SSTC Blowing Mosfets

Zach240sx, Tue May 23 2017, 08:34AM

Hey there,

So this is my first post, HEEELLLLOOOO!!!!

I will get more in depth on this tomorrow when I have more time to wright. I have a full bridge setup I just made, I have ran it on a couple small power supplies. 20v 90W laptop charger, 28v 2a transformer. It works quite well. Now I don't have a variac to step up mains slowly(USA 120vac). What I came up with was a CFL LED 150watt dimmer. I first just tested its output voltage after rectifying and using a light bulb for load. I got it down to 18v Sweet!!! So I went ahead and tested it. First try, I got light up right away . Of course me being to excited I started to turn it up and up. Totally spaced I had a 120watt halogen for load...oops... I meant to lower the crap out of that once I established my first light. So It fried the dimmer along with two Mosfets(1 High and low side)...

Well I fixed that, So second try... I get it to light up but only for 5-6 seconds and it dies, dimmer starts to hum. I Look all through my circuit and realized when I changed my lower current fast switching diodes for higher current ones I plugged one of the diodes and drain output one bread board pin off(I did this before the first test) So My first light was on a screwed up half bridge. Plugged that in correctly, replaced the Mosfets on the other sides high and low side. So third try, This time still with 120w bulb just to start, I turn it on and wow way better then the first light, probably 4 inch streamers with dimmer all the way down.(Full bridge definitely working now) I shut it off and try a forth time, Lights up again... Sweet!!! so before anything else happens i turn it off grab my phone for video, set it up, turn it on ....nothing, I also hear a hum. Its the dimmer, popped a high and low side Fet again!!!!

So the dimmer fried most likely do to the 120watt halogen, wile trying to up the current. the fets must be getting a surge when I power off. Can someone help me with this. I drew a quick diagram of my half bridge. Could this be a voltage spike causing gates to pop over 20v? do I need zeners? i have a bunch of 15v. The dimmer is just in between the mains and rectifier.

Thanks guys