The following power supply serves to provide continuous voltages between 3 and 12 V to small appliances whose current consumed does not exceed 100 mA. As it is a "direct" source, that is, without insulation of the power network, only devices that are enclosed in insulated boxes must be fed.
This power supply uses very few components, and does not require a transformer. The output voltage will only depend on the chosen zener diode.
Check that the absence of the transformer represents the danger of shock in case of contact so it is very important that it is installed in a plastic box. The assembly is very simple and there is a protection for the case of short circuits that is the fuse.
If this fuse blows, the indicator light will light, indicating the need for replacement. In figure 1 we have the complete diagram of this source.
In figure 2 we show the assembly on a terminal strip, which must be installed in a plastic box.
The C3 capacitor is responsible for filtering the source and should be as large as possible. If audio devices such as small radios, amplifiers, transmitters, and snorers are fed, then this component needs to be larger. Values up to 4 700 uF should be tested with minimum working voltage that is twice the voltage of the zener diode used.
Capacitors C1 and C2 are very important in this circuit. The original version requires polyester capacitors (not other type) of 1 uF with a working voltage of at least 250 V if the grid is 110 V and at least 400 V if the grid is 220 V. Diode D1 is 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, with reference to the range in the enclosure.
To connect to the powered device use a plug with an appropriate plug, observing polarity or even two wires with different colored claws, if the powered device does not have a connector for external power.
Before using the power supply, measure the output voltage with the Meter to make sure it is correct. A large heat difference indicates problems with the zener diode or capacitors. Never attempt to power appliances whose consumption is greater than 100 mA.
Material list
D1 - 1N4004 or 1N4007 - rectifier diode - see text
DZ - 3 V to 12 V x 1 W zener diode
NE-1 - common neon lamp
C1, C2 - 1 uF x 250 V or 400 V - polyester capacitors - see text
C3 - 1000 uF - electrolytic capacitor
R1 - 1 M ohm x 1/8 W - resistor - brown, black, green
F1 - 200 mA to 500 mA Fuse
More:
Power cable, terminal bridge, mounting box, fuse holder, wires, solder, etc.
