[sdiy] Shutdown on chip-amp

[Roy J. Tellason]

On Monday 02 May 2005 02:00 pm, Neil Johnson wrote:
> Hi,
>
> Big N-channel MOSFET (with low rDSon) in the GND line of the power amp
> circuit.  Drive the gate with a logic signal from the PIC.

Don't even need a big one or that low a resistance with that little bit of a 
load.  Radio shack used to sell the VN10KM,  which came in a package that was 
a variant on a TO92,  and that should do the job...

> Hope this helps,
> Neil
>
> On Monday, May 2, 2005, at 06:45  pm, Johannes Öberg wrote:
> > Short version: I need to make a small mono power amplifier (probably a
> > LM386) shut down into some sort of low-power mode when not used, and
> > this will be controlled by a PIC. I'm a total newbie.
> >
> > Longer:
> >
> > I'm building a small batteryoperated door-bell out of an ISD2560
> > (lofi-sampler-on-a-chip) and a PIC. I guess I could have saved on
> > parts, but it's my own "design" so it's a bit of an overkill to get it
> > working.
> >
> > Anyway, I'm trying to reduce the power consumption as much as
> > possible. I'm using the PIC in shutdown mode with interrupt-on-change
> > so it only draws power when you press the door bell button. The ISD
> > has a built-in power saving mode.
> >
> > All this works so far.
> >
> > However, while the ISD can drive a speaker directly, it is way too
> > quiet for my needs. Therefor I need to use an external amplifier. The
> > only one with built-in power down mode I can find readily available is
> > surface mount :-(
> >
> > I looked at the LM386, but how do I make it power down? Can I just put
> > some kind of PIC operated switch on the voltage supply for the LM386?
> > Which one would you recommend? It doesn't matter if it's expensive
> > because this is going to be one-time quick-and-dirty fix.
> >
> > Also, unfortunately, I'm short on time, and only have access to parts
> > from www.elfa.se (the only local electronics supply), aparts from the
> > random stuff I have at home of course.
> >
> > BTW, the LM386 only gives out 325 mW. Is that enough? I have little
> > idea about these things, I have a 1W radio somewhere that is awfully
> > loud even at low pot settings, so that's why I figure 325mW would be
> > enough. Am I way off?
> >
> > Thanks in advance.
>
> --
> Neil Johnson <http://www.njohnson.co.uk>