I must have missed something. What happens when you put a spark plug across the secondary? Is there ever a need to short the secondary? I would also like to build a spark generator for a model engine. John Ferrell 6241 Phillippi Rd Julian NC 27283 Phone: (336)685-9606 johnferrell@earthlink.net Dixie Competition Products NSRCA 479 AMA 4190 W8CCW "My Competition is Not My Enemy" ----- Original Message ----- From: "Jay Shroff" To: Sent: Friday, October 03, 2003 7:38 AM Subject: [PIC]:High Voltage problems help - Additional info and observations Couple of points Thanks to everyone for the suggestions, you know it is amazing how much information you end up leaving out when you post for help and I apologize for 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 out of laziness, in hindsight I should have left them in so as to avoid any confusion. 2. To the end use - I am developing an electronic ignition for a 32 cc ryobi gas engine to use in a RC plane and though such ignition modules are commercially 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 obsessed since it does not work!!)... I have not designed the final stage - dumper capacitor, scr triggering etc. I figur ed I would get 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 and then hook up a bridge rectifier to the secondary feed it to a dumper cap 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 pic 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 mentioned that just eliminated the flyback action and the voltage on the secondary 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 pins and noticed that every time I shorted the secodary I was getting a huge spike across the scope, well decided to add a 5.1V zener between ground and the PIC's VDD, what do you know the pic no longer locks up on shorting the secondary... I still get the LED to light sometimes when shorting - I suspect that's becuse the voltage spike is running accross the unprotected 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 some light. based on the input I recieved so far I theorize that shorting the secondary was causing massive coupling into the primary along with the 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 fix 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 capacitive 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 -- http://www.piclist.com hint: PICList Posts must start with ONE topic: [PIC]:,[SX]:,[AVR]: ->uP ONLY! [EE]:,[OT]: ->Other [BUY]:,[AD]: ->Ads