AC-DC converter is an electronic device use to convert any alternating voltage source (usually sinusoidal) to a dc source. Example of an AC source is a 220-volt that is found in any convenience outlet. The common applications of this device are power supply and chargers that come in different forms and types.

Simple AC-DC converter

The basic circuit of a converter consists of a transformer, bridge diode, and a capacitor.
A transformer is an electrical device that transfers energy from a primary winding to one or more coupled windings by magnetic coupling . In most chargers and power supplies, step down transformer is used.
Another important part of an ac to dc converter is a diode bridge or bridge rectifier, which is an arrangement of four diodes connected in a bridge circuit that provides the same polarity of output voltage for any polarity of the input voltage. Its common application is conversion of alternating current (AC) input into direct current (DC) output.
For many applications, especially with single phase AC where the full-wave bridge serves to convert an AC input into a DC output, the addition of a capacitor is important because the bridge alone supplies an output voltage of fixed polarity but pulsating magnitude .The function of this capacitor, known as a “smoothing capacitor” is to lessen the ripple voltage from raw output voltage waveform from the bridge. One explanation of 'smoothing' is that the capacitor provides a low impedance path to the AC component of the output, reducing the AC voltage across, and AC current through, the resistive load. In other words, any drop in the output voltage and current of the bridge tends to be canceled by loss of charge in the capacitor.

Another type of ac to dc converter is a transformer-less converter that uses only a capacitor and bridge rectifier. Ac source is rectified by bridge diode and dc is fed to load. The voltage of the load is determined by the voltage divider action of capacitor’s impedance and load side impedance. Its advantage converter is lightweight and much cheaper compared to the conventional one.

transformer-less AC-DC converter


  1. How do I calculate the values of the parts needed for the simple ac to dc convertor?

  2. How do I calculate the values of the parts needed for the "Transformer-less AC-DC Convertor" circuit?

  3. For the simple AC to DC converter:
    1. Transformer size or capacity must be equal or higher than your load power requirement. Ex. if your load needs 25VA, then transformer muct be higher than that power rating.
    2. The diode voltage rating must be min 310V reverse voltage breakdown and current rating is
    Current =Transformer Power rating /Voltage in secondary
    Ex. 25VA is power rating and secondary voltage is 12V then your minimu current rating of diode is 25VA/12V = 2.08A
    3. Capacitor value is its up to you, the idea is the higher the capacitance, the better. 220uF, 470uF is ok. But if you need a very clean DC, several thousands of uF is a must.

  4. For transformer-less power supply:
    I don't recommend building this one!!
    This is good only for load 50mA and below, higher than this current make the circuit more expensive (than with a transformer) and very impractical to use.
    Example your load needs a dc supply with 10mA current.Your mains supply voltage is 220V @ 60hz.
    Current =220V/impedance of capacitor Xc @ 60Hz.
    Xc=1/(2*pi*freq*C) ;
    therefore C = 0.12uF

  5. I want to run a 90volt dc gear motor (1/15 hp). I have 120 a.c. so I need to convert it to 90 d.c. with potemeter to control the d.c. voltage out put.

  6. dear sir,

    pls. confirm the final rates and delivery position of
    following items as under :

    110vac to 11ov dc convertor (output 1-5 amp)

    qty 2 nos.

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    ritesh gandhi
    9327 02 1716

    parikh switchgears,
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    phone 079-25504730.31.32 fax .25501434
    email : parikhswitchgear@gmail.com,
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  8. How will be the full wave bridge rectifier when the transformer is like 9-0-9.

  9. AC/DC converters serve as rectifiers. They convert ac to dc in a number of industrial, domestic, agricultural, and other applications.
    Transformer manufacturer in India