TL494 SMPS help required

[Martin Whybrow]

I'm fault finding a PSU (an argon ion laser PSU) based around a TL494 SMPS
controller. The SMPS is arranged as a single ended series regulator with
both drive outputs of the 494 in parallel driving the switching FETs. The
dead time control pin (pin 4) is at 0V, but the drive output at pins 9 and
10 is showing 100% duty cycle, the data sheet states it should have a 5%
dead time. The oscillator is running, I get a 100KHz sawtooth at pin 5 (Ct)
ramping from 0.4V to 2.6V and the Vref (pin 14) is correct at 4.99V.
Is the TL494 dead? Any other ideas.
TIA,
Martin.

 

[Michael A. Terrell]

I'm fault finding a PSU (an argon ion laser PSU) based around a TL494 SMPS
controller. The SMPS is arranged as a single ended series regulator with
both drive outputs of the 494 in parallel driving the switching FETs. The
dead time control pin (pin 4) is at 0V, but the drive output at pins 9 and
10 is showing 100% duty cycle, the data sheet states it should have a 5%
dead time. The oscillator is running, I get a 100KHz sawtooth at pin 5 (Ct)
ramping from 0.4V to 2.6V and the Vref (pin 14) is correct at 4.99V.
Is the TL494 dead? Any other ideas.
TIA,
Martin.

Try --
We now return you to our normally scheduled programming.

Take a look at this little cutie! ;-)
http://home.earthlink.net/~mike.terrell/photos.html

Michael A. Terrell
Central Florida

 

[als]

If you are seeing an output, chances are the chip is fine.
They seem to be tough little critters. If the output pins
are paralleled, chances are that what you see is the overlap
and/or circuit hold-up. There are some example circuits at:
http://people.txucom.net/andysm/pages/drawing3.html
that you may find handy; if not, contact me on:
http://pub99.ezboard.com/bdefcon9
I have started to use these things instead of a 555.
<als>