Electronics > Projects, Designs, and Technical Stuff
Auto-Standby circuit doesnt work as expected
Michaelaudio:
So I found out that when I short R69 the Voltage on Pin 5 ic9 goes back to zero when its been over7.7V , so Q2 fully closed then. Same thing when I remove R70. When I remove R69 and look at Pin 1 ic9 with the scope when Pin 7 gets a high, Pin 1 is also getting also high for also short time(its pulsing a little bit)
Michaelaudio:
So it seems no one can help my but anyway, when I remove R64 and R65 it works. Now I havent any more ideas (C1 and c15 arent the problem either)
Ian.M:
Am I correct that R64, R65 carry the signals going to the activity detector circuit round IC9A?
If so, it would seem that cutting power to VCC causes a glitch affecting those signals, which causes a false activity detection so turns the power back on.
You need to modify it to either lock out the activity detector for a few seconds after the timer cuts power, or to slow down the speed with which Q2 can reset the timer so it needs sustained activity, not just a btief glitch. Inserting a resistor in series with Q2 collector may do the job - I'd start by trying 1K.
Michaelaudio:
Yep.
It actually doesnt turn off at all, the voltage of Pin 7 IC9 switsches so quickly that it doesnt turn off Q4. Looked at VCC while Pin 7 is pulsing - nothing to see, looked at the inputs (r64/R65 going straight to the RCA connector) same thing - nothing. And I dont see why a 1k to the collector would change something, there is already a 2M in series isnt it?
Renate:
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.
(I just retrofitted my guitar amp. It has both mute and disable. I have an ATTiny85 running power sequencing.)
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