What is it?
Two boards for general-purpose LM317/LM337 power supplies with three rails, useable for many low-power applications where both a +/- supply and an auxiliary voltage are needed. Examples include analog amplifier + digital/logic circuitry, microphone preamplifier + phantom voltage etc.
There are two versions, one where the +/- voltage is derived from a single AC-voltage via a doubler and one where it comes from a traditional two-bridge rectifier circuit. This design is virtually a copy of my GP-PSUs. I made some minor enhancements and added the extra rail, but it is the same basic design.
How big are the boards?
Both board versions measure 3.925″ x 2.6″ (app. 100 x 66 mm.) and they are mechanically interchangeable.
What is the status of the boards?
The “standard” board is in v1.0 and works fine. The voltage-doubled board is in v1.1 and also works fine. The two versions are completely identical except for the diode/bridge arrangement on the +/- supply. The difference in version numbers came because I originally prototyped a different (smaller) layout for the voltage-doubled version. After making the “standard” version that requires a bit more space for the rectifier bridges, I decided it was smarter if they were both the same size and then changed the layout of the voltage-doubled board to match.
Does it use any special/expensive/hard-to-find parts?
Nothing, really. As always with these circuits, you can use standard LM317/337 regulators or splash out on more expensive (low-dropout) types like the LT/LM/LD108x-series. My experiences with the latter parts aren’t the greatest though (instability), so unless your applications require the low-drop capability I’d just as well stick to standard 317/337-types from a reputable source. If your application requires higher performance than this, you are probably better off looking at entirely different circuits and regulators.
Anything else I need to know?
- There is a jumper on the boards that links the ground on the AUX-voltage to the midpoint (0V) of the +/- supply. This is optional and probably not required for most applications but can be used for e.g. linking analog and digital ground in mixed-signal circuits.
- The diameter of the main filter capacitors is 16mm on the AUX supply and 18mm on the main supply.
- The DIP rectifier bridges exist in versions up to 2A rated current although anything more than 1A can be a bit difficult to find. Realistically though, if you plan on drawing more than 1A from either supply the SK104-type heat sinks are probably going to be a limiting factor anyway.
- Mounting the regulators and heat sinks is a bit of a faff because there is not much space, especially if the heat sinks are 38mm or taller. My suggestion (as always) is something like this:
1) Loosely assemble the regulator, the isolation components and the heatsink.
2) Mount the combination on the PCB and solder the heatsink in place.
3) Tighten the screw holding the regulator to the heatsink.
4) Solder the regulator in place.
Download design files here
Even though the regulators used here are generic types made by many manufacturers, there can be small differences in recommended parts values etc. I suggest you always consult the regulator data sheets from the specific manufacturer.
Note: Always read the “intro post” for additional important information about my designs.