USB Power Supply for Breadboard

Build a fused power supply for breadboard that gets its power from the USB port and provides 5V at high current and 3.3V.

Breadboards are very useful for quickly building electronic circuits. But these circuits require power. The popular breadboard power supply you will find on the market is powered from more than 8 V by an AC-DC adapter. They can provide both 5V and 3.3V from linear 1117 regulators. These regulators can supply a maximum of 800mA, but because they work in linear mode and the PCB is not well built for heat dissipation, the current you can draw from such a device is very limited.

While trying to interface a gas sensor and a TV card tuner to an Arduino, I found that I had troubles powering them. Each of the mentioned devices need about 200mA. Both Arduino and the breadboard power supply use linear voltage regulators to provide 5V. I tried to use the breadboard power supply, but the regulator became hot immediately. Being fed with 12V, the 1117 regulator needed to dissipate (12 - 5) x 0.2 = 1.4 W. That's a lot for its small package.

I needed a better power supply. And I want it for breadboard projects. USB seems to be a pretty good power source, being able to provide at least 500mA. So I designed my own power supply. Since is USB powered, I thought it would be a good idea to have an USB port where I could plug development boards, without needing another computer USB port.

The mini USB is connected to the regular USB, so you can plug a development board, an USB to serial TTL adapter or a programmer straight in it. Therefore, this board features a working USB port, unlike the others. The power line is protected by a fuse. The same power line turns on an LED and provides power to the 3.3V regulator. You can switch from 5V to 3.3V by setting some jumpers, just as you do on common breadboard power supplies.

USB breadboard power supply schematic

The schematic is very simple. I chose a 2A fuse, although 1A may be better suited. Different motherboards can supply different USB currents. And all of them should be short circuit protected. The LED current is limited by 1k resistor. That's more than usual for 5V, but since all today's LEDs are too bright, I could have used even a greater resistance.

I designed two different PCBs. One of them uses the SMD linear regulator 1117-3.3, just as the schematic. The second one, is for a through hole regulator. You can use the LM3940 with a small heatsink on it.

PCB for USB breadboard supply

Three jumpers are placed on pinheaders to modify voltages. The pinheaders near breadboard's power lines control voltages on that lines between 5V, OFF and 3.3V. The third pinheader is placed near the USB connector and is used to enable or disable power in that socket. Remember that data lines between mini USB and USB-A are always connected by tracks.

Since I wanted to build the PCB myself, I designed it with one copper layer. Still, 4 wire jumpers are needed where tracks couldn't pass. The copper layer is on top of the board, for SMD components. If you build the PCB at home, without vias, some of the THT parts will be difficult to solder.

The PCB is designed in KiCAD and pinheaders for breadboard are aligned according to BREADBOARD_SPACING from SparkFun libraries (CC BY license). I realized that this footprint places pins a little more apart than the ones from Chinese MB102 power supply. Still, they fit on the breadboard.

Differences between MB102 supply

I also transferred silkscreen on my PCB, using toner print on special paper. The toner adhered well on areas with copper, but not very good on the etched areas. This happens because etched areas are copper thickness lower and when heating the toner I can't apply pressure on them.

Soldering top through hole parts to the top layer proved to be a challenge. You should make sure that no metallic undersides of parts touch the tracks. If this happens, you can place an insulator between part and PCB tracks.

Pinheaders are easy to solder. You have to push the pins through the black plastic holder, solder them and push back the holder.

Solder pinheaders on top layer

The THT USB connector proved to be impossible to solder. So, I took some short copper wires, passed them through the holes and soldered them on top, near the holes. Then I placed the connector and soldered its pins to the wires, on the bottom.

Soldering USB connector on top layer

This is ugly, but it works. A PCB with vias is highly recommended.

Using the USB power supply for programming a STM32 board

Above is an usage example of the power supply for a STM32 board. You can program the board and power peripherals from the same USB cable.

Downloads: KiCAD project.