Universal 78xx power supply

The average model railroad uses several electronic circuits. And many of those need a decent DC voltage to work. However most model railroad transformers provide an AC voltage for accessories. The often used 78xx voltage regulators series and a handful of components is all you need to turn the AC voltage into a stabilised DC voltage. For example: to power an IR detector.

The output voltage is defined by the voltage regulator you use. A 7805 delivers 5 Volts, a 7809 9 Volts and a 7812 12 Volts, etc. A few extra components are needed to make the voltage regulator function properly. The AC voltage is fed through a rectifier bridge and flattened by a couple of capacitors. A small LED attached to the output signals when the power supply is switched on.

The input voltage can be up to 35 Volts. The higher the voltage, the hotter the regulator will get. The 78xx needs to be equipped with a heat sink to prevent it from overheating. The minimum input voltage is 2 Volts over the desired output voltage. The maximum current is 1 A.

Parts
Count	Description	Conrad #
1	7805, 7809, 7812, etc.	179205, 179191, 179230, etc.
1	rectifier B80C1500	501441
1	capacitor 2200 µF 25V	445153
2	capacitor 100 nF	453358
1	LED 3 mm	184713
1	resistor 1,2 kilo Ohm*	403261
2	screw connector 2-poles	729949
1	heat sink for 78xx	188271

* Value depends on the output voltage: 5 Volts about 330 Ohm, 9 Volts about 820 Ohm.

Boards are available from the shop.

2011