UPS Circuit Protector

Hi there guys!

I would like to design a circuit to protect a UPS from a fast transient peak of current, running at 120v. I would like to clamp or suppress this peak so the fuses and transistors on the power supply don't blow up.

I would have a maximum current from 1 to 2 amps max.

Any circuits or theory to help me would be appreciated.

the "old school" method would be to put a ballast resistor (usually an appropriate sized incandescent light bulb) in series with the load. for 1 or 2 amps this would be a 150 or 200W bulb. while cold, the resistance is small and so very little voltage is dropped across it. with current transients, the filament heats up, and it's resistance increases, dropping more voltage and limiting the current in the load. i use this method for initial testing of amplifiers and A/V receivers after i repair the amp or power supply section.

I want to make a circuit to avoid the peak current to the UPS because it is not capable of supply it quickly and the fuses blow. I have found that with passive element RLC this can be done but had found no equations to know what values to implement.

PD. I am talking of AC current. That is why it is a little more challenging.

You could use an NTC thermistor in series with the load to suppress a power-up transient.

Otherwise known as a positor, you can still get them as spare parts for tv's