LED driver and auto power off circuit

[Rocket-Man66666]

Heey guys, here I am again with yet another question. Got such great help last time, figured this would be the smartest thing to do.

I have a small circuit to drive some leds with a audio signal. Works like a charm.

Now I have the tendency to forget to turn the sucker off every now and again...
How bad is this on the battery and would it be usefull to use a circuit to conserve power?

 

[MikeMl]

Replace the battery with a 9V wall-wart.

 

[Rocket-Man66666]

Not really the most useful answer and not possible either.

 

[ChrisP58]

Not really the most useful answer and not possible either.

Then perhaps you can be a bit more clear about what you are looking for.

What condition do you want to drive the auto power off function?
- Time?
- Absence of input signal?
- ?

 

[Rocket-Man66666]

I know off a simple circuit which uses a FET to time the thing and then turn it off. However, it uses a momentary switch and this means I can't turn the led driver off before the timer shuts it down and it would be nice if the timing part would only kick in after there hasn't been an audio signal.

I'm terms of timing: it doesn't have to be precise to the minute and I am talking about a shut down after about 10, 20 minutes. And the smaller the the circuit, the better.

 

[ChrisP58]

What op-amp are you using? As I look at the circuit, the LEDs should be totally off when there is no audio, so only the op-amp would be drawing power.

The simplest thing would be to just change the op-amp to a single supply part with a very low quiescent current, and leave it on all of the time.

 

[Rocket-Man66666]

Yes that is correct. I'm using a LM358N.

 

[ChrisP58]

The LM358 has a typical quiescent current of about 1 mA per amplifier. And, even though you are only using one of the two amplifiers, they are both drawing current, so your op-amp is consuming 2mA. That is about 5% of your load current, so that is considerable.

Look for a single op-amp with Quiescent current under a microAmp. Off hand, I don't have any part suggestions though.