Transistor Series And Shunt Voltage Regulator Pdf


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transistor series and shunt voltage regulator pdf

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The shunt regulator operates by maintaining a constant voltage across its terminals and it takes up the surplus current to maintain the voltage across the load. One of the most common examples of the shunt regulator is the simple Zener diode circuit where the Zener diode acts as the shunt element. As such the shunt voltage regulator is an essential element within linear power supply technology.

Under such conditions a Zener controlled transistor is always used for maintaining output voltage constant. Basically there are two types of Zener controlled transistor voltage regulators. They are. This circuit is called a series regulator because collector and emitter terminals of the transistor are in series with the load, as illustrated in the figure.

Transistor Series Voltage Regulator

The Web This site. In Fig. In this circuit however, they are used to provide a stable voltage reference V Z at the base of Tr1. The emitter voltage of Tr1 will be typically about 0. If the output voltage V OUT falls due to increased current demand by the load, this will cause V BE to increase and as a result, current through the transistor from collector to emitter will increase.

This will provide the extra current required by the load and thus regulate the output voltage V OUT. If V OUT tends to rise due to reduced current demand by the load, then this will reduce V BE as the emitter voltage rises and the base voltage remains stable due to D Z.

This regulating effect is due to the base potential of Tr1 being held steady by D Z so that any variation in emitter voltage caused by varying current flow causes a change in V BE , varying the conduction of the transistor Tr1, which will usually be a power transistor. This action counteracts the variation in load current.

With this simple circuit however, regulation is not perfect, and variations in output do occur for the following reasons. The amount of this fall is about 0. Since base current increases with load, the current through the zener diode D Z will decrease as more current is taken by the base of Tr1. Because the diode characteristic has a slope over its operating region as shown in Fig.

This in turn will slightly affect V BE and the output voltage. Because of reasons 1 and 2 above, any change in load will result in less than perfect regulation, therefore any change at the output will slightly change the loading on the input circuit.

As the input is normally taken from an un-regulated supply, the input voltage will be easily affected by slight changes in load current, As the input voltage is also the supply for the reference voltage V Z any change in output current, by affecting the input voltage, can produce a noticeable effect on the output voltage, slightly reducing the effectiveness of the regulation.

Each of the above effects is small, but added together they will provide an overall effect that is noticeable when the supply is operating under demanding conditions. Nevertheless this inexpensive circuit is effective enough for many applications, and is more efficient than the shunt regulator. Also, by using a suitable power transistor, the series regulator can be used for heavier load currents than the shunt design.

To improve on the simple series regulator a feedback circuit and error amplifier can be added to the basic series circuit. In this system the reference voltage V Z is compared with a feedback voltage V F , which is a portion of the actual output voltage. The difference between the two inputs produces an error voltage that is used to vary the conduction of the control element, correcting any error in the output voltage. A circuit diagram for this system is shown in Fig.

Tr1 is the series control element. It will usually be a power transistor, mounted on a substantial heat sink to cope with the necessary power dissipation. Tr2 is the error amplifier and its gain is set by the value of its load resistor R3. This will cause a change in the error voltage controlling Tr1 and a change in the output voltage V OUT.

VR1 therefore provides a variable output voltage, which, once set remains stable at that setting. This increases the collector current of Tr2 and so increases the p. If the output voltage tends to decrease, then so does V F. Tr2 conducts less and the current through R3 falls, reducing the p.

Tr1 base voltage rises, and increases the conduction of the control transistor. This will prevent damage to the supply in the event of too much current being drawn from the output, or even a complete short circuit across the output terminals.

Two components have been added, Tr3 and R5. The resistor R5 is a very low value typically less than 1 ohm. When the load current rises above a predetermined value, the small voltage developed across R5 will become sufficient at about 0.

