Re: SSTC-556 timer IC malfunction

["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 1/14/02 6:48:00 PM Eastern Standard Time, tesla-at-pupman-dot-com 
writes:

<< Your problem with the 555 and driver circuit is a combination of not
 enough current supply, and not having transistors that can handle the
 current.  Your power supply should be able to supply at least 5 amps,
 I would say 10.  Ignition coils can suck up a lot of current.  If you
 don't have a large enough power supply, you could use a car battery,
 or get a gel-cel from a hobby store.  Your output transistors also
 need to be able to handle a large current, and be able to dissipate a
 decent amount of power.  The FET will help, but don't be surprised if
 it blows out - I'm surprised that the transistors you have right now
 are still alive.  You could get a decent powered FET from Raido Shack,
 or order one from a supplier like Maxim.  If you use a FET, it won't
 have to dissipate much power, so a large heat sink wont be necesary. 
 Just get an N-channel, enhancement mode FET, with a continuous current
 rating of at _least_ 5 amps, I would say 10 A.  However, FETs are very
 sensitive to static electricity, and high voltages.  BJTs are more
 robust.  I would use a 2n3055, which is an NPN type.  It will handle
 15 Amps continuous, but will dissipate more power than the FET, it
 will need a heat sink.  If you would like a schematic to hook any of
 this up, let me know, I will be happy to provide one for you.
 -Sean Taylor >>

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"?

Matt