The AC mains signal is a very high voltage at 220V or 230 volt with frequency of 50 or 60Hz. This signal is not used from driving DC circuits. To convert this AC signal to DC of constant current we need a circuit. The following figure shows the circuit schematic of such converter.

constant current circuit

The required converter circuit is the one within the blue box. The ac main signal is first downconverted in magnitude by the Transformer from 230V to 6V or so. Then this 6V AC signal is rectified by the bride rectifier made up of the four 1N4001 diodes. The signal at the output of this bride is a 6V DC signal. Then using the combination of the transistors, resistors and the RED Led we create a constant current source. The transistor used is BC461 but you can also use BC328. The value of R1 should be changed to get different constant current at the output(load). The value of R1 of 10Ohm gives you 100mA, 2.2Ohm gives you 500mA, and value of 1Ohm gives you 1A.


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