120V / 12V 1.4A PSU 2014-02-21

For a project where off-the-shelf switching power supplies all had too much coil whine, I designed this linear power supply. It is noise-less, and runs silently. It is designed to be plugged into mains, with proper creepage/clearance zones, but you have to use a separate fuse in the power entry module for the grounded box you should mount this in.

Output voltage is set by the R2/R1 divider; the transformer and application I use set this at 12.0V.

If you’re not comfortable designing for and working with mains voltage electronics, I recommend against trying this project.

LiPo low-voltage cut-off 2014-03-24

After destroying a LiPo battery when forgetting to turn off a LiPo powered Raspberry Pi device, I built this circuit. It features a soft-power-on switch based on a P-channel MOSFET, and a space for an ATTiny85 to monitor voltage and turn off when it’s too low.

I have built this and use it, and I additionally talk to the ATTiny85 using the SPI in the Raspberry Pi (without chip select) to report voltage to the host, and do soft-power-off on demand.

Firmware for the ATTiny85 obviously is important for this project to work right!

20140420 P-channel Power Switch

This switch features pushbutton on and off action, as well as ability to actuate on and off through the 100-mil header. Power handling up to 20A, depending on specific P-channel MOSFET used and tolerance for board heat.

I have ordered, built, and tested this design, and it works well. Leakage current when off is below what I can measure – approximately equal to zero.

Revision A 2014-08-23