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Old 25th Oct 2018, 6:56 pm   #24
Trigon.
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Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 382
Default Re: Retired Texas TI99/4A engineer needs help please.

Quote:
Originally Posted by Boater Sam View Post
is the UA724CNG4 the same chip or the UA724CN?
G4 is just one of the 'eco' suffices - basically means lead-free.
Quote:
Originally Posted by Boater Sam View Post
I have no knowledge of how TL331 works, I thought it was a comparator. You say it should be generating an oscillating output? Presumably this is in the 20kc/s range to run the switch mode regulator chip?
It is. It alternately charges/discharges C16, comparing the voltage with the reference set by R11, R15-20 and the positive feedback via R13 which creates the hysteresis defining the amplitude. The waveform is asymmetrical because the output is open collector, so it discharges via R14 but charges via R14+R12.
Quote:
Originally Posted by Boater Sam View Post
Prices for these are crazy, is there a good reason?
It's probably been obsolete for a very, very long time.

Cheers
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