Couple of points=20 Thanks to everyone for the suggestions, you know it is amazing how much inf= ormation you end up leaving out when you post for help and I apologize fo= r not being more detailed. To fill in the details... 1. Like Bob Blick mentioned I did have current limiting resistors going to = the base of TIP42C and to the anode of the LED I just did not show them o= ut of laziness, in hindsight I should have left them in so as to avoid an= y confusion. 2. To the end use - I am developing an electronic ignition for a 32 cc ryob= i gas engine to use in a RC plane and though such ignition modules are co= mmercially available I decided that it would be a fun exercise to design = this on my own. ( I should have stayed away from it as now I am totally o= bsessed since it does not work!!)... I have not designed the final stage= - dumper capaci=D4tor,=D4 scr triggering etc. I=D4 figur=D4ed I would ge= t the HV stage working and then the rest would be simple, plus I assumed = that with the PIC PWM the HV stage would be a piece of cake, well Murphy = struck again. so the plan was to drive the transformer in flyback mode an= d then hook up a bridge rectifier to the secondary feed it to a dumper ca= p and trigger it via an SCR. 3. Results so far based on everyones suggestions A. Tried Olin's Diode idea - I understand the logic there and should have = had it from the beginning but unfortunately after adding the diode the pi= c still froze when I shorted the transformer secondary for a second, even= when undoing the short the pic would not recover. B. I had tried a diode across the transformer primary but like Russell ment= ioned that just eliminated the flyback action and the voltage on the seco= ndary dropped to about 25 V. (but the pic did not lock up :-) C. I tried the snubber capacitor across the transistor output, but maybe I = need a fast diode for it to work correctly because it still locked up the= pic. D. I had a logic level mosfet IRLZ44N so I tried that also, with the diode = across source and +5 V etc but still same lockup. E. Cursed at the circuit a bit and then hooked up the scope to the supply p= ins and noticed that every time I shorted the secodary I was getting a hu= ge spike across the scope, well decided to add a 5.1V zener between groun= d and the PIC's VDD, what do you know the pic no longer locks up on short= ing the secondary... I still get the LED to light sometimes when shorting= - I suspect that's becuse the voltage spike is running accross the unpro= tected led?? I will try adding a zener there also. I guess I might have fixed the symptom but am still a bit puzzled about the= cause and am hoping that the collective wisdom of the piclist can shed s= ome light. based on the input I recieved so far I theorize that shorting = the secondary was causing massive coupling into the primary along with th= e continuing pwm action on primary was feeding a current through the VSS,= VDD pins to the unprotected PIC, is that correct? Also as someone mentioned a snubber capacitor should be the right way to fi= x this right? What would a good configuration be?? so that I do not have = to throw zeners on all points that I connect tothe supply :-) BTW - One additional reference point - I isolated the PWM pin and drove the= primary through a 555 oscillator (still using common ground) and I still= managed to get the pic locked up, so I am guessing that the spike that I= observed around the supply was really the main culprit. Thanks for all the input so far, I would'nt have made it so far without the= extremely helpful hints from everyone. Jay -----Original Message----- From: Russell McMahon To: PICLIST@MITVMA.MIT.EDU Date: Fri, 3 Oct 2003 16:33:09 +1200 Subject: Re: [PIC]:High Voltage problems help > I don't remember hearing an explanation of what the output of the > transformer was used for. You're correct (of course :-) ). I was inferring more than he explicitly said, and possibly wrongly. He noted a 5v supply, 30:1 transformer ratio and 200 volt out on no load. I ASSUMED therefore that he was using it in flyback mode. I assumed the O/C voltage limitation was caused by stray or other capacitiv= e storage. We need more information on what is required to be done. Russell McMahon -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu -- http://www.piclist.com hint: To leave the PICList mailto:piclist-unsubscribe-request@mitvma.mit.edu