Re: SSTC-556 timer IC malfunction

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

Original poster: "Jan Florian Wagner by way of Terry Fritz <twftesla-at-qwest-dot-net>" <jwagner-at-cc.hut.fi>


> The 556 CMOS draws very little current.So does the transistors.I think you 
> got me mixed up here.I have a seperate supply for the coil.The transistor 
> pair is there to deliver more current to the FET gate.I have a totally 
> seperate supply to power the coil and MOSFET. I have had NO timer probs 
> before.It just all of a sudden happened.Is it possible for a timer chip to 
> "Lock up"?

Did you already try "shielding" the 555 timer and gate drive part of your
circuit from the rest of the stuff? Like wrap a bit of tape and
after that aluminium foil around the 12V side component board?

Some sort of HV coupling back to the 12V side is the main thing that comes
to my mind when you said your 556 circuit "locks up". CMOS is probably
especially sensitive to this HV back coupling, so shielding is important.
A TTL 556 might run "better" in this case (without shielding), but then,
TTL has other drawbacks...

cheers,
 - Jan

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