Analog Circuit--Miscellaneous Talk on Rectification (1)

　　Analog circuit textbooks usually talk about rectifier circuits, but they are usually very brief, only one or two pages long, and they often only talk about the most common rectifier circuits in low-power electronic equipment. Some textbooks even only talk about bridge rectification and not full-wave rectification circuits.

In fact, the rectifier circuit looks simple, but the changes and calculations inside are quite complicated.

The simplest rectifier circuit is a half-wave rectifier circuit, as shown in Figure 01. Strictly speaking, Figure 01 includes the capacitor at the rectifier output end, which is already a rectifier filter circuit.

However, this simplest half-wave rectifier circuit has some problems, and its transformer requires special design. It is probably for this reason that the fourth and fifth editions of Kang Huaguang's "Fundamentals of Electronic Technology. Analog Part" do not talk about half-wave rectifier circuits, avoiding this problem.

Regarding the operation of the half-wave rectifier transformer, we will discuss it in detail later, but we will put it aside for now.

Figure 02 is the so-called full-wave rectifier circuit, which can be seen as a combination of two half-wave rectifier circuits composed of two secondary windings of the same transformer. Windings A1 and A2 have the same number of turns and are wound on the same iron core. The polarity of the two windings is as shown in the figure. In fact, winding A1 and winding A2 are one winding, and the connection point is the center point of this winding, or called the center tap.

In the half cycle of power frequency AC, assuming that the end of the winding point is positive, winding A1 works, but winding A2 has no current flowing due to the reverse direction of diode D2, and A2 seems to not exist during this half cycle. In the second half of the cycle, the direction of the AC voltage is opposite, winding A2 works, and A1 has no current due to the reverse direction of diode D1. Therefore, windings A1 and A2 work alternately during the two half-cycles of AC. During the half-cycle, A1 and A2 work the same as half-wave rectification. So we can say that full-wave rectification is composed of two half-wave rectifications composed of two secondary windings of the same transformer.

If the two diodes of the full-wave rectifier circuit in Figure 02 are reversed, it will become the circuit in Figure 03.

The only difference between the circuit in Figure 03 and the circuit in Figure 02 is that in Figure 02 the negative end of the load ZL is connected to the center point of the secondary winding of the transformer, while in Figure 03 the positive end of the load is connected to the center point of the secondary winding of the transformer.

The rectifier circuit in Figure 02 can be called positive full-wave rectification because the negative terminal of the load is connected to the center point of the secondary winding. The rectifier circuit in Figure 03 can be called negative full-wave rectification because the positive end of the load is connected to the center point of the secondary winding.

Put the positive full-wave rectifier circuit in Figure 02 and the negative full-wave rectifier circuit in Figure 03 together, as shown in Figure 04

We find that although the rectifier circuit on the right is different, the transformers are exactly the same.

Then we cut out the left half of the transformer of the negative full-wave rectifier circuit in Figure 03:

Then paste it into the positive full-wave rectifier circuit in Figure 02, and connect the three points C, E, and D with the three points A, E, and B to form the circuit in the upper part of Figure 06. It has both positive full-wave rectification output and negative full-wave rectification output. In other words, this is a power supply with positive and negative outputs, and the positive and negative output voltages are equal.

If you look carefully at the positive and negative full-wave rectifier circuit in the upper part of Figure 06, it is exactly the same as the circuit in the lower part of Figure 06.

However, the circuit below in Figure 06 is by no means a bridge rectifier circuit, it is just similar in appearance. The circuit below Figure 06 is a combination of two full-wave rectifier circuits.

If the negative power load of the circuit below in the figure is disconnected, there will be only upward current in winding A1 and only downward current in A2. If the positive supply load is disconnected, then there will be only downward current in winding A1 and only upward current in A2. It can be seen that the rectifier circuit below Figure 06 is not a bridge rectifier circuit, but a combination of two full-wave rectifier circuits.