Re: FBSSTC-NEED HELP

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

Original poster: Jan Wagner <jwagner-at-cc.hut.fi> 


On Tue, 23 Mar 2004, Tesla list wrote:
 > Hey sorry for the lack of response on the last post..-dot-computer crapped
 > up...Im actually usuing a 1084...and its doing fine...Thas the
 > bewilderment...I get 12 volts out...I traced the voltage into the 555...got
 > 12 volts out of pin 3 but no DETECTABLE frequncy...sometimes 60hz but my
 > DMM seems to say 60hz even when not connected :-P

And if you disconnect the 555 output pin from the 4420?
What freq do you get on the 555 timing R or C?

 > Anyways, i then trace the voltage to the 4420...its there...but nothing
 > out...WEIRD ISNT IT? a 555 that has 12 volts out...and seemingly no
 > signal?And then a 4420 that...does...nothing....

You probably already checked that the 4420 _really_ does get 12V to both
supply pins? I.e. pins 1 and 8? And both ground pins properly connected to
ground? If the 4420 (=non-inverting) still doesn't put out 12V with a
logic-HI input signal on pin 2, then its fried.

If you were driving a gate coupling transformer, and you didn't have
schottky diodes on the 4420 output pin to ground pin and +12V pin, then
the reverse inductive current may have fried the 4420. The datasheet says
"virtually latch-up proof". Yeah. Virtually. In reality though, if your
unlucky with the gate drive transformer design then the 4420 may actually
fry (I've been quite successful at it ;-)

cheers,
  - Jan

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  Helsinki University of Technology
  Dept. of Electrical and Communications Engineering
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