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Author Topic: Crit my TLC5940-Luxeon high current driver circuit  (Read 1041 times)
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Hi alls,

I'm using the TLC5940 as a control source for a Luxeon.

This is the circuit I've come up with:

I've breadboarded and it seems to work just fine (I think the 220[ch937] values on R4/5 should be lower though, it doesn't leave much voltage across R2).

The right hand part of the circuit comes from the Circuits for using High Power LED's Instructable The left hand part (Q3, Q4, R4, R5) is a current mirror that was conceived with help from the Eng-Tips forums The challenge here was to separate the PWM part of the TLC's functionality from the constant-current part, and this was achieved by mirroring the current. R2 converts the mirrored current into a ~+5V voltage input for the Instructable circuit.

All grounds should be connected together, including the TLC5940's. +V1 should be 5V, +V2 can be anything up to the maximum that the MOSFET Q2 can take. For more info on Q2 and for setting R3 see the Instructable.

Thoughts? I know it's a bit more elaborate than it could be, but I needed to be able to run the other TLC5940 pins at ~20mA for ordinary LEDs, and I couldn't figure out how to set the current mirror ratio reliably so just left it at 1:1.

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