This is a schematic of the circuit shown earlier. You see that the input rectifier and EMI filter are very similar to a power supply design with a constant output voltage. In fact, they are identical to what is used on the VIPer12 power supply designs. On the board shown here, the VIPer12, which is the primary side controller and the TSM103, is doing the current sensing, and providing the feedback across the output coupler and a rectifier diode. This configuration is very similar to a power supply. The main difference is we are using a TSM103 instead of a voltage sensing circuit like a TL431. Because we are sensing the current with this configuration, we can provide a range of output voltage to drive different output configurations of the LEDs in series. Since the output voltage and the auxiliary voltage that supplies the Vdd to the VIPer are related by the turns ratio of the transformer windings, the output voltage range, and therefore the number of LEDs in series, is limited by the allowable operating voltage range of the Vdd on the VIPer and the turns ratio of the transformer between the output and auxiliary windings. The other limit on the number of LEDs that can be driven is the maximum power that can be delivered by the VIPer. For the VIPer 12, the maximum power for a universal mains configuration is 6 watts. It should be noted that this board is capable of driving output currents of 350 milliamps, 700 milliamps, or 1.05 amps by selecting the jumpers on the board. So we can easily accommodate either 1 watt LEDs at 350 milliamps or the 3-watt LEDs at 700 milliamps.