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I'm using the demo board for the NCP1012 with a few modifications. I've changed the transformer, output capacitor and zener to deliver 30 volts at 3 watts. I've got a couple of questions. First, I'm driving a large output capacitor (4700 uF) that is needed for energy storage in the event of line loss. The modified demo board will charge it up but it takes about 10 seconds. I assume that the problem is the controller's overload detection being activated. Are there any tricks to getting that bulk capacitor charged up quicker? My second issue is that I believe I'm damaging the controller when I pull out the power cord (sudden line loss). I'll have it running delivering about 50 mA to my load and then I'll yank out the power cord, The next time I power up and apply my load the voltage on the large storage capacitor drops suddenly by about 5 volts and then gets back to 30 volts. It's like the board's frequency response is significantly worse. If I put in a new controller, plug in the power cord, let the output capacitor charge to 30 volts then apply my 50 mA load, there's no noticeable drop in the voltage of the large storage capacitor. Any thoughts as to how I'm apparently damaging the controller?

It is possible that NCP1012 triggers an overload condition at the start up. The capacitor acts as a short at the very beginning. The charging current asymptotically approaches zero as the capacitor becomes charged up to the output voltage.

Can you provide the application schematic, transformer details, scope plots of the drain, FB and Vcc? Contact us here: Technical Questions

I would suggest the design of off-line constant voltage, constant current (CVCC) power supply like is described in our Application Note: A Simple Secondary Side Vcc Source for Low Power, Constant Voltage, Constant Current (CVCC) Power Supplies where you can control the maximum load current and output voltage.
Answered by:
ON Semiconductor
2013-04-25 14:26:46.97