A Cheap Yet Useful Transformerless Power Supply Circuit Explained

A very compact transformerless power supply circuit is explained here using the concept of capacitive reactance for stepping down the input AC mains voltage. The idea is cheap yet very effective for applications that require low power for their operations.

Using a transformer in DC power supplies is probably quite common and we have heard a lot regarding it.

However one great disadvantage of using a transformer is that you cannot make the unit compact.

 Even if the current requirement for your circuit application is low, you have to include a heavy and bulky transformer making things really cumbersome and messy.

The transformerless power supply circuit described here, very efficiently replaces a usual transformer for applications which require current below 100 mA.

Here a high voltage metalized capacitor is used at the input for the required stepping down of the mains power and the preceding circuit is nothing but just simple bridge configurations for converting the stepped down AC voltage to DC.

The circuit of a cheap transformerless power supply shown in the diagram above is a classic design of a transformer less power supply circuit and may be used as a 12 volts DC power supply source for most electronic circuits.

However having discussed the advantages of the above design, it will be worth focusing on a few serious drawback this concept may include.

Firstly, the circuit is unable to produce high current outputs, but that won’t make an issue for most of the applications.

Another drawback that certainly needs some consideration is that the concept does not isolate the circuit from dangerous AC mains potentials.

 This drawback can have serious impacts for designs which have terminated outputs or metal cabinets, but won’t matter for units which have everything covered up in a non-conducting housing. However new hobbyists must work with this circuit very carefully to avoid any electrical casualty.

The last but not the least, the above circuit allows voltage surges to enter through it, which may cause serious damage to the powered circuit and to the supply circuitry itself. 

However in the proposed transformerless circuit design this drawback has been reasonably tackled by introducing a high voltage capacitor after the bridge. This capacitor grounds instantaneous high voltage surges, thus efficiently safeguarding the associated electronics with it.

WARNING: THIS CIRCUIT IS NOT ISOLATED FROM MAINS AC, THEREFORE ALL ITS POINTS ARE EXTREMELY DANGEROUS TO TOUCH WHEN CONNECTED TO MAINS AC........

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