 op amp inverting input) voltage varied between 2.53 ~ 3V.

The resistance temperature sensor RT decreases with increasing temperature.

When the boiler water temperature exceeds a set temperature of the upper limit

(eg 85 ℃) when, C point (M inverting input terminal and the N2 of the positive

phase input terminal) voltage will b

e higher than the B point voltage, N2 output high so that the output of D flip-flop

goes high point, V full pass, K pull its normally open contact connected through

the exchange of contacts (circuit not shown) to pump the work of the power-on,

pump starts running, so that hot water to start the cycle. With the decline in

water temperature, RT increases the resistance, so that gradually reduce the

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voltage of C points. When the water temperature below the set temperature, the

lower limit (eg 50 ℃),, C point voltage will be lower than the A point voltage,N1 output high level, so that point D goes low, V cut-off, K release, water pumps

stop operation.

Start the pump running, VL light; the pump stops working, VL off.

Component selection

R1 ~ R7 selected 1/4W carbon film resistors or metal film resistors.

RP1 and RP2 are made of a linear potentiometer.

RT NTC negative temperature coefficient selected thermistor (temperature is 5k).

C1 and C2 are selected voltage is 16V aluminum electrolytic capacitors.

 VD use 1N4148 silicon switching diodes.

3mm or 5mm VL use light-emitting diodes.

UR chosen 2A, 50V rectifier bridge heap.

 V use 58050 or C8050, 3DC8050 silicon NPN transistor.

IC1 LM324-based selection of quad op amp IC; IC2 use or CC4011 CD4011

NAND gate integrated circuit type four; IC3 use LM7805-type three-terminal

integrated voltage regulator.

T use 3 ~ 5W, the second voltage is 9V power transformer.

K selection JQX-14FF-type or 4098 Series 5V DC relay.

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 You are here: Home> schematics> control circuit> temperature control circuit

NE555 constitute breeze ceiling fan temperature controller circuit time :2008-09-

21 11:50:39Figure shows the breeze ceiling fan temperature control circuit. It consists of 

temperature control circuit and the step-down rectifier power circuit. The control

circuit power supply circuit which provides DC voltage VDD = 5V. The core

temperature control circuit for the IC (555) and R5, R7, W1, R6 and other

components of the bistable flip-flop, and, R6, R7 NTC thermistor used as

temperature measurement devices.

When the ambient temperature increases, the corresponding R6, R7's resistance

becomes smaller, the IC potential decreased due to less than â‘¡ 1/3VDD feet

were set, 3 pin output high. So that the D2 ~ D5, SCR, BG1, BG2 and othercomponents of the SCR AC switch is zero pressure, the fan power and running

for D; when the ambient temperature decreases, the corresponding R7, R6

larger the resistance, â‘¡ 555 feet because of potential increased to more than

1/3VDD be reset, â‘¢ pin output low, so that the exchange of zero -voltage

switching SCR off, disconnect the power supply fan D stopped by.

When debugging, you can set the temperature points as needed. When the

ambient temperature is higher than the set temperature, the fan automatically

open; when the ambient temperature is below the set temperature, the fan from

the stop. Stability for the adjustment potentiometer potentiometer W1,corresponding to the temperature dial can be marked.

Top click 

Temperature controller circuit works: This example describes the intermittent

controller can automatically control the electric heaters, humidifiers, electric set

the single-phase AC motors, so that in intermittent working condition.

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The controller circuit consists of intermittent power supply circuit, timer and

control the implementation of circuit, as shown.

Component selection

R1 ~ R4, R6 and R7 are selected 1/4W metal film resistors: R5 are selected

1/2W metal film resistors.Selected monolithic capacitors C1; C2 use the CBB capacitor voltage is 450V; C3

use of electrolytic capacitors voltage is 16V; C4 voltage is 25V with aluminum

electrolytic capacitors.

Type 1N4001 silicon rectifier diode VD1 use; VD2 ~ VD4 are selected 1N4148

silicon switching diodes.

 VS selection 1N4742 (1W, 12V) silicon voltage regulator diodes.

LEDs use φ5mm VL. UR selected 1A, 100V rectifier bridge heap.

 V S8050 or use C8050, 3DG8050 silicon NPN transistor.Or CC4060 CD4060 IC type used 14-bit binary counter / divider integrated

circuit.

