Full Wave Bridge Rectifier – Circuit, waveforms and working principle

Full wave bridge rectifier:

This post provides an information about full wave bridge rectifier. We will also see its working principle and advantages and disadvantages.

Full wave bridge rectifier circuit diagram
Full wave bridge rectifier circuit diagram

In full wave Bridge rectifier a transformer and four diodes are used. During the positive half cycle of secondary voltage, the diodes D2 and D4 are forward-biased, but diodes D1 and D3 do no conduct. The current is through D2, R, D4 and secondary winding.

During the negative half cycle, the diodes D1 and D3 are forward-biased, but diodes D2 and D4 do not conduct. The current is through D1, secondary winding, D3 and R.

The load current is in the same direction in both half-cycles. Therefore a unidirectional (d.c.) voltage is obtained across load resistor.

Average voltage = Vdc = 0.636 Vp = 2Vp/p

Where Vp = peak value of secondary voltage.

Since each diode conducts for only half cycle, the current rating (Io) of the diodes must be at least – half of the dc load current. i.e. 0.5 Idc.

Each diode must withstand a peak inverse voltage equal to the peak secondary voltage. PIV = Vp.

Therefore the PIV rating of the diodes must be greater than Vp. As the output is a full-wave signal, the output frequency is double the input frequency.

The maximum efficiency of bridge rectifier is 81.2%

Advantages of full wave bridge rectifier:

  • Centre tap on the secondary of the transformer is not necessary.
  • Small transformer can be used.
  • For a bridge rectifier circuit PIV per diode is one-half of the value for each diode in a full-wave rectifier.

Disadvantages of bridge wave rectifier:

  • In this type two extra diodes are used.
  • The voltage regulation is poor.

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Half Wave Rectifier – Circuit diagram and working principle

Half Wave Rectifier:

This post provides an information about half wave recifier and its working principle.

half wave rectifier
half wave rectifier

In this type only one diode is used. Generally a step-down transformer is used to provide the required secondary voltage. The transformer isolates the load from the line. This reduces the possibility of electric shock.

In the positive half cycle of secondary voltage, the diode is forward biased for voltages greater than the offset voltage. The offset voltage is 0.7 V for silicon diodes and 0.3 V for germanium diodes. This produces a half sine wave of voltage across the load resistor.

In the negative half cycle, the diode is reverse biased. The load current drops to zero.

The load current is always in the same direction. This provides rectification.

Average Voltage = Vdc = Vp/p = 0.318 Vp

Where, Vp = peak value of voltage across secondary. The value of direct current, the diode can handle is called as ‘Current rating of diode’ (Io).

Peak Inverse Voltage – In the negative half – cycle, the diode is reverse-biased. All secondary voltage appears across the diode. The maximum negative (reverse) voltage appearing across the diode is called the ‘Peak Inverse Voltage’ (PIV). To avoid break down, the PIV must be less than PIV rating of the diode. For half wave rectifier PIV = Vp.

Maximum efficiency of half wave rectifier is 40.6 %.

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Regulated Power Supply – Circuit Diagrams and Working Principle

Hello folks, today we are going to learn about the regulated power supply in details. We will try to explain:

  • Ordinary DC Power supply
  • What is the need for a Regulated Power supply
  • Working of the Regulated Power supply

Introduction to Power Supply

We all know that many electronic circuits using tubes or transistors requires a DC power supply. We cannot use DC batteries everywhere because DC batteries are costly and require replacement once discharged. So in such scenarios, we need to make use of electronic circuits which can convert ac supply into dc power supply using a rectifier-filter system, these kinds of electronic circuits are called as DC power supply.

Rectifier-filter circuit contains an ordinary dc power supply. The output of ordinary dc power supply remains steady as long as ac mains voltage or load is contrast. But in many electronics circuits it very important to keep the contact DC power supply irrespective of variant ac mains supply. There is a high possibility of circuit damage if the DC power supply is not constant. To avoid this situation, we can make use of voltage regulating devices which can keep the DC voltage at a constant level. So this combination of Voltage regulating devices with the ordinary dc power supply is called as Regulated DC power supply. Regulated DC power supply is an electrical device which produces the constant DC power supply irrespective of variant ac mains supply.

Ordinary DC Power Supply

Below circuit shows ordinary or unregulated power supply. This circuit contains a rectifier and a filter circuit. The output of a rectifier is pulsating dc because of the presence of pulsating ac component. The filter circuit is used to remove these pulsations of AC component to produce a steady dc output.

Unregulated DC power supply
Unregulated DC power supply

Limitations of Ordinary DC power supply

  1. DC output voltage is directly proportional to the AC input voltage. If AC voltage is increased, the output will increase in the same proportion, thus we won’t get constant dc output voltage.
  2. DC output voltage decreases as the load current increases because of voltage drop in transformer windings, filter and rectifier circuit.

What is the need for a Regulated Power supply?

We have already covered the limitations of an ordinary power supply. In an ordinary power supply, the voltage regulation is poor i.e. d.c. output voltage changes considerably with load current. Moreover, output voltage also changes due to variations in the input a.c. voltage. Thus there is a need of regulated power supply.

Working of the Regulated Power supply

The general block diagram of regulated power supply is shown below:

Regulated Power Supply Block Diagram
Regulated Power Supply Block Diagram

Construction and working of regulated power supply

1. AC supply and transformer:

A power supply is used to provide the required amount of power at specific voltage from a primary source which can be ac mains or a battery. A transformer changes the ac mains (line) voltage to a required value and it is used to step the voltage up or down. In a transistor radio it may be a step-down transformer and in a CRT it may be a step-up transformer. Transformer provides isolation from the power line. It should be used even when any change in voltage is not necessary.

2. Rectifier:

Full wave bridge rectifier circuit diagram
Full wave bridge rectifier circuit diagram

A rectifier converts ac into dc. It may be a half-wave rectifier, a full-wave rectifier using a transformer with centre-tapped secondary winding or a bridge rectifier. But the output of a rectifier may be fluctuating.

3. Filter:

LC filter
LC filter

A filter circuit is used for smoothing out the ac variations from the rectified voltage. There are four types of filters: 1) Capacitor filter, 2) Inductor filter, 3) L-C filter and 4) R-C filter.

4. Voltage regulator:

A voltage regulator is necessary to maintain a constant output dc voltage by providing line regulation and load regulation. For this purpose, we can user A Zener-regulator, transistorized regulator or three terminal IC regulator. A switched mode power supply (SMPS) is used to provide large load current with negligible power dissipation in the series pass transistor.

We recommend you to please watch below lecture for a complete understanding of Regulated Power Supply:

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