TREE

An increasing number of appliances draw a very small current from the power supply. If you need to design a mains-powered device, you could generally choose between a linear and a switch-mode power supply. However, what if the appliance’s total power consumption is very small? Transformer-based power supplies are bulky, while the switchers are generally made to provide greater current output, with a significant increase in complexity, problems involving PCB layout and, inherently, reduced reliability. Is it possible to create a simple, minimum part-count mains (230 VAC primary) power supply, without transformers or coils, capable of delivering about 100mA at, say, 5 V? A general approach could be to employ a highly inefficient stabilizer that would rectify AC and, utilizing a zener diode to provide a 5.1 V output, dissipate all the excess from 5.1 V to (230×√2) volts in a resistor. Even if the load would require only about 10mA, the loss would be approximately 3 watts, so a significant...

This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC. Always use a fuse and/or a fusible resistor to be on the safe side. The values given are only a guide. There should be more than enough power available for timers, light operated switches, temperature controllers etc, provided that you use an optical isolator as your circuit's output device. (E.g. MOC 3010/3020) If a relay is unavoidable, use one with a mains voltage coil and switch the coil using the optical isolator.C1 should be of the 'suppressor type'; made to be connected directly across the incoming Mains Supply. They are generally covered with the logos of several different Safety Standards Authorities. If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts. The low voltage 'AC' is supplied by ZD1 and ZD2....

Description: This circuit will supply up to about 20ma at 12 volts. It uses capacitive reactance instead of resistance; and it doesn't generate very much heat.The circuit draws about 30ma AC.If you need more current, use a larger value capacitor; or put two in parallel; but be careful of what you are doing to the Watts.  The low voltage 'AC' is supplied by D1 and D8.Also you can replace R3 and D3 with a 78 Series regulator. Schematic:     Components:   u1,   100ma fuse    R1,   100 ohm ,  0.25watt    R2,   1K ohm,   2 watt    R3,   1k ohm ,  0.25watt    C1,   470nF,  400v, polyseter    D4-D7,   1N4001 or 1N4007    D1, D8,   16v Zener Diode    C2,   1uF  electrolyte    D2,   12v Zener Diode