Building a Power Supply: Phase 1

Well, as alluded to in earlier posts, I have been working on a project over this winter break. I am designing and building a three-output adjustable linear bench power supply. I think that about 2 people who read this will have any idea what that means, so here’s the basic idea: If you want to skip all the back-story, please just take a look at the pictures instead. 🙂

Most engineers are engineers because they really like to tinker with things. Maybe that isn’t actually true of “most” engineers, but I think it’s true of all the cool engineers. 🙂 Anyway, electrical and computer engineers tend to like to tinker with electronics. For instance, this strange tinkering bug might possess them to build a cable to link their universal remotes to their computer for brain surgery. The end product of which, might, perhaps, allow the remote to display “MythTV” (why that?) on screen instead of “TV” or “VCR”…

…Not that anybody you know would do that…

Anyhow, in the course of messing with electronics, you need a fair number of tools. A digital multimeter to show you how many volts something is at, or how much resistance is in a given wire, is absolutely essential. So is a soldering iron to make changes to circuits. (mad scientist’s evil grin >:-D)

Another essential is some sort of power source. That’s where my project comes in. Most devices you buy (think digital camera, cell phone, remote control, answering machine, electric pencil sharpener) have either batteries, a wall plug, or a combination of both as a power source. Generally, devices which have a wall plug (such as your cellphone charger) convert the AC electricity in your house to DC electricity, like that which comes out of a battery. That’s all well and good, and every device is customized to use whatever precise form of DC voltage it needs, but what about building your own devices? Or powering up broken stuff? You (the electrical/computer engineer) would have to have one of every kind of power source, or at least the most common types, on hand.

Enter my adjustable bench power supply. (You knew that whole mess was going somewhere, right?) This is (/will be) a device that plugs into the wall, and converts the AC electricity available there into DC electricity at any voltage. Thus it can be made to work with any circuit’s needs. There are limits of course, though I haven’t completed enough of my construction to know the final specs yet. I expect to be able to provide about 1.0 amp at 1.5V to 30V from one output, and 1.0 amp on each end of a tracking ±1.5V to ±15V. Non-EE Translation: the supply will have three outputs. The first will be able to simulate anywhere from 1 to 20 AA batteries in a row, including “fractions” of batteries. The second output will be able to simulate from 1 to 10 AA batteries (adjustable separately of the first output). The third output will be adjusted simultaneously with the second, and will provide negative1 to 20 AA batteries, at the exact same voltage as the second output. I.e., if the second output is +9.5V, then the third will be -9.5V.

So enough nerd-babble. All anybody really cares about is pictures, right? Fine. Since I’ve only been prototyping for one day so far, I have only tested part of the final circuits. (For the electrically-inclined, I haven’t included the transformer or rectifier stages yet.) BUT, here is what I have so far:


This is the simplest adjustable voltage supply. The little blue box is the control (a potentiometer). Proof that it works [468K MPEG4]


This is the next iteration, with a digital circuit, a pushbutton switch, and three preset voltage levels. I’m rather pleased with how this turned out, though I still have some work to do on the switch, as it sometimes switches 6 or more times per button press (for the EEs: I tried using a RC debouncing circuit, until I realized that leaves the voltage level in the no-man’s zone around 1.2V for way too long. Oops. Now I just have a pull-down resistor, and the normally-open switch ties the clock pin on my CMOS 4017 to Vcc.)

Enough of that: I saved the best (IMHO) for last. Proof that this circuit actually does something [520K MPEG4]. In this clip I press the pushbutton several times. Note that the voltage switches from about 3.25V to 5V to 8V, then cycles around again. Also note the LEDs that track which voltage is currently selected 🙂

Alright, I’ve already wasted way more time on this blog post than I meant to. Back to the bench!

One thought on “Building a Power Supply: Phase 1

Leave a Reply

Your email address will not be published. Required fields are marked *