Introduction to Prototyping a LED Driver

Part I: Driver Design and Component Selection

September 24-28, 2012Carol Lenk

PCB Prototyping ProcessDesign

PCB Layout Software

Schematic Capture

Layout

Manufacturing (Gerber) Files

Bill of Materials (BOM)

PCB-top copper.gbrPCB-top mask.gbrPCB-top silkscreen.gbrPCB-bottom copper.gbrPCB-drill data.drl

Layout Software Options• Low Cost – Eagle

– $69, 2-layer PCB, 100mmx80mm– Steep learning curve, uses scripts.

• PCB Manufacturer Provided – PCB Artist– Can’t import or export, must order from 4pcb.com.– Can get gerbers after one PCB order.

• Freeware – DesignSpark– Functionally similar to PCB Artist, but can generate gerbers.– Easy to use graphical interface.– No

Boost SMPS

•Vin < Vout•Vin max 6V.•Vin always connected to L1.•Internal transistor ON pulls SW to GND. Thus L1 current goes up, D1 is off.•Transistor OFF pulls SW above FB to turn on D1 to power LEDs and causes L1 current to go down.

Our book uses this circuit in a example converting 2D batteries (2.4V) to drive a single power LED (3V).

Practical DC Drive Circuitry for LEDs. Lenk, Ron and Carol. “Practical Lighting Design with LEDs.” Wiley, 2011.

AC ExampleOur book uses this circuit in a example BR40 self ballasted light bulb design.

•Supertex HV9910 uses external MOSFET Q1. Current controlled Buck converter.•R2 sense resistor sets current.•R1 sets the switching frequency.•When Q1 is on, D1 is off, L1 current increases.•When Q1 is off, D1 turns on, L1 current decreases.•Vin can be up to 450VDC, usable worldwide.

HV9910 Demo Board

The HV9910DB3v.3 can supply a maximum output

current of 900mA to drive LED strings from a 9VDC to

30VDC input. It achieves an overall efficiency above

85%. The HV9910DB3v.3 is ideally suited to drive two

1Watt or 3Watt LEDs from a 12V or 24V input voltage.

Demo Board Schematic

Bill of Materials (BOM)

• Tolerance not an issue.• Narrow down by Operating Temperature, Min

Qty, Click on up-arrow under Price:490-5520-1-ND

Surface Mount Packages

Resistors

• Search: Resistor. Select: Chip Resistor-Surface Mount.• Select: 147 K, 1/10 W.• Select: Cut-tape.• 0805 is $0.86, 0603 is $0.10: P147KHCT-ND

Remaining Component

• Search: Schottky Diode. Select Diodes, Rectifiers, Single.• Select 40V, 1 A, SM. Sort by price: 641-1015-1-ND

• Search: Power Inductor. Select: Inductor, Coils, Chokes – Fixed.• Select 220 uH, 1 A, Shielded: 513-1424-1-ND

• Search: MOSFET N-Channel. Select: FETs, Single.• Select 50 V, 2.4 V to 15 V. Sort by price, pick SM: RFD14N05LSM-ND

• Search: HV9910. Select: PMIC – LED Drivers.• Pick no heat pad: CLA320CT-ND

Digikey Order

Thank You