Voltage doubler

A voltage, indicated as a voltage doubling also are in electronic form, a charge pump of which achieve a voltage multiplication means of capacitors and diodes. And by using a supplied AC voltage magnitude, a higher DC voltage than can be achieved with a rectifier.

• 2.1 Villard circuit
• 2.2 Greinacher circuit
• 2.3 Delon circuit

General Function

In contrast to the charge pump, which are supplied with DC voltage and the DC-DC converters (English DC-DC converter) to be counted, they have, due to the alternating current supply no oscillator, and a switch are usually electrically controlled switches, such as diodes are used.

The AC voltage can be determined initially charged capacitors and are connected in the second half-wave through the changed polarity of the input voltage in series with each charge pump such as during the first half-wave, resulting in a higher output voltage is obtained. The structure of the voltage doubling cascade elements, very high DC voltages may be generated. These circuits are referred to as high voltage cascade. The DC voltage produced in magnitude is always greater than the peak value of the applied AC voltage.

Benefits

The advantage of a voltage doubler instead of using a transformer with a correspondingly high turns ratio and subsequent thereto rectification consists in the following points:

• A transformer for galvanic isolation is often used as a power source on the input side. This does not have to be designed for the high output voltage with the insulation, the winding design and manufacturing.
• For rectifiers in a cascaded design is the high output voltage is distributed to a plurality of diodes, which they must have a lower blocking voltage as a rectifier for a stepped-up AC voltage directly.
• Under certain conditions, the rectifier cascade is lighter than a transformer
• In a multistage cascading principle, any partial voltages are tapped

Disadvantages

• There is no electrical isolation between input and output
• If electrolytic capacitors are used, they may lose capacity after years

Types

The following are some of the most important voltage multiplier is presented.

Villard circuit

The Villard circuit is a basic circuit consists of a capacitor C and a diode D, as shown in the adjacent circuit diagram. The transformer is funktioniell not absolutely necessary: It is used for electrical isolation and to the AC input voltage be increased to a high alternating voltage to power the Villard circuit.

The Villard circuit represents a clamping circuit: After a few cycles of the capacitor is charged to the peak value of the AC voltage supplied by the transformer secondary side. The voltage supplied by the transformer is shown in the voltage diagram on the left. After a few periods, the output voltage Vout oscillates between 0 V and shown to twice the value of the secondary AC voltage as in the diagram at the right time.

By reversing the polarity of the diode D, a negative output voltage can be obtained.

Greinacher circuit

The Greinacher circuit is an evolution that extends the output side peak voltage of the Villard circuit by an additional diode D2 and a storage capacitor C2 and thus provides a DC voltage with a comparatively small ripple current. The output voltage is in the unloaded state:

To the secondary side than the peak voltage of the transformer Tr and UD as the forward voltage of two diodes, which is the case of silicon diodes, for example 0.7 V per diode.

The circuit was designed by Heinrich Greinacher in 1913 in Zurich and published in 1914. For the operation of its ionometer he needed a DC voltage of 200 V to 300 V, for which the then available in Zurich alternating voltage of 110 V was too low.

The development in the form of a cascade is referred to as a high voltage cascade or sometimes also as Villard circuit. They found, for B in the high-voltage section of a CRT television or in particle accelerators such as the Cockcroft -Walton accelerator application. John Cockcroft and Ernest Walton in 1932 developed this circuit regardless of Greinacher for this accelerator.

Except for the input capacitor, all components must be rated for twice the peak voltage value of the supply voltage.

Delon circuit

The simple Delon circuit is also a voltage doubler and one of the bridge circuits. The positive half cycle through the diode D1 charges the capacitor C1, to the peak value of the secondary side AC voltage, while the diode D2 is blocked. The negative half wave charges via the diode D2, the capacitor C2 to the peak value of the secondary side AC voltage. The output voltage is the sum of the direct voltages on the two capacitors to the value:

The Delon circuit has a special significance for electrical appliances which are to be operated at the usual in America mains voltages of 110 V and the current networks in Europe with 230 V and do not have a wide-range input. In this case, the primary-side bridge rectifier is extended by the Delon circuit: For operation with 230 V, Delon circuit only the bridge rectifier is disabled and active, which provides a Ausgangssgleichspannung of about 325 volts. Operating at 110 V, the intermediate tap between the capacitors of one of the AC inputs is connected by a switch. Due to the voltage doubling is due to the series circuit at approximately the same level of DC voltage of 315 V. Connected to them primärgetakte switching power supplies can always be operated with input voltages of about 315 V is independent from the different mains voltages.

Delon the circuit can also be used for quadrupling. This allows the output voltage to the value

Be increased.