130Views7Replies

# SMPS formulas? Answered

are there any switched mode power supply formulas? I've been googling but I can't find anything... I need to know relation between duty cycle (I'm using square waves) frequency size (value) of the inductor output voltage output amperage how many amps should the inductor be rated for (is it how much your drawing?)

Tags:

## Discussions

you know, i skimmed over that instructable earlier and didn't find it useful, now that I read it in depth i found it incredibly useful. One last question. Is there a limit to how much the voltage can be boost, or does it approach infinity as current approaches zero?

I think in theory you can go as high as you want, and in practice things like resistance, edge sharpness, transistor breakdown voltage, and so on get in the way. I have successfully taken a "white LED from 1 AA battery" circuit swapped in HV transistors, and used it to drive a neon bulb, and EL driver circuits for "indiglo" watches don't seem to have any trouble getting 80+V out of a 3V battery...

oh, and while you're here, is it better to have high inductace or low inductace? I'm trying to boost 120 VDC (rectified mains) to 6KVDC (I was originally going to say 8, but 8kv diodes are cheap and easier to find then a higher voltage). Would you say about 100uH is fine? According to my calculations (felt really nerdy there, hah) if I use a 100uH inductor driving it with 120 volts at 1.7 amps (I'd use a 2.2 amp inductor) I"d get an output of 6kv at 12.75mA (about 100 watts of power!). Coming to think of it I think this might be a bit over kill cause I'm trying to build a really tiny fully contained tesla coil, and 100 watts of power in such a little device...

Uh, do you have a 6kV switching transistor? SMPS make my brain hurt, but as far as I can tell, inductance has more to do with frequency of operation than overall efficiency. Lower inductances require higher frequencies, and higher frequencies permit lower inductances... The sort of generic boost converter I referred you to tends not to be used for very high voltage supplies; it's just much easier to put a second winding on your transformer and get part of your boost from the turns ratio.

wait, doesn't the transistor just have to be able to handle the input voltage?