Ac Voltmeter Using Half Wave Rectifier

Full-wave rectifier is used in RF demodulator, piecewise linear function generator, AC voltmeter, watt meter and various nonlinear analog signal processing circuits. A wide-band half-wave rectifier Precision rectifier is one of important nonlinear circuits extensively used in wattmeter, AC voltmeter, RF demodulator, function fitting.

Definition: Half wave rectifier is that in which the half cycle of AC voltage gets converted into pulsating DC voltage. The remaining half cycle of AC is suppressed by rectifier circuit or the output DC current for remaining half cycle is zero.

Circuit Diagram of Half Wave Rectifier

The half wave rectifier is the simplest form of the rectifier. We use only a single diode to construct the half wave rectifier. The half wave rectifier is made up of an AC source, transformer (step-down), diode, and resistor (load). The diode is placed between the transformer and resistor (load). The half wave rectifier is the simplest form of the rectifier. We use only a single diode to construct the half wave rectifier. The half wave rectifier is made up of an AC source, transformer (step-down), diode, and resistor (load). The diode is placed between the transformer and resistor (load). Now, let's consider an average reading AC voltmeter using semiconductor diode. In this, the semiconductor diode operated for an alternate half cycle. This is because it operated on the principle of half wave rectifier. The average current through the diode can be given by the below equation. The value of 1.11 represents the form factor. In this animated lesson, students view how an oscilloscope and a DC voltmeter measure the voltage of a half-wave rectifier. Voltage Measurements of a Half-Wave Rectifier - Wisc-Online OER This website uses cookies to ensure you get the best experience on our website.

The AC input signal is first passed through transformer because the AC signal is generally supplied in high voltage because it is economical to provide AC at high voltage. The transformer present in half wave rectifier is step down transformer which converts the high voltage AC into low voltage DC.

The transformer is followed by a diode and a load resistor. The output current varies with the magnitude of the load resistor.

Working of Rectifier

When the high voltage AC passes from a step-down transformer, it gets converted into low voltage AC.

When the positive half cycle of low voltage AC passes from the diode, it makes the diode forward biased. This happens because the positive signal strikes the P-terminal of the diode and it makes the diode forward biased. Thus, when positive half of AC signal passes the diodes becomes a short circuit. Thus, the current passes through the load resistor, and the voltage drop can be seen across the load resistor.

When the negative half cycle of AC Signal passes through the step-down transformer then due to the phenomenon of mutual inductance, it converts it into low voltage AC. After that, it passes through the diode. When this negative half is passed through the diode, the p-terminal of the diode becomes negative with respect to n-terminal. Thus, the diodes become an open circuit. And the output current across the load becomes zero due to which output voltage also becomes zero.

Thus, during the positive half of AC, the output DC voltage is generated across a load and during the negative half of AC the rectifier switches to OFF state. In this way, the negative half cycle of the signal is suppressed in half way rectifier. It utilizes only half cycle of AC. Thus, it is called half-wave rectifier.

Analysis of Half-Wave Rectifier

1. Peak Inverse Voltage: The maximum voltage that the diode can bear in reverse biased mode is called its peak inverse voltage. It is a crucial factor to be considered while designing rectifier system.

1. Peak Current: The maximum current that the diode can withstand in reverse biased condition is called peak current of the diode.

1. DC Output Current and DC output voltage: The average value or DC value of the output current and DC output voltage across the load resistor can be given by the following equation below.

1. DC Output Current and DC output voltage: The average value or DC value of the output current and DC output voltage across the load resistor can be given by the following equation below.

1. Form Factor and Peak factor: The form factor of half wave rectifier is given by the ratio of RMS value of current and the average value of current.

The peak factor is defined as the ratio between the peak value of current to RMS value of current.

1. Output frequency: The output frequency of the rectifier is same as the frequency of the input signal.

f_out = f_in

1. Rectification efficiency: The rectification efficiency of the rectifier is the ratio of the DC output power to the AC input power.

The value of RF is small. Thus, it can be neglected. Therefore, the rectifcation efficiency will be 0.406. In terms of percentage, it can be written as 40.6%. Thus, 40.6% is considered as the maximum possible efficiency of half wave rectifier.

Advantages of Half Wave Rectifier

1. Economical: It is low in cost.
2. Simple Circuitry: The circuit of half wave rectifier is simple to design.

Ac Voltmeter Using Half Wave Rectifier Diagram

Disadvantages of Half Wave Rectifier

1. Low rectification Efficiency: The rectification efficiency of Half wave rectifier is quite low, i.e. 40.6%. The main reason behind this is power delivered by the circuit of half wave rectifier is only for the duration of positive half of AC cycle.
2. High Ripple factor: Ripple factor is given by the ratio of the value of AC current present in the output current of the rectifier and the output dc current of the rectifier. The ripple factor in the case of half wave rectifier is quite high which is undesirable.
3. Magnetising Current and hysteresis loss: The magnetizing current and hysteresis losses occur due to DC saturation of transformer core. Due to this magnetizing current harmonics are generated, and it is undesirable for the smooth operation of half wave rectifier.

