Constant Current LED Driver With PWM

This is a constant current LED driver which runs from 12V and it also encorparates PWM dimming

NE555 (1 piece)

small signal transistors (6 pieces) (for 3 series LED pair)(it can 2n222 or BC547 I've used 2N2222 and 2SC1815)

1Watt power LED (depending upon color and series LED pairs I've used 13 LED)

1kΩ resistor (4 pieces)

330Ω resistor (1 piece)

50kΩ potentiometer (1 piece)

Diode (2 pieces) (I've used 1N4001 but you can use 1n4148 or similar)

Medium power PNP transistor (I've used A940 but you can use BD140 or any PNPN transistor with at least 1A current rating)

10nF ceramic capacitor (2 pieces)

100uF electrolytic capacitor (1 piece)

Current setting resistor (3 pieces for 3 series LED pairs)

This circuit consist of 2 section constant current section and PWM section

Constant current section:

This is simple current regulator based on 2 transistor upper transistor acts a variable resistor on its emitter there is a current sense resistor when its voltage drop around 0.6V - 0.7V the lower transistor starts to conduct steal some current from upper transistor which limits the collector current of upper transistor and current is regulated. The current formula is 0.65/ Rsense = I. I've used values around 7Ω which gives around 100mA (this LEDS rated for 300-350mA). Because of this LEDs run cooler don't require much heatsinking. when I was bulding this light, I didn't have 1 Watt LED heatsinks so I soldered some thick wires to their heatsink pads to spread their heat easily. Mechanical design of the light is awful (it is hanging above the desk without any light spreading but it is working more than 6 months)

PWM section:

NE555 runs in astable mode and it is producing PWM at arond 3kHz with adjustable duty cycle depending upon the potentiometers posistion. Then this PWM signal drives PNP transistor, so you can dim LEDs from 100% to 6-7% brightness

Some notes

You can change the current by changing sense resistor but over 150mA you heatsink LEDs properly otherwise their lifespan will significantly reduced and also if you go over 200mA check power dissipation of the upper transistor at the constant current section. If you want more current replace 2N2222 with BD139 or similar and use heatsink (if necessary)

This is a approximately 3.5 watt light (at full power it draws around 300mA-350mA from 12V) and it is almost monochromatic. Replace LEDs at your requirement (forward voltage of the series LED pair has to lower than supply voltage)

You can add these pairs parallel if you want but at higher currents replace PNP transistor with P-channel MOSFET it wold dissipate less power.

Waveform seen by one the LED pairs