A voltage multiplier is one of the simplest ways to obtain a high voltage if you need it. A rectifier that transforms an AC voltage to a higher DC value is a voltage multiplier. Heinrich Greinacher invented them in 1919, and they were used to create the first artificial nuclear disintegration particle accelerator, so you know they’re serious.
In theory, the multiplier’s output is an integer multiple of the AC peak input voltage. While voltage multipliers can function with any input voltage, their primary application is when extremely high voltages in the tens of thousands or even millions of volts are required. They have the advantage of being relatively simple to construct and less expensive than a comparable high voltage transformer with the same output rating. A voltage multiplier may assist you if you require sparks for your crazy science.
What Is A Voltage Multiplier?
For many years, voltage multiplier power supplies have been employed. In 1932, Walton and Cockroft designed an 800-kV supply for an ion accelerator. Since then, the voltage multiplier has generally been utilized when high voltages and low currents are required. The use of voltage multiplier circuits minimizes the size of the high voltage transformer and, in some situations, allows the transformer to be removed entirely.
Recent technological advancements have made it possible to create a voltage multiplier that transforms low AC voltage into high DC voltage with efficiency comparable to the transformer-rectifier-filter-circuit.
The voltage multiplier is made up of multiple arrangements of capacitors and diodes. There are several stages to a voltage multiplier.
Each stage consists of a diode and a capacitor. These diode and capacitor configurations can create a rectified and filtered output voltage with a greater amplitude (peak value) than the input AC voltage.
Types of voltage multipliers
There are four types of voltage multipliers:
Half-Wave Voltage Doubler
As the name implies, a half-wave voltage doubler is a voltage multiplier circuit with an output voltage amplitude twice that of the input voltage. A half-wave voltage doubler drives voltage to the output during either a positive or negative half cycle. Two diodes, two capacitors, and an AC input voltage source are used in the half-wave voltage doubler circuit.
During a positive half cycle
The half-wave voltage doubler circuit diagram is given in the graphic below. Diode D1 is forward biased during the positive half cycle. As a result, an electric current can pass through it. This current will flow to the capacitor C1, charging it to the input voltage’s peak value, Vm.
However, because the diode D2 is reverse biased, no current flows to the capacitor C2. As a result, the diode D2 prohibits the capacitor C2 from receiving electric current. As a result, during the positive half cycle, capacitor C1 is charged, but capacitor C2 is uncharged.
During A Negative Half Cycle
During the negative half-cycle, diode D1 has a reverse bias. As a result, the electric current will not pass through diode D1.
As a result, the capacitor C1 will not be charged during the negative half cycle. The charge (Vm) stored in the capacitor C1, on the other hand, is discharged (released).
During the negative half-cycle, however, the diode D2 is forward biased. As a result, the diode D2 permits electricity to flow through it. This current will pass to and charge the capacitor C2 because the input Vm and capacitor C1 Vm are added to the capacitor C2, the capacitor C2 charges to a value of 2Vm. As a result, both the input supply voltage Vm and the capacitor C1 voltage Vm charge the capacitor C2 during the negative half cycle. As a result, the capacitor C2 is charged to a voltage of 2Vm.
When the circuit’s output side is connected to a load, the charge (2Vm) held in the capacitor C2 is discharged and flows to the output.
During the positive half cycle, diode D1 is forward biased, while diode D2 is reverse biased. As a result, capacitor C1 charges Vm, whereas capacitor C2 remains unchanged. The charge (2Vm) held in the capacitor C2, on the other hand, will be discharged and flow to the output load. As a result, the output load receives a voltage of 2Vm from the half-wave voltage doubler.
In the next half-cycle, the capacitor C2 is charged again. The output voltage (2Vm) is twice as high as the input voltage (Vm). In a half-wave-voltage doubler, the C1 and C2 charge in alternate half-cycles.
The half-wave voltage doubler’s output waveform is nearly identical to a half-wave rectifier with a filter. The half-wave voltage doubler’s output voltage amplitude is twice the input voltage amplitude, which is the sole difference. The output voltage amplitude equals the input voltage amplitude in a half-wave rectifier with a filter.
The half-wave voltage doubler delivers voltage to the output load (positive or negative half cycle). In our scenario, the half-wave voltage doubler provides voltage to the output load during positive half cycles. As a result, the half-wave voltage doubler’s output signal control is poor.
Full-wave Voltage Doubler
Input voltage is doubled in this circuit, as the name implies. The Full-wave voltage doubler’s functioning is relatively straightforward:
Diode D1 becomes forward biased during the positive half cycle of the Sinusoidal wave of AC, while D2 becomes reverse biased, causing capacitor C1 to charge through D1 to the sine wave’s peak value (Vpeak). D2 is forward biased during the negative half cycle of the sine wave, while D1 is reverse biased, so capacitor C2 is charged through D2 to Vpeak.
With no Load attached, both capacitors are charged to Vpeak, resulting in 2 Vpeak (Vpeak + Vpeak) across C1 and C2. The Full-wave rectifier is the source of its name.
Voltage Triple
The triple voltage can be achieved by adding another diode-capacitor stage to the half-wave voltage doubler circuit.
During the first positive half-cycle
The diode D1 is forward biased during the first positive half cycle of the input AC signal, but the diodes D2 and D3 are reverse biased. As a result, the diode D1 permits electricity to flow through it. This current will travel to capacitor C1 and charge it to the input voltage’s peak value, Vm.
