Voltage multiplier used as Voltage Tripler and Quadruples

The half-wave voltage doubler, shown in the earlier figure can be extended to provide any multiple of the peak input voltage (that is, 3 V_{s max}, 4 V_{s max} or 5 V_{s max}), as illustrated in the figure shown below. It is obvious from the pattern of the circuit connections how additional diodes and capacitors are to be connected to provide output voltage, 5,6,7 or 8 times the peak input voltage from a supply transformer of rating only V_{s max}, and each diode in the circuit of PIV rating 2 V_{s max}. If load is small and the capacitors have little leakage, extremely high dc voltages can be obtained from such a circuit using many sections to step-up the dc voltage.

In operation capacitor C₁ is charged through diode D_l to a peak value of transformer secondary voltage, V_{s max} during first positive half-cycle of the ac input voltage. During the negative half cycle capacitor C₂ is charged to twice the peak voltage 2 V_s developed by the sum of voltages across capacitor C₁ and the transformer secondary. During the second positive half-cycle, diode D₃ conducts and the voltage across capacitor C₂ charges the capacitor C₃ to the same 2 V_{g max} peak voltage. During the negative half-cycle diodes D₂ and D₄ conduct allowing capacitor C₃ to charge capacitor C₄ to peak voltage 2 V_{S max}. From the fogure shown below it is obvious that the voltage across capacitor C₂ is 2 V_{s max}, across capacitors C₁ and C₃ it is 3 V_{s max} and across capacitors C₂ and C₄ it is 4 V_{s max}.

If additional diodes (each diode of PIV rating 2 V_{s max}) and capacitors (each capacitor of voltage rating 2 V_{s max}) are used, each capacitor will be charged to 2 V_{s max}. Measuring from the top of the transformer secondary winding (figure below) will give odd multiples of V_{g max} at the output, while measuring from the bottom of transformer secondary winding will give even multiples of the peak voltage, V_{s max}.

Some electronic devices, such as cathode ray tubes (in picture tubes in TV receivers, oscilloscopes and computer display) need dc power supply at high voltage with low current. This requirement can be met with either by employing a step-up transformer with a rectifier circuit or by employing voltage multiplier. Since transformers are very bulky and costly, voltage multipliers are preferred. By using voltage multipliers, the voltage level is usually raised well into the hundreds or thousands of volts.

Generally such circuits are employed when both the supply voltage and load are maintained constant.

Introduction to full-wave voltage doubler

Full-Wave Voltage Doubler

The circuit diagram for a full-wave voltage doubler is given in the figure shown below. During the positive cycle of the ac input voltage, diode D₁ gets forward biased and so conducts charging the capacitor C₁ to a peak voltage V_smax with polarity indicated in the figure, while diode D₂ is reverse-biased and does not conduct.During the negative half-cycle, diode D₂ being forward biased conducts and charges the capacitor C₂ with polarity shown in the figure while diode D₁ does not conduct. With no load connected to the output terminals, the output voltage will be equal to sum of voltages across capacitors C₁ and C₂ that is, V_C1 + V_C2 or (V_{s max} + V_{s max}) or 2 V_{s max}. When the load is connected to the output terminals, the output voltage V_L will be somewhat less than 2 V_{s max}. The input voltage and output voltage waveforms are also shown in the figure below.

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Explanation for Half wave voltage doubler

at delivers a dc voltage twice or rnore times of the peak value (amplitude) of the input ac voltage. Such power supplies are used for high-voltage and low-current devices such as cathode-ray tubes (the picture tubes in TV receivers, oscilloscopes and computer display). Here we will consider half-wave voltage doubler, full-wave voltage doubler and voltage tripler and quadrupler.

Half-Wave Voltage Doubler

The circuit of a half-wave voltage doubler is given in figure shown below. During the positive half cycle of the ac input, voltage, diode D₁ being forward biased conducts (diode D₂ does not con­duct because it is reverse-biased) and charges capacitor C₁ upto peak values of secondary voltage V_smax with the polar­ity, as marked in figure shown below.

During the negative half-cycle of the input voltage diode D₂ gets forward biased and conducts charging capacitor C₂. For the negative half cycle, the lower end of the transformer secondary is positive while upper end is negative. The polarity of the capacitor C­₂ has also been marked in the figure. Now starting from the bottom of the transformer secondary and moving clockwise and applying Kirchhoffs voltage law to the outer loop we have

-V_smax – V_c1 + V_c2 = 0

Or

V_c2 = V_smax + V_c1= Vsmax + Vsmax = 2V_smax = Twice the peak value of the transformer secondary voltage. (Since V_c1 = V_smax)

During the next positive half-.cycle diode D₂ is reverse-biased and so acts as an open and capacitor C₂ discharges through the load If there is no load across the capacitor, C₂ both capacitors stay charged – C₁ to V_smax and C₂ to 2V_smax. If, as expected there is a load connected to the output terminals of the voltage doubler, the capacitor C₂ discharges a little bit and consequently the voltage across capacitor C₂ drops slightly. The capacitor C₂ gets recharged again in the next half-cycle. The ripple frequency in this case will be the signal frequency (that is, 50 Hz for supply mains.

adapter circuit that can deliver up to 3A at 12V output voltage

This adapter circuit can deliver up to 3A at 12V output voltage. The circuit can be employed on occasions when a current of more that 3A is demanded for regulator. IC regulators of such high current rating are pretty hard to find.

