Diode voltage multiplier circuit

- a useful circuit using simple semiconductor diodes that multiplies the incoming voltage for use in power supply and detector circuits

Within a power supply or other rectifier circuit it is possible to configure the diodes in such a way that they double, triple or more, the level of the incoming voltage. This type of voltage multiplier circuit finds uses in many applications where a low current, high voltage source is required. These circuits may also be used in detector circuits where the detected voltage needs to be increased.

Basic voltage multiplier circuit

Although there are some variations on the basic circuit, these ones shown below use a single winding on the transformer that is required, one side of which can be grounded. Alternatively another AC source can be used. In this configuration the circuit is particularly convenient as the AC source does not need to be isolated from ground.

Diode voltage doubler circuit

Diode voltage doubler circuit

In this voltage doubler circuit the first diode rectifies the signal and its output is equal to the peak voltage from the transformer rectified as a half wave rectifier. An AC signal via the capacitor also reaches the second diode, and in view of the DC block provided by the capacitor this causes the output from the second diode to sit on top of the first one. In this way the output from the circuit is twice the peak voltage of the transformer, less the diode drops.

Variations of the basic circuit and concept are available to provide a voltage multiplier function of almost any factor. Applying the same principle of sitting one rectifier on top of another and using capacitive coupling enables a form of ladder network to built up.

The voltage multiplier circuits are very useful. However they are normally suitable only for low current applications. As the voltage multiplication increases the losses increase. The source resistance tends to rise, and loading becomes an issue. For each diode in the chain there is the usual diode drop (normally 0.6 volts for a silicon diode), but the reactance of the capacitors can become significant, especially when mains frequencies of 50 or 60 Hz are used. High voltage high value capacitors can be expensive and large. This may provide physical constraints for making them too large.

By Ian Poole

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