>>Still looking  for that ideal IC alas :-)

> I don't gave up easily. It's not an ideal IC but is a $0.4 design 
> per
> one piece (connecetors was not counted):
>
> 2x LM386 + 4 diode + 2 resistors (maibe 2 capacitors).
> I know you can figure the schematic. So tell me about this 
> suggestion.

I like the LM386 and have used it in various tasks.
The bad news is that it falls down in too many areas in this 
application.

The good news is that that's seriously good lateral thinking - there 
may yet be something out there that does do the job.
Using what is essentially a power opamp is promising.

Now for why it, sadly, doesn't do the job.

- They don't intend it for such substantial current levels and it has 
high saturation voltages at higher currents. Even at no load it has 
poorish saturation voltage as this is not important in its intended 
role as an audio amplifier. eg

        http://www.national.com/ds/LM/LM386.pdf

With Vsupply = 6v and NO load Vp-p out = about 5V. 1V lost. At 4 ohm 
load (remembering that this is 4R relative to centre voltage so it 
sees half the available voltage, Vpp out = under 3 volts. I effective 
= 3/2/4 = 375 mA peak. At 8 ohm load = 180 mA ish peak it's 4v out or 
2v lost. That's about the same as the existing bridge and far worse 
than I want to achieve.

- No load quiescent current is about 4 mA or 8 mA for two. That's 
about 1,000 times what I want, I could add a series on/off transistor 
but that adds complexity and extra drop.

- Minimum Vsupply = 4 volts which is OK but less would be nice in 
practice and a transistor bridge has no lower limit - it just keeps 
getting gradually worse .

- No voltage limit for load but this could be easily added with a 
zener and a few R's per side. Increases IC dissipation which may be a 
problem.

- No electronic brake, but that can be separate.


Keep them cards and letters coming. Somewhere out there is the ideal 
IC. I hope :-)


        RM




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