Full Wave Rectifier - Definition, Working, FAQs

Half wave and full wave rectifier

Full wave rectifier:- In a full wave rectifier uni-directional, the pulsating output current is obtained for both halves of AC input voltage. It requires two junction diodes such that one diode rectifies one half and the second diode rectifies the second half of the input.

The full-wave rectifier circuit diagram is shown in fig a and the input and output waves form in fig b. The a.c. input voltage is applied across the primary P1 P2 of the transformer. The terminals S1 and S2 of the secondary are connected to the p-type crystals of the junction diodes D1 and D2 whose n-type crystals are connected to each other. A load resistance RL is connected across the n-type crystals and the central-tap T of the secondary S1S2. Full wave rectifier is centered on a Tapped rectifier.

Key Points:-

• Full wave rectifier
• Half wave rectifier
• Bridge rectification
• Bridge full wave rectifier
• Centered tapped rectifier
• Full wave rectifier circuit
• Full wave rectifier diagram
• Half wave rectifier circuit diagram
• Bridge rectifier circuit
• bridge rectifier circuit diagram
• working of full wave rectifier
• working of half wave rectifier
• Rectifier circuit diagram

Working of full wave rectifier:- Full wave rectifier circuit diagram is given below.

During the first half cycle of the a.c. the input voltage, the terminal S1 is supposed to be positive relative to T, and S2 is negative. In this situation, the junction diode D1 is forward-biased and D2 is reverse-biased. So D1 conducts while D2 does not. The current flows through diode D1, load RL, and the upper half of the secondary windings, as shown by the solid arrows in the figure. During the second half cycle of the input voltage, S1 is negative relative to T and S2 is positive. Now, D1 is reversed-biased and does not conduct, while D2 is forward-biased and conducts. The current now flows through D2, load RL, and the lower half of the secondary, as shown by dotted arrows. Thus, the diodes D1 and D2 conduct alternatively, and the current in the load RL flows in the same direction for both half cycles of the input voltage. Consequently, the output current is a continuous series of unidirectional pulses.

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Types of full wave rectifier

• Centered- tapped rectifier
• Bridge full wave rectifier

Half wave rectifier:- If we applied a.c. the voltage across a junction diode, a current start flows through the diode during the positive half cycles of the voltage. Thus, a single junction diode becomes a half-wave rectifier.

The circuit of the half-wave rectifier is shown in fig. In the half-wave rectifier diagram, the input and output waves form in fig. We applied a.c. input voltage across the primary P1P2 of a transformer. S1S2 is the secondary coil of the transformer. One terminal S1 of the secondary coil is connected to the p-type crystal of the junction diode, and the other terminal S2 is connected to the n-type crystal through a load resistance RL.

Working of half-wave rectifier:-Consider the half wave rectifier diagram/circuit of half wave rectifier. During the first half cycle of the AC input when the terminal S1 of the secondary is supposed positive and S2 is negative, the junction diode is forward biased. Hence current flows through the load RL in the direction shown by arrows. The current produces across the load and output voltage of the same shape as the half cycle of the input voltage. During the second half cycle of the AC input, The terminal S1 is negative, and S2 is positive the diode is now reverse biased. Hence there is almost zero current and zero output voltage across R. The process is repeated.

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Thus, the output current is unidirectional but intermittent and pulsating as shown in the lower part of the figure.

Since the output current corresponds to one half of the input voltage wave the other half is missing the process is called half-wave rectification. The transformer supplies the necessary voltage to the rectifier. If direct current at a high voltage is to be obtained from the rectifier is it necessary for power supply, then a step-up transformer is used as shown in the figure. In this case, a step-down transformer is used in the rectifier.
In the above, we discuss the half-wave rectifier and full-wave rectifier. Now, we discuss the bridge rectifier.

Bridge rectification

Full bridge rectifier:- An important factor for fire circuit arrangement is the bridge rectifier or double wave rectifier shown in the figure. It is known so because in this circuit the four PN junction diodes D1 D2 D3 and D4 are arranged in the form of resistance of the Wheatstone bridge network. The two opposite ends A and C of the network are connected to the ends S1 and S2 of the secondary of the transformer while the ends b and d are connected to the load resistance RL. The full-wave bridge rectifier diagram is shown in fig.

