I want to use WS2811 to drive high current LEDs. As it is mentioned in the datasheet this chip provides 3 channels with 18.5mA constant current sinks. Maybe what I need is a simple PNP BJT with constant amplification factor of 18 (18.5*18=333mA for 1W LED) like the circuit below
simulate this circuit – Schematic created using CircuitLab
But I know there is no such BJT with fixed beta. Is there any simple circuit that can do just that? (I'm just a hobbyist, excuse me for any mistakes)
It is possible to use the current-limited outputs to drive higher currents into large LEDs, by use of a current-mirror amplifier
simulate this circuit – Schematic created using CircuitLab The transistors should be heatsinked, if possible, to keep similar temperatures; the 2N3906 probably can't handle this job, a higher power PNP would be recommended. R1 can be adjusted according to emitter resistance of the chosen device to tune the current gain.
Just do it correctly and use an LED driver with the current rating you desire.
TI $0.40 LM3401 with a $1 BOM would be a simple inexpensive choice. 93% efficiency.
No this won't work effectively because you'll force much more than 333 mA into the LED. The base will be dragged down towards 0 volts by the open collector driver and the emitter will follow 0.7 volts behind. What you need to do is form a potential divider so that the base is at about 1.1 volts below the positive 12 volt supply when activated by the output. This forces about 0.3 to 0.4 volts across the emitter resistor which then dictates the current flow.
If your LEDs are actually 3 volt types (as implied by the power rating of 1 watt) then you can make the 1 ohm resistor bigger in value and gain more control but, whichever way you cut it it, there is going to be 9 volts dropped between transistor and emitter resistor and this is going to dissipate 9 x 0.333 watts = 3 watts i.e. more than the diode itself.
Maybe these LEDs are not well suited to this driver?
