Microprocessor to battery charger

That regulators only go down to 1V say is irrelevant - just offset the regulator "ground" from the output "ground" by that amount. The output can then easily be taken to zero.

You could, as you suggest, simply link the microprocessor to a D/A and then use the output of that as the analogue voltage reference for conventional (switching or not) regulators.

Or you could use an A/D to sample the output voltage, feed that to the microprocessor and use that to generate the timing signals for a switching regulator. That allows some pretty devious designs(implemented mostly in software) to achieve things that simply aren't possible using the basically analogue approach. You can use a multi-channel A/D to sense all sorts of parameters and design for them. Controlling any number of independent outputs of different types becomes child's play. You can also have a two stage regulator system - a coarse and fine control if you like - to give you fine control over a very wide range using off the shelf components. Each stage of the regulator copes with a different one of the normally incompatible design constraints.

Hi, Here's an interesting programmable switching-mode current source (0 - 5 amps,

0 - 10 vdc output, 36 vdc supply): It uses a 12 bit input command from your micro and maintains the current at the commanded level. Your micro would just need a/d inputs for battery voltage and battery temp (if you want), 12 digital outputs, interface circuitry for the user interface, etc. There's PIC (Peripheral Interface Controller) microcontroller models that could handle all this with no sweat. PICs are designed for embedded applications that require interfacing to real world analog and digital i/o and they are all amazingly inexpensive.

Here's an example of a PIC based NiCd/NiMh home brewed charger using PWM output from the PIC to control an LM317 regulator (but only 1.5 amp load):

See the schematic (Fig.3): Maybe this gives you some ideas. There's MANY ways to implement your project. I highly suggest that, hardware considerations aside, you spend LOTS of time researching the intricacies of the recommended charge algorithms for the various battery types and sizes that you're interested in. Battery charging isn't as cut and dried as many ppl think but you probably already know that. Programming the various charge algorithms can be a lot of fun and doesn't really require a huge amount of memory if done properly (I use assembly language but there are basic and c compilers available as well). For your app. I'd use a more sophisticated controller than the one in the example above - you'll need more memory than he did and memory can present some design challenges with a PIC. The good news is, even high-end PICs are pretty cheap considering their capabilities. The one used in the example costs less than $4.00. You can also interface them to LCD displays, keypads, PCs, you name it - just takes a while to learn the interfacing and programming methods - that's all. Of course there's lots of other brands of micro out there but I'd definitely go the microController route over some microProcessor that's not designed for embedded, real world i/o control.

Cheers, Perion