Understanding the Voltage Doubler
Controlling the voltage during the rectification of an alternating current for a D.C requirement is extremely important. In fact voltage control and stabilization is an integral part of any electrical process.
Several types of voltage stabilizers are used to maintain a constant voltage throughout the process of converting alternating current to direct current. For example, if a system is supplied power from a set of batteries, the voltage will reduce when the batteries discharge and thus a backup battery system must be provided for this. The amount of voltage required during the low voltage phase depends on the capacity of the equipment. There are chances that the voltage required for a particular application is higher than the voltage supplied. For such cases, a voltage doubler is used. It is also to note that all electrical equipment requires a level of voltage slightly higher than the normal. This helps in maintaining the efficiency and stability of the equipment.
The voltage doubler is an integral part of the alternating current rectification process and helps in increasing the voltage of the system. As the name suggests, it produces voltage which is almost twice than the input voltage. This means that the voltage generated by the doubler is twice the peak value of the alternative input current. However note that this is possible only if the load current is very small.
Construction and Working
Voltage doubler is basically a circuit, consisting of two semi- conductor PN diodes (rectifiers) and two capacitors, arranged in the form of bridge construction. The capacitors and rectifiers are arranged as shown in the figure.
The two capacitors, C1 and C2 are connected in series with each other and also with the load. In voltage doubler circuit the alternating current will first flow in a clockwise pattern and then in anti clockwise (Indicated by arrows in the diagram). When the current flows in a clockwise direction, the rectifier R1 will charge the capacitor C1 till the voltage reaches the peak of the positive voltage wave. In the similar manner, then the current flows in an anticlockwise direction, the rectifier R2 will charge the capacitor C2, till the voltage reaches the peak of the negative voltage wave.
As both the capacitors are in series with each other and the load, the opposite voltages generated in both of them will add up and discharged to the load. Thus a doubling effect will be produced, delivering a voltage which is twice the input. However, it is to note that the system will work only if the load is very small. In case the load increases, the doubling effect will not be produced.
Similar circuits are used to increase the voltage almost four times the input voltage, but only if the load current is very small. In many applications transformers are also used. However, they are expensive and do not provide the right quality of current.
Voltage doublers are extensively used in television and radar equipments as an alternative to heavier, larger, and expensive transformer and rectifier arrangements, which also perform the same function as that of voltage doublers.
References and Image Credits
Marine Electrical Equipment and Practice by H.D McGeorge