The output current will not be allowed to increase above a predetermined amount, even if a complete short circuit occurs across the output terminals. Under these conditions the output voltage will fall to zero for as long as the excess current condition persists, but the supply will be undamaged. Where regulated supplies are used, the DC input voltage to the regulator is often considerably higher than the required output voltage. Therefore if a PSU fault occurs, it is possible that the regulated output voltage may suddenly rise to a level that can damage other components.

For this reason it is common to find over voltage protection included in stabilised supplies. The circuit shown in Fig. VR2 is a potentiometer, so that a voltage may be taken from the resistor network to correctly bias the diode D1. This diode has its cathode held at 0V by R8, and VR2 is adjusted so that D1 is just out of conduction, i.

Therefore there will be a substantial rise in the voltage at R7 slider, which will cause D1 to conduct, supplying a pulse of current to the gate of thyristor Th1, causing it to "fire" and conduct heavily until V OUT falls to practically 0v. R9 is included to limit the resulting current flow through the thyristor to a safe level. The large current that flows as Th1 fires will now cause the current limiter circuit to come into operation as previously described.

This will safely shut down the supply until the over current caused by Th1 has disappeared, which will of course happen as soon as V OUT reaches 0V, but should the over voltage still be present when Th1 switches off and V OUT rises again, the circuit will re-trigger, causing the voltage across the load to repeatedly alternate between its normal value and zero; a harmless but clear symptom of an over voltage problem. Hons All rights reserved. Revision Learn about electronics Power Supplies.

Power Supply Basics 2. Regulated Power Supplies 3. Switched Mode Power Supplies. Voltage Regulators 2. Module 2. After studying this section, you should be able to: Understand the operation of series voltage regulators.

Module 2.1

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Transistor Series Voltage Regulator

The series linear regulator provides a high level of performance, especially when low noise, ripple and transients are required in the regulated output. There is a good variety of circuits using discrete electronics components that provide linear regulation with a series pass element, and in addition to this, virtually all linear regulator ICs use this approach. This means that there are many options for series voltage regulators that are open when undertaking the electronic circuit design of a power supply. The series voltage regulator or series pass voltage regulator uses a variable element placed in series with the load.

The next and the last stage before load, in a power supply system is the Regulator part. Let us now try to understand what a regulator is and what it does. The part of electronics that deal with the control and conversion of electric power can be termed as Power Electronics.

Transistor Shunt Voltage Regulator

In a power supply system, a regulator is an essential component, used to control the output power in power electronics. The power electronics can be defined as the control as well as the conversion of electrical power in the part of electronics. A voltage regulator generates a stable output for the variations in input or load. There are different types of voltage regulators like Zener, series, shunt, fixed positive, IC, adjustable, negative, dual tracking, etc. This article discusses an overview of the transistor series voltage regulator.

The Web This site. Shunt regulators are widely used because they are cheap, effective and simple. It is unusual however, to find a shunt regulator used as the main regulating circuit in a large power supply. Shunt regulation is only really suitable, at reasonable cost, for relatively small currents and a range of fixed, usually fairly low voltages. This is due to a disadvantage of shunt regulation, which is that a regulation current flowing through the zener diode must always be flowing in addition to the load current. This is wasteful of power if large currents are involved. The basic shunt regulator circuit is shown in Fig.

Electronic Circuits - Regulators

Power Supplies

The Web This site. In Fig. In this circuit however, they are used to provide a stable voltage reference V Z at the base of Tr1. The emitter voltage of Tr1 will be typically about 0. If the output voltage V OUT falls due to increased current demand by the load, this will cause V BE to increase and as a result, current through the transistor from collector to emitter will increase. This will provide the extra current required by the load and thus regulate the output voltage V OUT.

Series Voltage Regulator: series pass regulator

Under such conditions a Zener controlled transistor is always used for maintaining output voltage constant. Basically there are two types of Zener controlled transistor voltage regulators. They are. This circuit is called a series regulator because collector and emitter terminals of the transistor are in series with the load, as illustrated in the figure.

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voltage regulators. Zener Controlled Transistor Series Voltage Regulator The image below shows the circuit diagram of a shunt voltage regulator. The circuit.

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