4098 K-type 12V DC relay selection.

KM use 220V AC coil voltage contactors, the contact current capacity should be

based on the actual load power to choose.

Power supply circuit by the capacitor C2 ~ C4, resistor R3 ~ R5, rectifier bridge

pile UR, Zener diode and the power indicator LED VS VL composition.

Timer circuit consists of counting / divider integrated circuit IC, capacitor C1,

diode VD2 ~ VD4 and resistors R1, R2, R6 composition. In which R1, R2, C1 andIC clock oscillator circuit within the circuit, the oscillation period (T) R2 and C1 by

the value of the decision.

Control the implementation of the circuit by the transistor V, resistor R7, diode

 VD1, AC contactor relays K and KM composition.

 AC 220V step-down voltage by C2, UR 

rectifier, VS regulator, R5 and C3-limiting filter, the relay K and the IC to provide

12V DC voltage, while VL lit.IC power work, the clock oscillator and the oscillation frequency count signal

processing, when the time delay on time (waiting time) at the end, IC of the Q14

side (3 feet) high output, so that V conduction , K, and KM pull, the load (the

controlled setting of the power) the power supply connected. At the same time,

IC has started regular working hours (working movement time) are counted,

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when the end of regular working hours, IC of the Q14 side goes low, so that V

cut-off, K and KM release, load power; the same time IC internal counter is

reset, the next time cycle. Again and again, the load at the set time

intermittently energized work.

 Adjusted R2, C1 or change the parameters of IC's Q4 ~ Q14 output controlconnection, you can set the delay on-time and regular working hours. By the

circuit parameters, the delay Turn-on time 3h, regular working time is 20min.

Circuit diagram

Parts:

  P1 22K Linear Potentiometer (See Notes) 

  R1 15K @ 20°C n.t.c. Thermistor (See Notes)

  R2 100K 1/4W Resistor

  R3,R6 10K 1/4W Resistors

  R4,R5 22K 1/4W Resistors

  R7 100R 1/4W Resistor

  R8 470R 1/4W Resistor

  R9 33K 4W Resistor

  C1 10nF 63V Polyester Capacitor

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  D1 BZX79C18 18V 500mW Zener Diode

  D2 TIC106D 400V 5A SCR

  D3-D6 1N4007 1000V 1A Diodes

  Q1,Q2 BC327 45V 800mA PNP Transistors

  Q2 BC337 45V 800mA NPN Transistor

  SK1 Female Mains socket

  PL1 Male Mains plug & cable

Device purpose:

This circuit adopt a rather old design technique as its purpose is to vary the

speed of a fan related to temperature with a minimum parts counting and

avoiding the use of special-purpose ICs, often difficult to obtain.

Circuit operation:

R3-R4 and P1-R1 are wired as a Wheatstone bridge in which R3-R4

generates a fixed two-thirds-supply "reference" voltage, P1-R1 generates a

temperature-sensitive "variable" voltage, and Q1 is used as a bridge

balance detector.

P1 is adjusted so that the "reference" and "variable" voltages are equal at a

temperature just below the required trigger value, and under this condition

Q1 Base and Emitter are at equal voltages and Q1 is cut off. When the R1

temperature goes above this "balance" value the P1-R1 voltage falls below

the "reference" value, so Q1 becomes forward biased, pulse-charging C1.

This occurs because the whole circuit is supplied by a 100Hz half-wave

voltage obtained from mains supply by means of D3-D6 diode bridge

without a smoothing capacitor and fixed to 18V by R9 and Zener diode D1.

Therefore the 18V supply of the circuit is not true DC but has a rathertrapezoidal shape. C1 provides a variable phase-delay pulse-train related to

temperature and synchronous with the mains supply "zero voltage" point of 

each half cycle, thus producing minimal switching RFI from the SCR. Q2 and

Q3 form a trigger device, generating a short pulse suitable to drive the

SCR.

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Notes:

  The circuit is designed for 230Vac operation. If your ac mains is rated at

about 115V, you can change R9 value to 15K 2W. No other changes are required. 

  Circuit operation can be reversed, i.e. the fan increases its speed as

temperature decreases, by simply transposing R1 and P1 positions. This mode of 

operation is useful in controlling a hot air flux, e.g. using heaters.

  Thermistor value is not critical: I tried also 10K and 22K with good results.

