Programmable Load 1: Concept, Motivation, Goals

As I think about various projects, I am realizing that what I really need most is some more test gear to help me discover and diagnose problems, which will inevitably occur.  I have a multimeter and a cheap Chinese digital oscilloscope (as well as an ancient rather limited analog scope), and a pretty nice RCL meter, but I feel as if I would become more effective if I had some more tools.

One useful tool that should be a reasonably simple project: a programmable load, to help test power supplies (both the lab supply I wrote about the other day and also the sort of routine power supplies that virtually every project needs.  I think this will be a good "first homebaked test gear" project to see through to completion, so it's time to begin!

The idea, of course, is to load down Circuits Under Test with some programmed current value so their behavior can be examined for proper operation.  For the most part, the most useful currents will be of "medium" size... from tens of milliamps to maybe an amp.  Additionally, I would like to be able to fairly accurately program in much lighter loads, down to under a milliamp, in order to:

• Check the behavior of supplies in a "barely loaded" situation
• Characterize the behavior of circuit elements besides power supplies in normal sorts of situations.

It would be handy (because of my interest in motor control) to have a much beefier programmable load, but I will leave that for another day so I don't get bogged down in the difficulties of high-power circuitry.

Additionally, there's a few other features I want:

1. The ability to test transient response, from sudden increases or decreases in current demands.
2. The ability to test a supply's behavior in response to "pulsed" current demands.

Those extra features shouldn't cause too much difficulty (at least I don't think they will), but they are more complicated to set up -- which means that a simple "one knob" user interface won't do the trick.

When that happens (which is most of the time, I think!), I really want to make sure to do a good job with the interface (I will add a separate rant about that subject when I'm done writing this).

It seems as if most of the projects I want to work on want some sort of display that is more than just a number.  And it also happens that I am interested in display devices.  So, part of this project will be to bite the bullet and grow stronger by having a good set of skills, methods, and tools for using displays in projects!