When doing WSPR on the Raspberry Pi, I needed a bit more current than the standard mobile phone chargers suggested for the Pi could offer. Typically they’re rated at about 1 amp, and will do 500 mA with a clean output supply but much beyond that the output gets noisy and the voltage drops (there are some exceptions). As I was interested in receiving weak radio signals the switching noise from the power supply was a nuisance as was the weird behaviour of some of the peripherals. As you so often see in the Pi forums, “It’s your power supply”.
The design presented here isn’t the greatest or most reliable; it’s the easiest to do the job well. The big 2N3055 transistor used as a series pass transistor is probably overkill for the couple of amps required here, but as it’s well under-rated, it should easily do! It’s important to note that there is no short circuit protection and no over-current protection. Short the output and you’ll get all the current the supply can manage (plus a hot or blown 2N3055). You’ve been warned!
Below is the schematic for the regulator. The design is very simple. U1 is a LM 7805 5 Volt regulator. This provides the 5V reference to Q1 which is configured in series pass – the emitter of Q1 is at 5V but with more current than would be provided by the 7805. Diode D2 gives a slight offset to the reference voltage of typically 0.7 Volts which overcomes the 0.7V loss at the transistor’s base-emitter junction.
Just in case anyone is interested in making this project, I have included the PCB masks.
Below are the download links to the board mask and silk as PDF which can be printed at 100% to provide toner transfer or optical masks. Also included is the Gerber files for milling boards.