The transformer T1 steps down mains voltage, to 12rms & the rectifier bridge D1 rectifies it to produce a DC voltage. The C1 filters the rectifier output and produces a DC level. The series pass transistor Q1 (2N 3055) is biased by resistor R1 (680Ω). Since zener diode D1 is under breakdown region the voltage across it will be 12V. So the total output voltage will be steady 12.7 V(theoretically). That is the zener voltage plus base emitter voltage of Q1.Here transistor Q1 will conduct the excess current required .

Skema rangkaian adaptor 12 volt 2N3055

Notes.

• If 12V zener is not available ,use the nearest value.
• The transformer T1 can be as 23oV primary;15V/5A secondary step down transformer.
• The capacitors must be rated at least 25V.
• By changing the value of the Zener diode, different output voltages can be obtained from the circuit.

The 2N3055 is a silicon Epitaxial-Base Planar NPN transistor mounted in Jedec TO-3 metal
case. It is intended for power switching circuits, series and shunt regulators, output stages and high fidelity amplifiers.

Maximum Ratings

• Collector-Base Voltage 100 V
• Collector-Emitter Voltage (RBE £ 100W) 70 V
• Collector-Emitter Voltage (IB = 0) 60 V
• Emitter-Base Voltage (IC = 0) 7 V
• Collector Current 15 A
• Base Current 7 A
• Total Dissipation at Tc £ 25 oC 115 W
• Storage Temperature -65 to 200 oC
• Operating Junction Temperature 200 oC

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Voltage Reference using LM334

This Voltage Reference Circuit. It used LM334 (ADJUSTABLE CURRENT SOURCES IC)
By fix the trend is stable. It make the pressure that pay to come out have tall stability. By can fine decorate VR1 10K Adjust Voltage Output. And You can use Voltage Input power supply at +2.5V to +20V. cause be high class voltage Output be valuable 0.8-5.0V depend on fining decorates VR1 there.

Bias Current and Offset Voltage Compensation

– Up until now we have mostly considered ideal op-amps in our discussion.

– We must, however, introduce some non-ideal characteristics, since they will have an effect on the op-amp operation.

– Transistors within the op-amp must be biased so that they have the correct values of base and collector currents and collector-to-emitter voltages.

– Ideal op-amp has no input current at its terminals.

– In practice, op-amps have small input bias currents (in the nA range).

– There is also a small offset voltage between the inputs.

Effect of an Input Bias Current

– Consider the inverting amplifier circuit shown below.

– If the input voltage is zero, there should be zero current coming into the inverting input of the op-amp.

– However, there is a small bias current, I₁, that goes through R_f.

– This current creates a voltage at the output equal to I₁R_f.

– This is the error voltage.

– The same voltage will be seen at the output of a noninverting amplifier.

– If we look at the voltage follower circuit shown below, it is easy to see that the output error voltage is –I₁R_s.

Bias current compensation in a voltage-follower

– Somehow we need to compensate for the error voltage due to the bias currents.

– In a voltage follower it is enough to add a resistor, R_f, equal to the source resistance, R_s, in the feedback path.

– The voltage drop created by I₁across the added resistor subtracts from the –I₂R₂ output error voltage.

– If I₁ = I₂, then the output voltage is zero.

– Usually they are not equal, but even then the output voltage error is reduced, since the input offset current, I_OS, is less than I₂:

V­_OUT(error) = |I₁ – I₂|R_s = I_OSR_s

Bias current compensation in other op-amp configurations

– In a noninverting amplifier we add a resistor R_c.

– The compensating resistor value equals the parallel combination of R_i and R_­f.

– The input creates a voltage drop across R_c that offsets the voltage across the combination or R_f and R_i.

– Thus, the output is reduced.

– The same is done for the inverting amplifier.

Input offset voltage compensation

– The output voltage of an op-amp when the differential input is zero should be also zero.

– However, due to unavoidable internal imbalances and due to non-zero bias currents, a small voltage, V_IO, is seen between the terminals.

– ICs provide a means to compensate for this.

– This is generally done by connecting an external potentiometer to pins designated with Offset Null.

– With zero input voltage, the output is set to zero by adjusting the potentiometer.

– The pinout for the 741 op-amp (the most common op-amp IC) is shown next.

Voltage Multipliers

Voltage multipliers

– Voltage multipliers use clamping action to increase peak rectified voltages without increasing input transformer’s rating.

– Multiplication factors of 2, 3, and 4 are common.

– They are used in high-voltage, low-current applications.

i) Voltage doubler.

– There are two types of voltage doublers:

a) Half-wave doubler.

– During the positive half-cycle of the secondary voltage, diode D₁ is forward-biased and D₂ is reverse-biased.

– Capacitor C₁ is charged to the peak of the secondary voltage (V_p) less diode drop

– During the negative half-cycle, diode D₂ is forward-biased and D₁ is reverse-biased.

– C₁ cannot discharge.

– Thus, C₁’s voltage adds to the secondary voltage to charge C₂ to approximately 2V_p.

– Under no-load conditions, C₂ remains charged.

– If load is added, C₂ will discharge through load on the next positive half-cycle only to be recharged in the following negative half-cycle.

– Resulting wave is a half-wave, capacitor-filtered voltage.

– PIV across each diode is 2V_P.

b) Full-wave doubler.

– When secondary is positive, D­₁ is forward biased and C₁ charges to approximately V_p.

– During the negative half-cycle, D₂ is forward biased and C₂ charges to approximatetly V_­p.

- Output voltage is taken across the two capacitors in series.

ii) Voltage tripler

- Exactly like the half-wave doubler, but another diode-capacitor pair is added.