The power supply shown below is used to supply continuous voltages between 3 and 12 V to small devices whose current consumption does not exceed 100 mA. As it is a “direct” source, that is, without isolation from the power grid, only appliances that are enclosed in insulating boxes should be powered. This power supply uses very few components and does not require a transformer. The output voltage will depend only on the chosen zener diode. Note that the absence of the transformer represents the danger of shocks in case of contact, which is why it is very important that it be installed in a plastic box. The assembly is very simple and there is a protection in case of short-circuits, which is the fuse. If this fuse blows, the indicator lamp will light, indicating the need for replacement. Capacitors C1 and C2 are important in this circuit. The original version requires 1 uF polyester capacitors (do not use any other type) with a working voltage of at least 250 V if the network is 110 V and at least 400 V if the network is 220 V. Diode D1 is the 1N4004 if the network is 110 V or 1N4007 if the network is 220 V. The position of the zener diode, which must be 1 W must be observed, having as reference the range in the enclosure. To connect to the powered device, use a cable with an appropriate plug, observing the polarity or even two wires with different colored clips if the powered device does not have a connector for external power. Before using the power supply, measure the output voltage with the multimeter to make sure it is correct.
