AD_Power
A Power Conditioner for Audio Damage Eurorack modules.
Background
At one time Audio Damage manufactured and sold a line of Eurorack synthesizer modules which provided a range of unique functions. Many of these modules are based on the STM32F4 series of microcontrollers and suffer from a power sequencing issue that causes the CPU to hang up when powered from some types of power supplies. It doesn't happen with just any supply, but if you happen to use one that causes the issue it can be quite frustrating.
The problem arises when the -12V rail stabilizes more slowly than the +12V rail - a sneak path through the input buffer op-amps and codec power supply locks up the MCU in a way which cannot be recovered without power cycling. The only way to prevent this without modifying the module is to insert a switch into the +12V rail and hold it off until the -12V rail stabilizes.
I have prototyped a small PCB with the proper circuitry for this which can be added into the power supply cable. The design info is available here if you are able to DIY such things. I do not manufacture or sell these myself.
Hardware
The design is very simple, consisting of just a board, two connectors and four SMT components. The theory of operation is simple - a P-channel MOSFET in the +12V rail is held in the OFF state until the -12V rail drops low enough to turn it on, the threshold for this is set by a zener diode and several resistors.
The bare board looks like this:
and is available from OSHpark for a small fee.
alternatively, the raw gerber files for the PCB are here:
The Bill of Materials (BOM) is here:
It's essential to use the specified components to ensure proper sequencing of the power supplies.