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The Voltage Multiplier

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The advancement of humankind throughout time have resulted in a great leap in different areas including electronics and technology. As time goes by, many gadgets and equipment that makes a man’s work more efficient and improve humanity’s state of being in this world have been made. These electronic devices operate by supplying a power source that could take the form of batteries, power supply, etc. Most of the electronic circuits like amplifiers have only a particular range of voltages wherein they could accept the input signals. Going below the needed amount of input voltage will result to the device’s incapability to operate while exceeding the input voltage above the needed amount will cause distortions in the output of the electronic circuits and may even lead to damage of the circuit components.

We could also observe that many electronic devices in the present work on a single positive supply, in which the input voltage range would also be on the positive side. However, there also exist the natural signals that could take the form of audio signals, sinusoidal waveforms, and many others having the varying amplitude in their duration and contain both positive and negative cycles. The alteration of either the positive peak and negative peak of the input signal to a definite value through shifting the entire signal up or down so as to obtain the output signal peaks at the desired level is needed [1]. The circuit that solves this problem is called a clamper circuit.

A clamper adds a dc level to an ac voltage and is known as a “DC restorer” [2]. Through the use of a clamping circuit, The positive or negative peak of a signal can be positioned at the level desired. A clamper circuit is capable of shifting the levels of peaks of the signal; hence, it is also called as a level shifter [3]. A clamper circuit has two types, a positive and a negative clamper.

The operation of the positive clamper can be observed on the first negative half cycle of the input voltage. The diode will then enter the forward biased state the moment the input voltage initially goes negative. This then allows the capacitor to charge to near the peak of the input as shown on the following figure.

Just right after the negative peak, the diode will then be reverse-biased due to the cathode that is held nearby the charge on the capacitor. In addition, The capacitor can only discharge through the high resistance of RL; and from the peak of one negative half-cycle to the next, there is an only a little discharge in the capacitor. This amount of discharge will depend on the value of the RL of the circuit. Clamping action will be affected the moment the capacitor discharges during the period of the input wave. In the event when the RC time constant is 100 times the period, we could then say that the clamping action is excellent.

A small amount of distortion at ground level will result for an RC time constant that is ten times the period caused by the charging current. The clamping action will result in a net effect of the capacitor retaining a charge that is approximately equal to the peak value of the input less the diode drop. The capacitor voltage acts essentially as a battery in series with the input voltage. The dc voltage of the capacitor adds to the input voltage by superposition as shown in the following figure.

If the diode reversed (turned around), a negative dc voltage is added to the input voltage to produce the output voltage resulting in the negative clamper circuit as shown below.

There is also the case when a reference voltage is added to the circuit. When a positive reference voltage is added in series with the diode of the positive clamper, the following circuit will result.

In this case, the diode conducts, as initially, the supply voltage is less than the anode positive reference voltage during the positive half cycle of the input. The moment the cathode voltage is greater than anode voltage, the diode will then stop to conduct. During the negative half cycle, the diode conducts and charges the capacitor. The output will then result in the figure shown below.

When a negative reference voltage is added, the direction of the reference voltage is reversed, which is connected in series with the diode making it as a negative reference voltage.

During the positive half of the cycle, the diode will be non-conducting. This state is where the output is equal to capacitor voltage and input voltage. On the other hand, the diode starts conduction only after the cathode voltage value becomes less than the anode voltage during the negative half cycle.

The same idea goes for the negative clamper with the addition of positive and negative reference voltage as shown below.

With the positive reference voltage, It is similar to the negative clamper, but the output waveform is now shifted towards the positive direction due to the sign of the reference (+). During the positive half cycle, even though the diode conducts, the output voltage becomes equal to the reference voltage. This results in an output that is clamped towards the positive direction. On the other hand, by inverting the reference voltage directions, the negative reference voltage is connected in series with the diode as shown in the above figure. As the positive half cycle starts, the diode also starts conduction before zero, as a result from the cathode having a negative reference voltage, which is less than that of both the zero and the anode voltage. The result is a waveform that is clamped towards the negative direction. A clamper can be used in several ways and one of its application is on voltage doublers or voltage multipliers.

The Voltage Multiplier is a special type of diode rectifier circuit, which can potentially produce an output voltage many times greater than of the applied input voltage [4]. Voltage multipliers have similarities to a rectifier are in terms of converting AC-to-DC voltages for use in many electrical and electronic circuit applications where a very high DC voltage generated from a relatively low AC supply is needed. One kind of a voltage multiplier is a voltage doubler which can be classified as half-wave and full-wave. A voltage doubler is a voltage multiplier with a multiplication factor of two [5].

A half-wave voltage doubler is shown in the figure above. When the positive half-cycle of the secondary voltage starts, diode D1 will then enter the forward-biased state and D2 is reverse-biased. Capacitor C1 is then charged to the peak of the secondary voltage (Vp) decreased by the diode drop with the polarity shown above. On the other hand, during the negative cycle, diode D2 will now be in forward-biased and D1 is reverse-biased, as shown in the figure below. The peak voltage on C1 adds to the secondary voltage to charge C2 to approximately 2Vp due to the fact that the C1 can’t discharge.

In addition, under a no-load condition, C2 remains charged to approximately twice the value of the peak voltage. C2 discharges slightly through the load on the next positive half-cycle and is again recharged to 2Vp on the following negative half-cycle in the event that a load resistance is connected across the output. The resulting output will be a half-wave, capacitor-filtered voltage. The peak inverse voltage across each diode is again twice the peak voltage. The output voltage across C2 would have the opposite polarity if the diode were reversed. Another type is the full-wave voltage doubler.

D1 is forward-biased and C1 charges to approximately the peak voltage when the secondary voltage is positive as shown above. On the other hand, during the negative half-cycle, D2 will now be forward-biased and C2 charges to approximately to the value of the peak voltage. The output voltage is twice the peak voltage that is taken across the two series capacitors.

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GradesFixer. (2018, October, 22) The Voltage Multiplier. Retrived April 19, 2019, from https://gradesfixer.com/free-essay-examples/the-voltage-multiplier/
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