Adjustable Breadboard Supply


adafruit industries’ latest product is an adjustable breadboard power supply kit. We’ve seen breadboard supplies before, but like most of adafruit’s kits, this is the best design you’re going to encounter. It uses an MIC2941 voltage regulator instead of the more commonplace LM317. It has a very low dropout which means your output voltage can be much closer to the input voltage. Their example is using 3AAA or a Li-Ion battery for an output of 3.3V. Input can be through a barrel jack or terminal blocks. There is a selection switch for 3.3, 5, and adjustable voltage. Using the adjustment pot you can select an output voltage anywhere from 1.3V to within .5V of the 20V maximum input. The adjusted output voltage will remain the same even if you increase the input voltage. Like all of their kits, you can find schematics, assembly and usage instructions, on their project site.

12 thoughts on “Adjustable Breadboard Supply

  1. At $15, that’s a great price for novices who don’t have the knowledge to design/build something like this from scratch. Another well designed and useful kit from LadyAda.

  2. This is not a switching supply design so if you intend to use it for low voltages like 3 or 5vdc , don’t use high input voltage sources like 18-20vdc as it will have to dissipate the difference as heat. Try to pick power sources that are as close to the output voltage that you intend to use.

  3. Well the regulator has only 400mV drop but the protection diode also has a drop of around 500mV at 1.25 amp so using a Li-ion battery won’t work for large currents. It will work without problem for low currents. BTW the MIC2941 has a -20 volt reverse voltage protection built-in ;)

    The 3.3V/5V/Adjustable switch is the best feature IMHO. I think it’s maybe a tad expensive ;P

  4. This is really only marginally useful. Realistically, 85% of the time you will be using 5V. The rest of the time you will be using 1.8V or 3.3V which you probably already have a million regulators for. The only other commonly used voltage is 12V, which you can also use a regulator for.

    A much better solution, IMO, one that doesn’t limit your current or rely on any extra circuitry on your board, is to use an old ATX PSU. You get short circuit prevention, a huge current supply, and a whole lot of different voltages (including negative voltages) to work with.

  5. The ATX power supply is a great idea, and one day I am intending to build a dedicated bench supply from one of those. However, I don’t think it’s a good idea to rely on their internal short circuit protection feature for safety. Modern ATX power supplies are designed to deliver huge amount of current. Therefore, the current threshold that triggers the protection is most likely high; probably high enough to incinerate something flimsy like a prototyping or a bread board into nothingness. Anyone using an ATX supply should attach a current limiter to the output.

  6. it’s perfect for a solar batter charger considering you have a controller.

    I seen a guy do one with a regulator, diode and a national semiconductor LDO to make a 12V regulator that handled hi current. He used it on a portable 12V 48W solar power setup.

  7. Ladyada is using a MIC2941 which as she says in a very low drop out linear regulator. The MIC2941 comes in a 3V and 5V fixed configuration and a Adjustable configuration as well. Sells for about $2.31 on digikey, cheaper if you buy in bulk. You can find the datasheet online. It will give you several recommended circuit designs, one of them ladyada is using, that you can setup your self in minutes on a breadboard.

  8. If this power supply is shorted on the input breadboard pins accidentally it blows parts of the tracks off the board . So much for short circuit protection . Its not there on the input side . On the output side it looks like it relies on the voltage rgulator ‘s built in protection.

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