The role of rectifier circuits is to transform AC electrical energy into DC electrical energy, which is widely used in the field of electronic devices and power systems, and is one of the basic circuits in power electronics technology. Commonly used rectifier circuits are divided into the following categories.

1. Diode half-wave rectifier

Diode half-wave rectifier circuit is the basic form of rectifier circuit, its structure is simple, only through a diode to realize the rectification function, as shown in Figure 1. It uses the diode's unidirectional conductive properties, in the positive half-cycle of the AC voltage, the diode is in the forward bias state, allowing the current to flow smoothly, the output DC voltage; in the negative half-cycle of the AC voltage, the diode is reversed bias, effectively blocking the current through, the output voltage is zero at this time. Half-wave rectifier circuit is only half a cycle of the AC voltage to be utilized, the output waveform is half of the original waveform, the output voltage is about half of the peak value of the input AC voltage, its cost is very low, but the output voltage ripple is large. Therefore, it is more suitable for the rectification accuracy requirements are not high, the cost requirements are lower and the load current is smaller occasions.

Figure 1 Diode Half-Wave Rectification Topology

2. Diode full-bridge rectifier

Compared with the diode half-wave rectifier, the diode full-bridge rectifier consists of four rectifier diodes D1~D4 to form a bridge structure, as shown in Fig. 2. The receiving coil Ls receives the high-frequency alternating current, and in the positive half-cycle, the diodes D1 and D3 are positively conducting, and the diodes D2 and D4 are inversely cutting off; in the negative half-cycle, the diodes D2 and D4 are positively conducting, and the diodes D1 and D3 are inversely cutting off. Through the alternating conduction of these two pairs of diodes, the circuit is able to realize the complete rectification of the input alternating current, and a DC signal with small fluctuations can be obtained at the output. Diode bridge rectifier circuit can make full use of each half-wave of the input alternating current, has a high rectification efficiency, the output voltage is more stable, less fluctuation, the structure is relatively simple, has the advantages of easy to realize and maintain, but the diode conduction there will be a certain amount of voltage drop, the larger the current, the more obvious the problem, so it is not very suitable for the application of large output current.

3. Semi-controlled rectifier circuit

In order to reduce the diode full-bridge rectifier diode conduction voltage drop in the loss brought about by the semi-controlled rectifier came into being, its topology is shown in Figure 3. Semi-controlled rectifier circuit is the Figure 3 diode D2, D3 replaced by a controllable switching device, through the control of the control signal control to turn on or off, and the other part of the diode is naturally conduction or cutoff. Its mode of operation is similar to the diode full-bridge rectifier, efficiency compared to the diode full-bridge rectifier slightly improved, in addition to the circuit can be adjusted by adjusting the trigger signal and other parameters to control Q1, Q2 to change the size of the output DC voltage, with a certain degree of flexibility. Half-controlled rectifier circuit is usually suitable for small and medium power occasions, for the need for high-precision, high-efficiency power systems and high-power applications may not be the best choice.

4. Full-Bridge Synchronous Rectifier Circuit

The full-bridge synchronous rectifier circuit is a high-efficiency, high-frequency rectifier circuit that employs controllable switching elements instead of the conventional diode for rectification. As shown in Fig. 4, when the AC voltage is in the positive half-cycle, the two switching devices Q1 and Q3 of the upper bridge arm conduct in a certain order, and the two switching devices Q2 and Q4 of the lower bridge arm remain off. At this time, the current flows from the input to the output through the on switching devices of the upper bridge arm, realizing the unidirectional flow of current. When the input AC voltage is in the negative half-cycle, the two switching devices Q2 and Q4 of the lower bridge arm conduct in the opposite order, and the two switching devices Q1 and Q3 of the upper bridge arm are turned off, and at this time, the current flows from the input to the output through the on switching device of the lower bridge arm, which also realizes the unidirectional flow of the current, except that at this time, the direction of the current is to flow to the output through the lower bridge arm, which is the reverse of the positive half-cycle. As the synchronous rectifier using MOS tubes (metal oxide semiconductor field effect transistor) and other switching devices, its on-resistance is much smaller than the Schottky diode or ordinary PN junction diode, and therefore in the on-state voltage drop is small, thus significantly reducing the conduction loss, and improve the efficiency of the entire system. Since the switching speed of MOS tubes is faster than that of diodes, full-bridge synchronous rectifier circuits can operate at higher frequencies, thus reducing the size and weight of the filter and facilitating compact and lightweight design of the circuit.

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