I am trying to choose a good (as in proper values) PTC for my USB power supply project for micro-controller. I am looking to make a simple power supply for breadboarding purposes. The little gadget will provide USB 5V at 500mA or 3.3V/3.6V at 300mA via an LDO. So, my questions are:
From DigiKey's list of thousands of avail PTCs ( http://search.digikey.com/script... ), I am a bit confused of the right values to choose for time to trip, current trip, and current hold.
I would choose 10V as the max. voltage for both the 500mA and 300mA case, since the max voltage is 5V. So, that should be safe enough
1. For the current trip value, should I go about 5% less than the max current output? That is, for example, for the 500mA max output at 5V, is 475mA a good value? Or ok to have 500mA and still safe?
2. current hold. 5% less than the max current output? A good figure?
3. Time to trip. What would be a good value?