Re: SSTC probs

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>" <Fucian-at-aol-dot-com>

In a message dated 11/28/01 10:19:34 AM Eastern Standard Time, 
tesla-at-pupman-dot-com writes:

<< >I tried a higher voltage supply to power the 555 and it SEEMS to help.I 
did
 
 Whoa - don't use a 555 to drive the gate!!! Get yourself a nice $5 chip to 
 do it - those babies kick butt and are worth every cent you spend on them 
 =) So protect them with filtering caps and maybe a zener and they'll make 
 your setup purr like a.. err.. coil? =)
 
 >get twice the output but that quickly left.I was back at normal output with
 >occasional better output.
 
 Sounds like it was getting pretty hot or dying in some other way..
 
 >I think that the MOSFET is taking too much CEMF.How
 
 CEMF?
 
 >
 >can I block it completely?My circuit is just a plain simple 555 pulsinga
 >MOSFET.The MOSFEt is directly driving the primary.
 
 Like I said, use at least a half bridge, otherwise you're gonna kill the 
 MOSFET with flyback pulses, or heat the clamp diode if it's fast enough to 
 catch them.. Or do both which is more likely =)
 
 There's lots of circuits on the Web.. look for one which has been tested 
 and put in the effort to build that. There's no fun in frying MOSFETs, it's 
 like crashing model aircraft because you used really old batteries for the 
 radio... Just more trouble than it's worth and it makes you put it away 
 after a while =( So do read books, do try a 12 V version until you think 
 it's perfect, and do bother with all of those protection diodes and ringing 
 suppression resistors =) It takes longer to mount another 10 MOSFETs in the 
 end =)
 
 >Matt
 
 Darren
 
  >>
Ok, well I dont have the time or the money to make those complicated 
circuits.It seems the that with every new design comes a new thing that is 
really a bother to find.(Gate drive transformers?)

Im getting pretty overwhelmed with it all.(Highschool senior).
I thought i saw something about a 556 using 1 timer to pulse the other?How 
well does this work?A circuit based on that seems easy.And what the heck are 
all these gate drive chips for? :-? Could I get away with something like a 
2n2222 to pulse the MOSFET?Another 14 pin driver just adds to the 
complexity.I have seen stuff about half bridges.Those sound easy enough but 
the circuits i see only confuse me.They are broken up into parts with jumper 
wires going here and there and Im not sure whats going on.

So, im looking at either a 556 based or a Half-bridge.Does anyone have a 
schematic I can see that is easy to follow of one?Are transformers really 
neccesary?Cant diodes block the stupid CEMF?How well would a 556 do?Im sure I 
could figure out a circuit for it.Just what kind of timing should I use for 
pulsing the second timer?

Im sorry that I sound to be harping and moaning and I guess I could be over 
my head.Ive just got so much going on and have killed about 20 MOSFETs and am 
really frustrated.I really HATE the current 555 timer pusing a MOSFET cuz I 
hear of all these problems that could have been my reason for frustration.And 
im stuck with stupid Radio Shack proto boards that leave me with wires going 
everywhere and look very crappy.The tuning seems to be one extremely 
SENSITIVE spot on the pot.

Grrrrrr........
Matt Gibson