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Old 29th Jul 2018, 8:00 pm   #13
Noopy2014
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Join Date: May 2014
Location: Eichstätt, Germany
Posts: 88
Default Re: Gould 4072 bad PSU

In my understanding it works like this: High-Level on Pin 10 disables the 3524.

There are two causes that disable the chip:

1. If the input-voltage (PLD 7,8) is to low for a proper 12V-supply the zener D15 doesn´t conduct, than there is low on Q12 base, than there is high on D16, an the 3524 is of cause of low supply.

2. For the second cause you have to realize that the upper switching supply works with the input voltage minus the voltage of the lower switching supply. That means that a too low voltage on the output of the lower supply gives a too high voltage on the upper supply.
The second path around Q10 switches the 3542 off whenever the voltage on the output get´s too low. With switched off lower supply there will be no voltage on the upper supply because the power fet Q14 is (hopefully) off.

Sorry for my English. I´m in a hurry...

Best regards, Richard
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