LinuxFocus.org: simple DC power supply for your Lab.

# Simple DC power supply

This is a very simple non Microcontroller based DC power supply. The circuit is based on the LM317 Voltage Regulator. It has a fixed current limit of 1A and is ideal to build a very small and universal power supply for electronic experiments at home.
This article has nothing to do with Linux or programming but it is provided as a simple and cheap solution for those who don't have yet a fully stabilized and regulated power supply at home but need one for the other hardware and Microcontroller articles in LinuxFocus.
In addition to the parts shown in the diagram below you will need a transformer with 12V AC output or switched power supply module with 15V or more DC output. If you use a switched power supply module then make sure that it operates already at zero output current.
Click on the circuit diagram for a bigger picture. The values of all the parts are listed in the schematic. The bridge-rectifier must be able to handle 1A. You can also use 4 diodes, e.g 1N4001.

The 0.1uF capacity between earth and signal ground is needed if you have a transformer where one layer of the secondary coil is very close to the primary coil. This results in a very small capacity between primary and secondary side. The current is very low (micro amperes) but 230V (or what ever you have). A human touching the wires will not feel such low currents but sensitive cmos electronic can be destroyed by that. This 0.1uF capacity will fully compensate such currents. It is good to have in any case even if you have a transformer where the coils are far apart or good switched power supply.
Pinout of the LM317 in To220 case:

#### Example: some photos from my power supply

Here the frame of the case. Sheet metal and wood on the sides. In my opinion this is the best and cheapest solution for a "home made" case:
The next picture shows the final power supply with open case. I integrated a small digital volt meter module. That way you can directly see the value of the output voltage. If you plan to do the same, remember that often DVMs can not operate from the same voltage that they measure. These voltages have to be totally separated. If you use only one transformer then you will need a 1W DC-DC converter. Theses DC-DC converters are small integrated circuits and are usually cheaper than a second transformer.

#### References

- datasheet for the LM317
- Eagle schematic, simpleDCpower.sch

© Guido Socher, FDL This is a LinuxFocus.org article.

2002-06-05