Transformer less AC to DC power supply circuit using dropping capacitor

Production of low voltage DC power supply from AC power is the most important problem faced by many electronics developers and hobbyists. The straight forward technique is the use of a step down transformer to reduce the 230 V or 110V AC to a preferred level of low voltage AC. But i-St@r comes with the most appropriate method to create a low cost power supply by avoiding the use of bulky transformer.Yes, you can construct power supply for your development without a transformer. This circuit is so simple and it uses a voltage dropping capacitor in series with the phase line. Transformer less power supply is also called as capacitor power supply. It can generate 5V, 6V, 12V 150mA from 230V or 110V AC by using appropriate zener diodes. See the design below.

Circuit diagram

Components required

Resistors (470kΩ, 1W; 100Ω)
Capacitors (2.2µF, 400V, X rated; 1000µF, 50V)
Bridge rectifier (1N4007 diodes x 4)
Zener diode (6.2V, 1W)
LED (Optional)

Working of Transformer less capacitor power supply

This transformer less power supply circuit is also named as capacitor power supply since it uses a special type of AC capacitor in series with the main power line.

A common capacitor will not do the work because the mains spikes will generate holes in the dielectric and the capacitor will be cracked by passing of current from the mains through the capacitor.

X rated capacitor suitable for the use in AC mains is vital for reducing AC voltage.

A X rated dropping capacitor is intended for 250V, 400V, 600V AC. Higher voltage versions are also obtainable. The dropping capacitor is non polarized so that it can be connected any way in the circuit.

The 470kΩ resistor is a bleeder resistor that removes the stored current from the capacitor when the circuit is unplugged. It avoid the possibility of electric shock.

Reduced AC voltage is rectifiered by bridge rectifier circuit. We have already discussed about bridge rectifiers. Then the ripples are removed by the 1000µF capacitor.

This circuit provides 24 volts at 160 mA current at the output. This 24 volt DC can be regulated to necessary output voltage using an appropriate 1 watt or above zener diode.

Here we are using 6.2V zener. You can use any type of zener diode in order to get the required output voltage.

Design

Reactance of the capacitor,

where f is the supply frequency and C is the capacitance.

If the supply frequency is 50Hz, then reactance of 2.2µF X rated capacitor is given by,

So output current,

You can design your own supply if you need high current rating other than 159mA by choosing different capacitor values.

Pin outs of Capacitor, Diode, Zener diode etc

Remember:

Do not touch at any points in the circuit because some points are at mains potential. Keep away from touching the points around the dropping capacitor to prevent electric shock, even after switching off the mains. Great care should be taken to construct the circuit since there is no isolation between mains and our circuit. Adequate spacing must be given between the components.

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