Half Wave rectifiers convert only half wave of AC either positive or negative half into DC. If we want to convert entire cycle of AC into DC then we need Full wave rectifier.

Definition: The instrument which uses the rectifying element for measuring the voltage and current is known as the rectifying instruments. The rectifying element converts the alternating current to the direct current which indicates by the DC responsive meter. The PMMC uses as an indicating instrument.

The sensitivity of the rectifying instruments is high as compared to the moving coil and the Electrodynamometer instrument. Thereby, it uses for measuring the current and voltage. The circuit arrangement of the rectifier instrument shown in the figure below. The device uses the four diodes which act as a rectifying element.

The multiplier resistance R_s uses for limiting the value of current so that their value does not extend more than the rating of the PMMC instrument.

Rectifying Element

The rectifier element is used for the conversion of the AC to DC so that the unidirectional current flows through the PMMC instrument. The copper oxide, selenium cell, germanium and silicon diode are uses for making rectifying element.

The rectifying element offers the zero resistance when it is in forwarding bias and infinite resistance when it is in reverse biased. This property of the rectifying element use for rectification purpose.

Characteristic Curve of Rectifying Element

The characteristic curve of the rectifying circuit shown in the figure below. Ideally, the rectifying instrument does not have any voltage drops in the forward direction and no current flows in the reverse direction.But practically, this is not possible. The real characteristic curve of the rectifying element shown in the figure below.

Half Wave Rectifier Circuit

The figure below shows the half-wave rectifying circuit. The rectifying element connects in series with the voltage source, resistance multiplier and the permanent moving coil instrument. The forward resistance of the diode is neglected.

Ac Voltmeter Using Full Wave Rectifier

When the DC voltage source applies to the circuit, the I_m current flows through it. The magnitude of the current is equal to the V/(R_m+R_S). The current shows the full-scale deflection to the instrument.

The AC voltage applies to the same circuit. The rectifying element converts the AC voltage into unidirectional DC voltage. Thus, the rectified output voltage obtains through the rectify instrument. The PMMC instrument deflects through the average value of current which depends on the average voltage of the apparatus.

Average Value of Voltage The above calculation shows that the sensitivity of the instrument through AC is 0.45 times the current through the sensitivity of DC.

Full Wave Rectifier Instrument

The circuit of full wave rectifier shown in the figure below.The DC voltage applied to the circuit causes the full-scale deflection of the PMMC meter. The sinusoidal voltage applies to the meter express as
The average calculation of AC is 0.9 times with that of the DC for the same value of voltage. Or we can say that the sensitivity of the instrument along with AC is 90% with that of the DC.The sensitivity of the full wave rectifier is double to that of the half wave rectifier instrument.

Sensitivity of Rectifier Instrument

The sensitivity of the instrument shows the variation of the measured quantity from input to output. The DC sensitivity of the rectifier instrument

Final fantasy 10 official strategy guide pdf free. The sensitivity of the AC rectifier type instrument depends on the type of the rectifying element use in the circuit.

Factors Affecting the Performance of Rectifier Type Instruments

The following are the factors that affect the performance of the instrument when it is used on AC.

1. Effects of Waveform – The calibration of the rectifier instrument can be done regarding the RMS value of voltage and current. The form factor of the half wave and the full wave rectifier type instrument fixes on the calibrated scale. And if the waveform of the other form factors applies to the device, the waveform error occurs in the reading.
2. Effect of Temperature Change – The resistance of the rectifying element varies with the change in temperature. And this property of the rectifying component causes the error in the instruments.
3. Effect of Rectifying Instrument – The rectifier instrument has the property of the imperfect capacitance. It allows the high-frequency current to pass through it.
4. Decreases in Sensitivity – The sensitivity of the rectifier type instrument for AC operation is lower than that of the DC operation.

Advantages of Rectifying Instrument

The following are the advantages of the rectifiers instruments.

1. The frequency range of the instruments increases from 20HZ to high-frequency range.
2. The current operating range for such type of instrument is much lower for voltmeter as compared to the other AC instrument.
3. The instrument has uniform scales for the large range.
4. The accuracy of the instrument is ±5 percent when it is in normal operating condition.

Applications of Rectifying Instrument

The following are the applications of the rectifying instrument.

1. The instrument uses for measuring the voltage whose range lies between 50 – 250 V.
2. It use as a milliammeter or micro-ammeter.
3. The rectifying instrument use in the communication circuit for measurement.

Full Wave Rectifier

The sensitivity of the rectifying type voltmeter is less than that the sensitivity of the DC voltmeter. Thus, the loading effect of the ac rectifier voltmeter is higher than the dc voltmeter.

Ac Voltmeter Using Half Wave Rectifier