Electronics > Projects, Designs, and Technical Stuff

Auto-Standby circuit doesnt work as expected

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Ian.M:
What's the state of the pin 7 output after you observe this voltage drop?  If the OPAMP is correctly wired as a comparator with hysteresis, you should get a step change of the pin 5 voltage upwards, as the rising input voltage crosses the reference level on pin 6.

Michaelaudio:
So the Voltage at Pin 6 is 7.7V when the voltage at Pin5 is at lets say 7.71 Pin 7 is at ~23V (the LED blinks for like half a sec) after that the output is ~0.7V and the voltage on Pin 5 is 7.6V. When i take R78 out (Gate resistor) The voltage rises just fine and the output is constant. I tried a higher value for R78 but changed nothing. Really weird..

Ian.M:
What happens if you disconnect R69 (base drive to the timing reset transistor Q2)?

Where is IC9 getting its supply from?

Michaelaudio:
Havent tried that yet.
Thats getting the Power from VDD (directly from power supply)

Michaelaudio:
Okay verry interesting things going on here. When I disconnect R69 while circuit powered up, Q4 opens! When I then connect it again, Q4 is closing (low on Pin 7 IC9b). When I turn psu off, wait 10 seconds (resistor disconnected) turn it on again Q4 still open. Verry interesting
Btw I replaced R71 with a 100K to Charge te cap faster, shouldnt be a matter

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