What Is Full-Wave Rectification?

Full-wave rectification is a circuit for AC rectification. In this rectifier circuit, current flows through one rectifier device (such as a crystal diode) during one half cycle, and current flows through the second rectifier device during the other half cycle, and the connection of the two rectifier devices enables The current flowing through them flows through the load in the same direction. The waveform before and after full-wave rectification is different from half-wave rectification. The two half-waves of AC are used in full-wave rectification. This improves the efficiency of the rectifier and makes it easy to smooth the adjusted current. Therefore, full-wave rectification is widely used in rectifiers. When applying a full-wave rectifier, its power transformer must have a center tap. Regardless of the positive half cycle or the negative half cycle, the direction of the current through the load resistor R is always the same.

Full-wave rectification is a circuit for AC rectification. In this rectifier circuit, current flows through one rectifier device (such as a crystal diode) during one half cycle, and current flows through the second rectifier device during the other half cycle, and the connection of the two rectifier devices enables The current flowing through them flows through the load in the same direction. The waveform before and after full-wave rectification is different from half-wave rectification. The two half-waves of AC are used in full-wave rectification. This improves the efficiency of the rectifier and makes it easy to smooth the adjusted current. Therefore, full-wave rectification is widely used in rectifiers. When applying a full-wave rectifier, its power transformer must have a center tap. Regardless of the positive half cycle or the negative half cycle, the direction of the current through the load resistor R is always the same.

Chinese name

Full wave rectification

Foreign name

full-wave rectification

Use

Provides rectifier efficiency

Subjects

electronic circuit

Full-wave rectification principle

Full-wave rectification makes use of both half cycles of the alternating current. Its various rectification factors are different from those of half-wave rectification. The full wave rectifier circuit is shown in the figure. It consists of a secondary power transformer Tr with a center tap, two rectifier diodes D1, D2 and a load resistor RL. The transformer secondary voltages u21 and u22 are equal in magnitude and opposite in phase, that is,

u21 =-u22 =

In the formula, U2 is the effective value of the AC voltage of the secondary half-winding of the transformer.

The working process of the full-wave rectifier circuit is: in the positive half cycle of u2 (t = 0 ~ ), D1 is forward-biased, D2 is reverse-biased, and RL has a current flowing from top to bottom. the same.

In the negative half cycle of u2 (t = ~ 2), D1 reverses and turns off, D2 forwards and turns on, and a current flows from top to bottom on RL.

The voltage on RL is the same as u22. The rectified waveform can be drawn as shown in Figure Z0704. It can be seen that a unidirectional pulsating current and a pulsating voltage are also obtained on the load RL. The average values are: GS0705

The average current flowing through the load is: GS0706

When selecting a rectifier diode, these two parameters should be used as limit parameters.

Full-wave rectification working process

The working process of the full-wave rectifier circuit is: during the positive half cycle of u2 (t = 0 ~ ), D1 is forward-biased, D2 is reverse-biased, and RL has a current flowing from top to bottom. The voltage on RL and u21 the same.

In the negative half cycle of u2 (t = ~ 2), D1 reverses and turns off, D2 forwards and turns on, and RL also has a current flowing from top to bottom. The voltage on RL is the same as u22. The rectified waveform can be drawn as shown in Figure Z0704. It can be seen that the load can also obtain a unidirectional pulsating current and pulsating voltage. The average values are:

GS0705

The average current through the load is

GS0706

The average current (ie forward current) flowing through diode D is

The highest reverse voltage across the diode is

When selecting a rectifier diode, these two parameters should be used as limit parameters.

Full-wave rectification

The DC component of the full-wave rectified output voltage (compared to half-wave) is increased, and the pulsation is reduced. However, the transformer requires a center tap, which is troublesome to manufacture. The occasion.

Full -wave rectification circuit

Double half-wave rectifier circuit

Full-wave rectifier circuit with transformer secondary center tap. It is easy to see from the circuit of FIG. 2 that it is a combination of two half-wave rectifier circuits, so it is also called a double half-wave rectifier circuit. The center tap of the transformer is the ground potential, which divides the positive and negative half cycles of the AC voltage into two parts. In the positive half cycle of the sinusoidal alternating current, the diode DA is turned on, and the current passes through DA to the load; in the negative half cycle, the diode DB is turned on, and the current passes through the DB to the load. Compared with a half-wave rectifier circuit, current flows through the load on both the positive and negative half cycles of the AC voltage. Although the current flowing to the load does not increase at each moment, the average output current is doubled than half-wave rectification, and the current flowing through each tube is 1/2 of the load current. The average output voltage under load is 0.9 times the effective value of the secondary half winding voltage of the transformer ^[1] .

