Re: SSTC 555 timer problem

["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>

Matt,
What output is only at 6.5 volts?  if you have a 50 % duty cycle going from
0 to 12 V, then you will have an output from the 555 of about 6 volts
according to a DMM.  If you look at it with a scope, you should see the 0
and 12 volt levels alternating back and forth.

Different FETs have different turn on levels - some are designed for TTL
level (5 V), some are higher, some are lower.  You have to look at the
datasheet.  Generally, they are higher then 5 V though.  BUT, you have a 12
volt pulse that is turning the FET on, then a 0 V pulse which turns the FET
off . . . exactly what you want.

It is possible to replace the FETs with IGBTs, but you have to get one that
operates at a high enough frequency.  Depending on the size of your coil,
that might be hard to find . . .

Sean

----- Original Message -----
From: "Tesla list" <tesla-at-pupman-dot-com>
To: <tesla-at-pupman-dot-com>
Sent: Saturday, August 24, 2002 1:13 PM
Subject: SSTC 555 timer problem


> Original poster: "by way of Terry Fritz <twftesla-at-qwest-dot-net>"
<Fucian-at-aol-dot-com>
>
> Hi yall i have a question.
>
> I am using a 555 time rin 50% duty sycle mode for a small SSTC.It is using
a
> 12volt regulated supply and is only outputing about 6.5 volts.Nothing gets
> got, not even the totem pole transistors.Do yall get this same
output?Whats
> goin gon here?With the normal 555 astab;e mode with variable duty cycle, i
> get around 10 volts out.Whats up with this 6 volts crap?
>
> Dont MOSFETs need at least like 7-8 volts to even turn on?Is it possible
to
> replace MOSFETs with beefy IGBTs?
>
> Matt
>
>
>
>