I need to build regulator boards for my students to use with their solderless BB's. They will wire chips in backwards and create shorts, this is a given.

Here is what I have in mind. It would provide 5V at 100ma, 500ma, and 1 Amp if the wall wart is up to it.

Brick/wart connects to regulator using screw terminals.
Just after the terminal block a diode to prevent problems when the brick is hooked up backwards. Maybe setup a red LED to indicate this conditon.

Two regulators.

The first will be a LM2931AZ50R .1 amp 5V regulator with reverse voltage and short protection. This regulator will be used when 100 ma is enough, or during initial testing lto ensure there are no shorts or chips in backwards.

The second will be a generic 7805 regulator with 1 amp and .5 amp PTC fuse on the input side. A jumper block selects which of the 2 fuses powers the regulator.

Maybe have the 100ma output sperate from the other. One could use the 100ma source for logic and the other for motors or LEDs.

Suggestion or comments ?

3v0

Thanks for the input.

To make it work with ac/ac would one also need a 22000uf cap in addition to the bridge? Sounds expensive and large.

I am attempting to use wall warts donated by the parents. Hopefuly enough of them will fall into the 12-7 range that will work with the regulators. There is not telling what sort of plugs they will have. But I do like the idea of not having to use the screw terminals.

Originally Posted by nickelflippr

Using 2.5mm center positive jack would be nice touch to keep polarity straight. In my experience they seem most popular at the thrift stores. Also a bridge might be handy just in case someone trys to plug in an ac/ac wall wart.

3v0,

If you get a chance, please look at the Micrel MIC4682 smps 'buck' regulator. It's a 2 amp regulator with current limiting capabilities. The little 1.9"x1.9" evaluation board in the Data Sheet includes jumpers for selecting voltage (1.8, 2.5, 3.3, and 5.0v) and current (0.6a, 1.0a, and 2.0a) and the formulas you would need for coming up with other limit settings.

It may seem like more work and a larger investement on the "front end" but Micrel (MIC4682) and Coilcraft (DO5022P series) will sample and you'll end up with a very versatile SMPS regulator sub-system for your breadboard experiments.

Micrel MIC4682 Product Page

Happy Holidays.

Mike

nickelflippr,
It has been a long time since I built a supply that han an AC input. I may have added an extra zero on the cap.
So few of the wall warts I see are AC out, not a lot of motivation to handle it.

Mike,
I need to build these over break so I will use what I have or can get from Mouser or Newark if a few days.

The Micrel MIC4682 looks like a very nice chip. They have a lot of interesting/useful offerings. I will give these a try.

Also thanks for the kind words regarding the #define 7 seg stuff. We have enough self taught people here that seeing this sort of stuff should be helpful.

3v0