During Negative Half Cycle
Diode D2 is forward biased during the negative half-cycle, but diodes D1 and D3 are reverse biased. As a result, the diode D2 permits electricity to flow through it. This current will pass to and charge the capacitor C2. The capacitor C2 is charged to double the input signal’s peak voltage (2Vm). The charge (Vm) held in the capacitor C1 is discharged during the negative half-cycle.
Capacitor voltage + input voltage = Vm + Vm = 2Vm combines the capacitor C1 voltage (Vm) and the input voltage (Vm) into the capacitor C2. As a result, the capacitor C2 charges to 2Vm.
During the Second Positive Half-Cycle
D3 is forward biased during the second positive half cycle, while D1 and D2 are reverse biased. Because of the negative voltage at X due to the charged Vm across C1, diode D1 is reverse biased, and diode D2 is reverse biased due to its orientation. As a result, capacitor C2 discharges its voltage (2Vm). This charge will travel to C3 and charge it to the same voltage of 2Vm.
The output voltage is taken across the two linked capacitors C1 and C3, connected in series. Capacitor C1 has a voltage of Vm, while capacitor C3 has a voltage of 2Vm. As a result, the total output voltage equals the sum of capacitors C1 and C3, i.e., C1 + C3 = Vm + 2Vm = 3Vm.
As a result, the triple voltage’s total output voltage is 3Vm, three times higher than the supplied input voltage.
Voltage Quadruple
Adding one additional diode-capacitor stage to the voltage tripler circuit yields the voltage more quadruple.
During the First Positive Half-Cycle
The diode D1 is forward biased during the first positive half cycle of the input AC signal, but the diodes D2, D3, and D4 are reverse biased. As a result, the diode D1 permits electricity to flow through it. This current will travel to capacitor C1 and charge it to the input voltage’s peak value, Vm.
During the First Negative Half Cycle
Diode D2 is forward biased during the first negative half cycle, whereas diodes D1, D3, and D4 are reverse biased. As a result, the diode D2 permits electricity to flow through it. This current will pass to and charge the capacitor C2. The capacitor C2 is charged to double the input signal’s peak voltage (2Vm). The charge (Vm) stored in the capacitor C1 is discharged during the negative half-cycle.
The capacitor C1 voltage (Vm) and the input voltage (Vm) are thus combined to the capacitor C2, resulting in Capacitor voltage + input voltage = Vm + Vm = 2Vm. The capacitor C2 charges to 2Vm as a result.
During the Second Positive Half-Cycle
The diode D3 is forward biased during the second positive half cycle, whereas the diodes D1, D2, and D4 are reverse biased. Because the voltage at X is negative due to the charged Vm across C1, diode D1 is reverse biased, and diodes D2 and D4 are reverse biased due to their orientation. The voltage (2Vm) across capacitor C2 is discharged as a result. This charge will pass to capacitor C3, charged to the same voltage, 2Vm.
During the Second Negative Half-Cycle
Diodes D2 and D4 are forward biased during the second negative half cycle, but diodes D1 and D3 are reverse biased. The charge (2Vm) stored in the capacitor C3 is therefore discharged. This charge will pass to the C4 capacitor, charged to the same voltage (2Vm).
The output voltage is taken across the two series-connected capacitors C2 and C4, and the capacitors C2 and C4 are in series. Capacitor C2 has a voltage of 2Vm, while capacitor C4 has a value of 2Vm. As a result, the total output voltage equals the sum of capacitors C2 and C4 voltages, i.e., C2 + C4 = 2Vm + 2Vm = 4Vm.
As a result, the total output voltage obtained using the more quadruple method is 4Vm, four times the supplied input voltage.
Summary of the Voltage Multiplier
As we’ve seen, voltage multipliers are basic circuits made up of diodes and capacitors that can double, triple, or quadruple the input voltage. Also, instead of using a step-up transformer, you can apply the desired DC voltage to a given load by cascading together independent half or full-stage multipliers in series.
Depending on the output voltage ratio to the input voltage, voltage multiplier circuits are categorized as voltage doublers, more triples, quadruples, etc. Any desired voltage multiplication can theoretically be achieved, and a cascade of “N” doublers would result in an output voltage of 2N.Vp volts.
A 10-stage voltage multiplier circuit with a peak input voltage of 100 volts, for example, would provide a DC output voltage of roughly 1,000 volts or 1kV without the use of a transformer, assuming no losses.
However, because multi-stage voltage multiplication circuits can create very high voltages, the diodes and capacitors used in all multiplication circuits must have a minimum reverse breakdown voltage rating of at least twice the peak voltage across them. Furthermore, because the output voltage declines rapidly as the load current increases, voltage multipliers often give low currents to high-resistance loads.
The above Voltage Multiplication Circuits are intended to provide a positive DC output voltage. However, they may create negative voltage outputs by simply reversing the polarities of all multiplier diodes and capacitors, resulting in a negative voltage doubler.
Conclusion
To refresh our memory, a Voltage Multiplier is a diode rectifier circuit that may create an output voltage several times greater than the supplied input voltage.
Although a voltage transformer is commonly used to raise the voltage in electronic circuits, a suitable step-up transformer or a specifically insulated transformer required for high voltage applications may not always be accessible. A diode voltage multiplier circuit that boosts or “steps up” the voltage without a transformer is available.
In many aspects, voltage multipliers are similar to rectifiers in that they convert AC to DC voltages for usage in a variety of electrical and electronic circuits. Microwave ovens, powerful electric field coils for cathode-ray tubes, electrostatic and high voltage test equipment, and so on are examples of these applications. A very high DC voltage generated from a comparatively modest AC supply is required.
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