Working of the bridge wave rectifier:- Under the action of an AC voltage applied to the primary of the transformer the voltage across the secondary is given by

E₁ = E₀sin ⍵t

Which varies with ⍵t as shown in the figure.

In the half-cycle in which the potential of the transformer has a full polarity such that A is positive and C is negative, diodes D1 and D3 are forward biased and conduction takes place via diode D1, load resistance R, and diode D3. Consequently, a current I1 flows in the direction A B R D C S2 S1 A as shown in the figure. On the other half cycle when the terminal C is positive with respect to A diodes D2 and D4 are forward biased whereas diodes D1 and D3 are reverse biased. Therefore conduction takes place via the diode D2 and t4 and a current I flows in the direction C B R D A S1 S2 C. Same process is repeated in the subsequent half cycle of the AC input. However, the current through the load R flows in the same direction in both the halves of the applied AC voltage. Thus the current is unidirectional, and the wave shape of the current in the load is similar to that of a full-wave rectifier, shown in the figure.

Full-wave rectifier with capacitor filter and half-wave rectifier with capacitor filter

To decrease the ripple content in the output, various types of filter circuits are used.

The simplest type of smoothing circuit is a shunt capacitor filter obtained by placing a capacitor c in parallel with the load resistance R as shown in the figure. It is an effective way of smoothing or filtering the AC components from the output of the rectifier. The capacitor C is so chosen so that its reactance (1/⍵C) at the frequency of AC mains is very small as compared to the load R. Then the AC component finds a low reactance shunt path through the capacitor and are mostly bypassed. Thus, the AC components or ripple flowing through the load decrease, or in other words, ripples are filtered from the output voltage. The pulsating output voltage of the rectifier, in the absence of capacitor C, is shown in the figure. (a) while the filtering action of the capacitor is indicated in figure(b).

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The capacitor C connected in parallel to the load resistance R appreciably modifies the operating condition of the rectifier. When the output voltage of The rectifier increases, the capacitor C charges up almost equal to the peak voltage E0 of the rectified output at the end of the first quarter cycle (point p )and stores energy in its electrostatic field. During the subsequent half-cycle, when the rectified output drops to zero and then rises again the capacitor C discharge exponentially through R in figure(b), delivers its stored energy to the load, and maintains a voltage across it at a higher value in comparison with the case of rectifier using no capacitor. At Q, the capacitor begins to the peak potential of the rectified output at L and is then discharged again to the point M. This cycle is repeated again and again. It may be seen that the voltage across the capacitor varies in the manner shown by the solid curve PQLMN of figure(b), the variation is much less than in the rectifier output. The extent of this varies depending on the time constant CR of the capacitor-load circuit. If the time constant CR is large in comparison with the time period of the applied AC, the capacitor discharges quite slowly, the fall in voltage of the load is small and the DC output voltage remains nearly constant.

It may be seen that the diode current does not flow during the whole positive half cycles but flows in the short pulses e.g., from ⍵t = θ₁ to ⍵t = θ₂. The phase angle θ₁ at which the diode is charged conducting is called cut in point and the phase angle θ₂ at which stops conducting is called cutout point; the interval θ₂ - θ₁ is called charging interval.

• a single-phase full wave rectifier is a
• Single-pulse rectifier
• Multiple pulses rectifier
• Two pulse rectifier
• Three pulse rectifier

A single-phase full-wave rectifier is a single pulse rectifier.

Single-phase half wave controlled rectifier

A Single Phase Half Wave Controlled Rectifier circuit consists of SCR (silicon controlled rectifier), a.c. voltage source and load R. A circuit diagram of the Single Phase Half Wave Controlled Rectifier is shown in the figure.\

Single-phase full wave rectifier controlled rectifier with RL load

Single-phase full wave rectifier with RL load is shown in fig.

The single-phase fully controlled rectifier converts the single-phase a.c. into d.c. It is used in some applications like battery charging, speed control of DC motors, and the front end of UPS.

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