This tutorial shows how to build a power supply that does not use a transformer, and can provide around 70 mA of current, at a voltage set by the zener diodes that you choose.\r
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In a normal power supply, a transformer is used to lower the mains voltage, and also to limit the current. In this power supply, we use a capacitor and a resistor, that together form an impedance that lowers the current from the mains. The voltage is set by a bridge rectifier that includes two zener diodes that set the voltage to a desired value. Finally, there is a capacitor at the output, that filters the current.\r
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The main disadvantage of transformerless supplies is that they dont offer issolation from the mains voltage line and present more of a safety issue.\r
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If your mains voltage is 220V, you can use a 470 Ohm resistor and a 1 uF capacitor.\r
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Please be carerful when using this circuit.