Proto PSU is an easy to assemble DIY kit which can either be a breadboard attached supply, an internal Eurorack case supply, or a Eurorack module style power supply depending on how you configure it.
This power supply has been designed as an easy and low-cost solution to have a dual rail power supply typical of DIY synths for prototyping purposes. The design uses all through-hole components that are clear and easy to solder. There is no need for a specialist AC supply or to use mains electricity as it runs off a 15VDC adaptor (not included).
The PSU can supply a shared current of 300mA between the 12V and 5V rails, and 100mA on the -12v rail. If you want to use the PSU to power a small Eurorack case then add the Power Extension Busboard for an extra 8 x headers.
Caveats and Warnings
It is not only called “proto” because it is for prototyping but also because it is just a test PSU you use before you attach your design to a bigger nicer one. There are a few limitations that you need to be aware of just so it meets your expectations.
- Current is limited to 100mA for -12V and 300mA for both 5/12V. The polyfuses will blow if this is greatly exceeded (a short), don’t worry they will reset.
- The switching supply IC is supposedly an 80s design, that’s how it was possible to get a DIP-8 part, it is probably the closest to a jellybean DC converter you can get. It switches at approximately 100kHz which will be audible at higher loads near 100mA of the -12V rail. You must follow some good design practices (that you should be doing anyway!) such as not directly connecting voltage references to the rail. For example with op-amps when you need an offset voltage or pot reference.
- The nature of polyfuses means that if you only slightly exceed the 300mA current the fuse might not open completely, it could cause the voltage to droop but not go low, this may cause frustration if you are unaware, keep measuring rails.
- When using it in Eurorack module configuration take care to notice that the tag of the regulators are bare and may touch something.
- Additionally, the polyfuses have a resistance, any circuit that pulls power in pulses will make the line noisy, if this is an issue either short them or remedy with a capacitor.
This module uses no dangerous parts but if not built properly or is over driven very slightly it will get very hot and burn your fingers. Make sure the core components are all properly installed in the right place and polarities are correct. The polyfuses are for protecting against shorts but not for over currents, if for example the -12V rail is driven over 100mA but below 500mA the MC34063 will get very hot and so will the 7912 regulator.
Proto PSU – Build Document
- Width: 6HP
- Depth: 50mm
- 12V and 5V shared current : 300mA
- -12V : 100mA
- 100mV ripple