  In this circuit, if R1 and Q1 are not mounted in the same environment, the

precise trigger points are subject to slight variation with changes in Q1

temperature, due to the temperature dependence of its Base-Emitter junction

characteristics. This circuit is thus not suitable for use in precision applications,

unless Q1 and R1 operate at equal temperatures.

  he temperature / speed-increase ratio can be varied changing C1 value. The

lower the C1 value the steeper the temperature / speed-increase ratio curve and

vice-versa.

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Parts List: 

R1 = 560 ohm Q1 = 2N2907 (NTE159M) low

noise

R2,R9 = 100K Q2 = MJE521 (NTE184)

R3,R8 = 10K IC1 = 741, op-amp

R4,R7 = 1K Led1 = LED, red

R5 = 470 ohm D1,D2,D3 = 1N4148, signal diode

R6 = 100 ohm, 2watt, wire-wound D4 = 1N4004, general purpose

diode

P1 = 100K, trimmer pot

C1 = 2.2uF, 25V, electrolytic

C2 = 47uF, 25V, electrolytic

This circuit controls very accurately a fan of any size. Just adjust the associated

resistors for a different type like the R6 resistor of 100 ohm, 2 watt type and you're all

set. The above circuit diagram is for a small 12 volt fan, the size and type determined

by the user.

Temperature is sampled via the 1N4148 diodes and presented at pins 2 and 3 of the

differential type 741 op-amp. R7 (10K) is used to create a voltage difference between

the inverted and non-inverted input pins 2 and 3 of the 741. All signals presented at

pin 2 will be inverted on the output pin 6. Obviously then, the input pins are very

important. When pin 2 goes more positive than pin 3, the output pin 6 of the 741 goes

high and forward biasing the base of transistor Q1, which switches on transistor Q2

and the Led and puts 12V on the output pins for the fan. R9 functions as a feedback 

for the 741. Only DC type fans can be used with this schematic diagram without

further modifications.

The temperature sensor is made up of three easily available 1N4148 signal diodes

mounted in parallel. Mount them in a thin aluminum, or plastic tube (depending on

your application) and silicon the end of the tube to make this temperature sensor

water-proof. As an additional note, I have seen this type of temperature sensor, with

the diodes either in parallel or series and either 1 or more diodes, in all sorts of 

laboratory equipment like hot water baths and others. The water bath temperature

setting ranged from room temperature to about 100° Celsius. Keep in mind that using

the 1N4148 diode as a temperature sensor is very accurate when used within the

specifications of the 1N4148.

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Fancontrol electronic circuit diagram

R1 15k ohm resistor NTC Thermistor- 10k ohm, sold at Radio Shack in the states. P1 10k ohmpotentiometer - sets the low speed(voltage) of the fans at the cool temperature. P2 50K ohmpotentiometer - sets the gain of the circuit - how fast the voltage will rise to full output when the temp

is higher. TL082 a op-amp that I had handy, most any single voltage op-amp should work. The TL082is a dual op-amp if you want more then one controller on a board. note that the power and groundconnections for the op-amp are not shown on the schematic. R2 - The TL082 is a fast op-amp, neededR2 to reduce oscillation. IRF-510 A 4 amp mos-fet in a TO-220 case. Bascially as the voltage on thegate rises the mos-fet will conduct more current. note 1 there are also IRF-520 and 530 versions thatwill handle more current. note 2 Even at 5 watts the mos-fet will disapate some heat and will need tobe heat-sinked or at least in the air flow path. the large metal part of the fet will be at drain(D)voltage level. Do not attach to case. D1, almost any diode, 1N4001 should work,it conducts backaround the fan when the mos-fet turns off. As the fan continues spinning it will produce a voltage onthe drain lead of the fet. D1 will limit that voltage. Adjustment, easiest if you have a voltmeter but canbe done without. Get the thermistor at room temp. Adjust P1 for the low speed that you want yourfans to run at. Heat the thermistor to the high temp you want the fans at full speed. ( I stuck it undermy tongue) Adjust P2 until the fans are at full speed( with voltmeter the highest voltage you can get)then adjust P2 until the speed/voltage just begins to drop off. Most fan specs that I have seen show a

low voltage limit of around 7 volts. Some of the smaller 80mm fans have a lower limit of 8 volts. If you set the low voltage to low the fans may stall until the thermistor heats up enough. Let me know if you build this circuit and how it works for you. corrected, single voltage op-amps should be used, OP-07 is a dual voltage. 

