High Current Flickering Pumpkin LED Driver

Step 2 Circuit Design

The Tea Light produces the pseudo random flickering flame simulation by varying the voltage and current of the LED. The Tea Lights LED (+ Anode Lead) output drives the current of the BJT transistors making the output LED's flicker. To make the output LED's flicker you need to adjust the variable resistor R1 and R2 to a position as not to saturate the transistors output
but to make LED's flicker like the Tea Lights LED. A good starting point for R1 is 50K ohms and R2 is 20K ohms. The Output LED driver 2N3906 has a maximum IC of 200mA and that can be replaced with PN2907 for a maximum IC of 800mA.
The resistor Rx can be changed to control the current and voltage through the output LED's. I used 471 ohms for Rx to produce a maximum current of 25mA in each LED.
You can install many output driver sections together to produce more lumens of flickering light.

The circuit design makes a simulated candle flame effect to drive high current LED's, other high current loads, or HBLED, etc.

Comments

[Paddy21]

Are you sure the Tea Light varies the voltage and current? I would sooner believe it creates a psuedo random PWM output to the LED. Meaning, it turns on the LED for random amounts of time. I can't see from the picture what exactly makes up the Tea Light circuit to say one way or the other though.

[Hillhiker]

I have been looking for something like this for a while... this seems to be a very nice approach to the flickering LED problem in that the lumen's or volume of light if you will can be adjusted... also no PIC and ATMEL devices need to be dealt with... wondering how a couple Cree-XR's would look... breadboard time... Thanks

[corey872]

Neat circuit. The latest round of tea lights I bought, the 'flicker' was built right into the LED as opposed to being a separate circuit board as with the older designs. But this should work just about the same. I've used a very similar circuit and some 150mA 'straw hat' LEDs (ebay) to really light up some pumpkins. With the LEDs is you can light up plastic, foam, and all manner of otherwise 'flammable' pumpkins and decorations. Though I also have to have several real pumpkins with candles...just have to have the 'burning pumpkin' smell in the crisp fall air to really feel like Halloween! On a side note, experiment with the variable resistors, then swap out for cheap/small fixed resistors of the same value to really miniaturize the circuit.