Electronics > Projects, Designs, and Technical Stuff

Auto-Standby circuit doesnt work as expected

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Michaelaudio:
I know I know. But I already have the pcb and its working fine except for this problem, so I dont wanna make a new board and new schematic, i wanna fix the actual problem (spent way too many hours on this project to give up)

tooki:

--- Quote from: Renate on August 06, 2020, 08:15:26 pm ---I'm late to the party, but 2 M ohm and an electrolytic?
You like living dangerously.
A long analog RC delay is so Flintstones.

Even back in the day, they would use an RC oscillator and count 16384 or more pulses for long delays.


--- Quote from: Ian.M on August 03, 2020, 07:09:00 am ---The whole approach of an extremely large time constant RC network with an electrolytic cap is irretrievably flawed
--- End quote ---

A quick glance at the TPA3116 shows that there is no disable pin (or did I miss some multi-pin usage?)
Use a chip that has both mute and disable.
Intercepting power to the chip is a poor approach.

--- End quote ---
You missed it. There’s a mute pin and a shutdown (SDZ) pin. One of the op-amps in the full schematic (which he inexplicably refuses to post in this thread, despite posting it in another thread already) is part of another circuit (drawing power from an internal power rail despite the datasheet explicitly saying not to do this) to control the mute pin.

Renate:

--- Quote from: tooki on August 06, 2020, 11:28:35 pm ---You missed it.
--- End quote ---
I did!
If you look at the block diagram (which is what I did) the innocuous "SDZ" in the upper left corner doesn't really seem to go anywhere.

Unrelated: Looking back at my notes, my guitar amp uses a TDA7296, 60 W, class AB.
Interestingly it uses max 65 mA quiescent current, compared to the TDA3116 at 50 mA (which is class D).

Michaelaudio:
@tooki  i wouldnt do it again  but the cap on gvdd is charged with 70uA for like 3sec. So shouldnt be a problem. Everything works just fine except for the problem im trying to get help with.

Renate:
Why don't you remove the big P MOSFET, bypass it, invert the sense of your gate drive circuit and make it an open collector into the FAULTZ & SDZ junction.

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