Apr. 13, 2010 at 10:49pm
This is how to use the TLC5940 (or any other constant-current LED PWM driver) with Luxeon/Cree high-power LEDs. 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 then converts the current into a voltage input for the Instructable circuit. All grounds should be connected together, including the TLC5940’s. +V1 should probably 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 Circuts for using High Power LED’s Instructable.

This is how to use the TLC5940 (or any other constant-current LED PWM driver) with Luxeon/Cree high-power LEDs. 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 then converts the current into a voltage input for the Instructable circuit.

All grounds should be connected together, including the TLC5940’s. +V1 should probably 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 Circuts for using High Power LED’s Instructable.