Electronics > Projects, Designs, and Technical Stuff
Auto-Standby circuit doesnt work as expected
Michaelaudio:
Correct. And i did put the Symbol on the drain of Q4 so I dont know what Ian.M means, the Timing circuit is always powered ofc.
Ian.M:
--- Quote from: Michaelaudio on August 03, 2020, 09:14:53 am ---Oh my fault! I forgot to switch the Power Symbol, the circuit is always powered ofc.
--- End quote ---
--- Quote from: tooki on August 03, 2020, 09:27:27 am ---VDD is the unswitched always-on power, and VCC is the switched power, correct?
(And no, I don’t know why it’s not working, sorry! But I’d listen to Ian.M.)
--- End quote ---
--- Quote from: Michaelaudio on August 03, 2020, 09:39:28 am ---Correct. And i did put the Symbol on the drain of Q4 so I dont know what Ian.M means, the Timing circuit is always powered ofc.
--- End quote ---
That's not what your schematic shows. If VDD was always on, the IFR5505 P-MOSFET would be ineffective for switching VCC as its body diode would conduct when there was no gate drive.
Ergo you haven't built it as drawn, don't understand it and our attempts to help you are as futile as pissing up a rope.
As a reminder and to prevent O.P. being tempted towards revisionism, here's the relevant section of the schematic (annotated with my understanding of its connections). The only other points worthy of note is that the rail splitter providing GNDA is also fed from VDD.
tooki:
As I gather from the full schematic from his other thread, Con7 is where the 24V is fed into the circuit, so it’s definitely not switched. But yes, you’re right, the way that mosfet is used, it won’t ever turn off VCC!
Michaelaudio:
Okay yep! Q4 is wrong on the schematic.. S and D need to be switched, so on the pcb the Mosfet is connected right (S to power supply D to the Diodes) guess I should update it and post the right schematic.
Michaelaudio:
Okay so I figured out, that the voltage drop after the voltage goes above 7.7V on Pin 5 is the Voltage of the hysteresis. If I replace R76 with a 100K the voltage drop is 1.2V with 1M its 0.1 so its obviously the hysteresis voltage.
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