Re: SSTC-556 timer IC malfunction

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

Original poster: "Sean Taylor by way of Terry Fritz <twftesla-at-qwest-dot-net>" <taylorss-at-rose-hulman.edu>

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

-------------------
> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Fucian-at-aol-dot-com>
> 
> Hi, i just recently used a staccato design with the 556CMOS IC.I was
doing 
> pretty good for being me.Once i added a MOV across the primary, the
staccato 
> just failed immediatley.WHY?The funny thing is that it still is
pulsing.At 
> the wrong frequency of coarse but it wont respond to POT
adjustment.It seems 
> to be locked or something.I get no ouput from the SSTC.Not even a
sizzle.I do 
> get a sizzle out of an ignition coil.What could be happening?Also
everytime i 
> try using a totem pole transistor arangement with a 2N3904 and
2N3906, the 
> output voltage drops to about 7volts.WHY?My power in to the 556 and
the 
> transistors is a 12 volt 400ma adapter.Ive tried using a 18volt
1.6Amp 
> adapter as well.The more powerful one only raises voltage to 8volts.
I dont 
> want to stress the 556 by ussing it to directly drive the MOSFET so
I have 
> decided to order a MOSFET driver from MAXIM.Is anyone had any
experience from 
> them?It can handle 2A continuous.
> 
> Matt
> 
> 
> 
>