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There are a couple of different supply voltages that are common for LED drive. One of them is the off-line solution, connected directly to the mains. In this case, we can use the same devices that we use to build off-line power supplies and change the output configuration so that we are delivering a constant current output as opposed to delivering a constant voltage output. If we look at the circuit for that board it’s the same configuration that we have for a standard power supply on the front end. This particular device uses a VIPer12 which contains the PWM, the power stage, and all of the control circuitry for the front end of the power supply. The rectifier and the EMI filter would be exactly the same as we would use for a similar power supply of the same basic power level, if we were doing a constant output voltage supply. The main difference is on the output side. In this case, you can see that we have changed the output configuration from sensing the output voltage to sensing the voltage drop across a current sense resister in series with the LEDs, so we are regulating the current through the LED string.
