On Thu, Feb 7, 2013, at 10:37 PM, Josh Koffman wrote:

> Just so I'm clear, is the basic aversion to buck-boost that it's
> comparatively inefficient and just not a great solution? I'm certainly
> not against running off of 3 cells, so that no matter what I will
> always be below 5V input.

Yes, depending on the topology it can be less efficient, more
complicated, or the noise spectrum is going to be wider because of the
transition. And since you get to choose the input voltage, you can avoid
sub-optimal designs.

> > In your project, is it possible to use two or three cells, power the
> > amplifiers directly off the batteries, and use a step-up for stuff that
> > absolutely needs a regulated voltage?
>=20
> I think so. My concerns with powering the headphone amp off the
> unregulated supply are that as the batteries droop I will start to
> lose volume (not a huge problem), and that while I don't know if the
> PSoC analog section will put out a rail to rail signal, I don't know
> what will happen if I feed the amp with a signal that is greater than
> its Vdd.

Since your amp is not running a gain of 1, you won't ever be in the
situation of driving it with more signal than the supply rails. And the
gain doesn't change with supply voltage, so the volume won't change.
Your maximum undistorted volume will be reduced as the supply voltage
goes down, that's all.

I don't think I'm wrong to say every mp3 player currently in production
runs the headphone amp straight off the battery. Lots of reasons, but
basically the voltage regulator can be a lot smaller and you don't have
the losses.


Cheerful regards,

Bob

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