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
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.