. MJE1100

1243. MJE1101

1244. MJE1102

1245. MJE1103

1246. MJE2100

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1247. MJE2101

1248. MJE2102

1249. MJE2103

1250. MJE521

1251. MJE5740

1252. MJE5742

1253. MJE800

1254. MJE800T1255. MJE801

1256. MJE801T

1257. MJE802

1258. MJE802T

1259. MJE803

1260. MJE803T

50K Thermistor Output Ta

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Thermistors

THERMal resISTORS

Thermistors are special solid temperature sensors that behave like temperature-sensitive

electrical resistors. No surprise then that their name is a contraction of "thermal" and

"resistor". There are basically two broad types, NTC-Negative Temperature Coefficient,

used mostly in temperature sensing and PTC-Positive Temperature Coefficient, used

mostly in electric current control.

There's even more history of the name and development of thermistors and facts about

some key NTC parameters at the Kele Electronics website, just be prepared for some

strong opinions about one brand of thermistor.

They are mostly very small bits of special material that exhibit more than just temperature

sensitivity. They are highly-sensitive and have very reproducible resistance Vs.

temperature properties.

During the last 60 years or so, only ceramic materials (a mix of different metal oxides)

was employed for production of NTC thermistors. In 2003, AdSem, Inc. (Palo Alto,

CA) developed and started manufacturing of Si and Ge high temperature NTC thermistors

with better performance than any ceramic NTC thermistors.

Thermistors, since they can be very small, are used inside many other devices as

temperature sensing and correction devices as well as in specialty temperature sensing

probes for commerce, science and industry.

Some of those new-fangled digital medical thermometers that get stuck in one's mouth by

a nurse with an electronic display in her other hand are based on thermistor sensors. They

are probably inside your cell phone, automobile, stereo and television, too, but you'd

never know it unless you were an engineer or visited here.

Thermistors typically work over a relatively small temperature range, compared to other

temperature sensors, and can be very accurate and precise within that range, although

not all are.

Thermistor Terminology

A glossary slightly modified from that given in a US government publication: MIL-PRF-

23648D. Note that the term being described is in bold typeface.

A thermistor is a thermally sensitive resistor that exhibits a change in electrical

resistance with a change in its temperature. The resistance is measured by passing a

small, measured direct current (dc) through it and measuring the voltage drop produced.

The standard reference temperature is the thermistor body temperature at which

nominal zero-power resistance is specified, usually 25°C.

The zero-power resistance is the dc resistance value of a thermistor measured at a

specified temperature with a power dissipation by the thermistor low enough that any

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further decrease in power will result in not more than 0.1 percent (or 1/10 of the specified

measurement tolerance, whichever is smaller) change in resistance.

The resistance ratio characteristic identifies the ratio of the zero-power resistance of a

thermistor measured at 25°C to that resistance measured at 125°C.

The zero-power temperature coefficient of resistance is the ratio at a specified

temperature (T), of the rate of change of zero-power resistance with temperature to the

zero-power resistance of the thermistor.

A NTC thermistor is one in which the zero-power resistance decreases with an increase

in temperature.

A PTC thermistor is one in which the zero-power resistance increases with an increase in

temperature.

The maximum operating temperature is the maximum body temperature at which the

thermistor will operate for an extended period of time with acceptable stability of its

characteristics. This temperature is the result of internal or external heating, or both, and

should not exceed the maximum value specified.

.

The maximum power rating of a thermistor is the maximum power which a thermistor

will dissipate for an extended period of time with acceptable stability of its characteristics.

The dissipation constant is the ratio, (in milliwatts per degree C) at a specified ambient

temperature, of a change in power dissipation in a thermistor to the resultant body

temperature change.

The thermal time constant of a thermistor is the time required for a thermistor to

change 63.2 percent of the total difference between its initial and final body temperature

when subjected to a step function

The resistance-temperature characteristic of a thermistor is the relationship between

the zero-power resistance of a thermistor and its body temperature.

The temperature-wattage characteristic of a thermistor is the relationship at a

specified ambient temperature between the thermistor temperature and the appliedsteady state wattage.

The current-time characteristic of a thermistor is the relationship at a specified ambient

temperature between the current through a thermistor and time, upon application or

interruption of voltage to it.

The stability of a thermistor is the ability of a thermistor to retain specified characteristics

after being subjected to designated environmental or electrical test conditions.

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