DC voltage multiplier for batter powered amp

[scwhiteley]

I'm working on a portable amp project and am wondering about the feasibility of using a dc voltage multiplier so that I might reduce the size (and cost) of the battery pack.

The most recent amp I've built is a class D unit using the TPA3110D2 from TI. On other portable stereo applications, I've used pretty large battery packs (i.e. 12 NiMH cells to generate 14.4v) But for this next project I'd like to go a bit smaller.

The TPA3110D2 can be powered by as little as 8V (and as much as 26V).

What I'd like to try would be a 3 cell (3.6V) or 4 cell (4.8V) pack, so that the battery could be recharged from a USB port.

The problem here is getting the voltage up to the minimum 8 volts required by the amp chip. Also, if I recall correctly, the chip drew around 0.5 amps when set to a normal listening volume. What's the simplest solution? Just browsing around digikey revealed several dc-dc step-up converters and charge pumps, etc. The only problem was that they were all rated for very low current application (i.e. tens to a few hundred milliamps).

I realize that using a smaller pack and multiplying the voltage will result in limited usable time per charge, but it seems like it might be worth a shot. The 12 cell NiMH packs are great for battery-life, but they're a little big and expensive.

Thanks!
-Chad

[AndrewT]

In general all batteries offer cheaper power when using one larger cell
In general all batteries offer more energy /unit volume and /unit weight when using one larger cell.

The result of that, is that using a DC to DC converter chip to generate 3V/6V/9Vdc from a 1.5V single cell is usually lighter and smaller and ends up cheaper to operate.

[scwhiteley]

Thanks Andrew

That's definitely a direction I would like to explore. Any thoughts on a simple voltage multiplier circuit or IC that could provide enough current to power the TPA3110D2?

Thanks again,
Chad

[scwhiteley]

Maxim makes some step-up DC DC ICs for laptop displays. I'm thinking of giving the MAX17112 a shot, as it's in stock at Digikey.

datasheet here:

http://datasheets.maxim-ic.com/en/ds/MAX17112.pdf

[gootee]

There are almost too many to count. I would use either Linear Technolgy or National Semiconductor stuff. If you go to national.com and select the Webench on-line app, you can put in the specs and it will give you a list of appropriate chips and design a complete power supply automatically, for the one you select. At linear.com, the free LTspice used to do the same thing (and still might), by selecting File then Switch Selector Guide. Both sites have TONS of application notes with DC-to-DC converter (aka switchmode power supply) schematics. And there are many, many chips that can easily do 5 to 10 amps. So your current and power requirement should be absolutely no problem, in that sense.