Double half-wave rectifier circuit

Bridge full wave rectifier circuit

A rectifier circuit often used is a bridge full-wave rectifier circuit. Its transformer secondary has only one winding, which is connected to a bridge composed of four diodes. The four tubes are divided into two pairs, and no pair works in series. When the positive half cycle of the sinusoidal alternating current arrives, that is, when the upper end of the transformer secondary is positive, the diodes DA and DC are turned on and the diodes DB and DD are turned off, as shown in Figure 3b. When the second half of the sinusoidal AC voltage arrives, that is, when the upper end of the transformer is negative with respect to the lower end, the diodes DB and DD are turned on and the diodes DA and DC are turned off, as shown in FIG. 3c. It can be seen that whether DA and DC are on, or DB and DD are on, the direction of the current flowing through the load is the same, and the voltage generated on the load is positive, negative and negative. The output waveform is the same as the rectification waveform of a transformer with a center-tapped full-wave rectifier, as shown in Figure 3d. Each pulse waveform corresponds to two pass tubes ^[1] .

In addition, when the DA and DC tubes are turned on, they can be regarded as a short circuit. The reverse peak voltage of the transformer secondary is added to the cut-off tubes DB and DD (the two tubes are connected in parallel), so the reverse voltage experienced by each tube The peak voltage is 2Erms. The output voltage added to the resistive or inductive load is 0.9 times the secondary rms voltage of the transformer; the output voltage added to the capacitive load is 2 times the secondary rms voltage of the transformer. It is generally estimated that the output voltage is 1.2Erms with a load. The two pairs of diodes work alternately, and the output current is doubled compared to the half-wave rectifier. The current ID flowing through each tube is only half of the load current Id, that is, ID = 1 / 2Id ^[1] .

Bridge full wave rectifier circuit

Full-wave rectification three-phase full-wave rectification

Single-phase half-wave whole circuit

Single-phase half-wave resistive load rectifier circuit: Due to the unidirectional conductive characteristics of semiconductor diode D, only when the secondary voltage U2 of transformer B is a positive half cycle, current IL flows through load RL, and IL is cut off during the negative half cycle Let the voltage UL across the load be a unidirectional pulsating DC voltage, U = its DC component ^[2] .

Single-phase full-wave rectifier circuit

Single-phase full-wave capacitive load rectification circuit: The secondary winding of the power transformer B has a center tap 0; therefore, AC voltages U21 and U22 with equal voltage values and 180 ° phase differences can be obtained, and rectified by diodes D1 and D2, respectively. When the capacitor C (ie, resistive load) is not added, when the AC voltage of the secondary winding 1 of the transformer B is positive and the two terminals are negative, D1 is turned on and D2 is turned off. The current flowing through the load is ID1, and the other half During the cycle, the 2 terminal is positive and the 1 terminal is negative. At this time, D2 is turned on, D1 is turned off, and the current ID2 flowing through the load. ID1 and ID2 alternately flow through the load, so that the load current IL is a unidirectional continuous pulsating DC ^[2] .

Single-phase bridge rectifier circuit

Capacitive load single-phase bridge rectifier circuit: Its four arms are composed of four diodes. When the secondary terminal of transformer B is positive and the two terminals are negative, diodes D2 and D4 are turned on due to the forward voltage. D1 and D3 are cut off due to reverse voltage. At this time, the current from the transformer 1 terminal passes D4 through RL, and then returns to 2 terminal through D2. When terminal 1 is positive, diodes D1 and D3 are on, D2 and D4 are off, and current flows from terminal 2 to RL through D3, and then returns to terminal 1 through D1. Therefore, like full-wave rectification, current flows through the load during the positive and negative half cycles of a cycle, and it is always the same direction ^[2] .

Three-phase half-wave rectifier circuit

The rectifier transformer's secondary is connected in a star shape, and each phase is connected to a rectifier diode (or silicon rectifier). The zero point of the transformer is the "negative" pole, and the output ends of the rectifier tubes are connected to one point as the positive pole.

Three-phase full-wave rectifier circuit

Three-phase full-wave rectifier circuit: The three-phase full-wave rectifier circuit is actually composed of two sets of three-phase half-wave rectifiers connected in series. The first three-phase half-wave rectifier is composed of transformer secondary coils L1, L2, L3 and rectifier tubes D1, D2, D3, and the second three-phase half-wave rectifier is composed of L1, L2, L3 and D4, D5, D6. At the beginning, the maximum value of positive voltage with respect to 0 point is in phase c, and the maximum value of negative voltage is in phase b. The current flows from 0 to L3, D3, A +, load L, R, B-, D5, and L2, and returns to 0. If the next instant, phase a is maximum, the load current will shift from phase c to phase a. At this time, the current flows back to 0 along point 0, D1, A +, load L, R, B-, D5, and L2. point. The same can be used to analyze the working situation of the three-phase full-wave rectifier after every 60 ° ^[2] .