CN207664888U - High efficiency full bridge rectifier - Google Patents

Abstract

The utility model provides a high-efficiency full-bridge rectifier circuit for low-frequency sinusoidal alternating current. The circuit is composed of four power field effect tubes to form a full-bridge rectifier, and two low-side field effect tubes are controlled by two photoelectric couplers. The switching action corresponds to the opening and closing of the positive and negative half cycles of the sinusoidal alternating current; the switching action of the two high-side FETs is managed by a high-speed voltage comparator, and the voltage polarity information at both ends of the high-side FETs is fed back to the input of the voltage comparator terminal, so that the high-side field effect transistor has the unidirectional conduction characteristics of the diode. The advantage of the utility model is that in the working environment of low voltage and high current, the rectification efficiency can be increased by 10%-15% compared with the common diode rectification circuit.

Description

High efficiency full bridge rectifier circuit

technical field

The content related to the high-efficiency full-bridge rectifier circuit of the utility model belongs to the field of electronic technology, and is used for AC-DC conversion of power supply.

Background technique

The function of the rectifier circuit is to convert the AC voltage into a DC voltage, and a bridge rectifier circuit structure composed of four diodes is generally used. However, in the process of low voltage and high current rectification, the voltage drop of the rectifier diode cannot be ignored. The tube voltage drop is generally 1.0V-2.0V, and the power loss generated by the rectifier diode accounts for a large proportion, usually reaching 10% of the total power. -20%. Therefore, the diode bridge rectifier circuit in a low-voltage environment has the disadvantage of low working efficiency, which is a major damage to the effective use of electric energy.

In order to reduce the power loss of the rectifier circuit, a power field effect transistor is currently used to replace the diode to undertake the rectification work. The on-resistance of the low withstand voltage power field effect transistor is very small, usually around 10mΩ. Even if a current of 10A flows, the voltage drop generated is far lower than that of ordinary diodes, thus greatly reducing the rectification device itself. power loss. However, the diode is a simple unidirectional conduction device without external control; while the field effect transistor is a controlled device, which must be controlled synchronously according to the needs of on and off. In order to make the FET achieve the goal of unidirectional conduction, the industry has introduced a synchronous rectification circuit based on the power FET. With the protection diode inside the power FET as a reference, when the voltage in the positive direction is applied to the FET, the other One synchronous control voltage turns on the FET, and when a voltage in the opposite direction is applied to the FET, the synchronous control voltage turns off the FET. At present, synchronous rectification circuits are basically used in high-frequency switching circuits, and a full-wave synchronous rectification structure with double windings is used, as shown in Figure 4. In the low-frequency sinusoidal AC environment, due to the continuous change of the input voltage amplitude, there is no fixed switching time between on and off, and it is not easy to obtain a synchronous signal. Basically, no synchronous rectification method is used, and the classic diode rectification circuit is generally used.

The basic requirement for the power field effect tube to replace the diode to undertake the rectification work is unidirectional conduction, that is, with the protection diode inside the power field effect tube as a reference, it is turned on when a positive voltage is applied to both ends, and it is turned off when a reverse voltage is applied to both ends. In a low-speed environment, it is only necessary to detect the voltage difference between the source and drain of the field effect tube, quickly feed back to the gate of the field effect tube, and complete the adjustment of on and off, without the need for external synchronization signals to participate in the control. Electronic technology can fully realize this control goal. Accordingly, the utility model designs a high-efficiency full-bridge rectification circuit structure based on power field effect transistors, which can realize high-efficiency rectification work in a low-frequency sinusoidal alternating current environment.

Contents of the invention

The purpose of this utility model is to provide a high-efficiency full-bridge rectifier circuit for low-frequency sinusoidal alternating current. From a technical point of view, it has the following characteristics:

The high-efficiency full-bridge rectifier circuit consists of four power FETs to form a full-bridge circuit. The connection relationship between the four power FETs is based on the principle that the polarity of the internal protection diodes of the power FETs is consistent with that of the diodes in the ordinary rectifier bridge, that is, the power field The effect transistor is in the reverse conduction mode, as shown in Figure 1; the gate and source electrodes of the two low-side power field effect transistors Q2 and Q4 are respectively connected to the output port of the optocoupler with respect to the negative electrode of the rectified output voltage, and the two high-side power Field effect transistors Q1 and Q3 respectively form an analog diode circuit with a voltage polarity discrimination drive circuit, as shown in Figure 3; the input terminals of the two photocouplers are connected in series with a current-limiting resistor to the sinusoidal AC circuit before rectification, and the full bridge The input port of the rectifier circuit is connected to the sinusoidal AC circuit before rectification after the inductor L1 is connected in series, the output port of the full bridge rectifier circuit is connected to the filter capacitor, and the circuit has no external control terminal.

The analog diode circuit is composed of diode D5, high-speed voltage comparator IC3, field effect transistor Q1, resistors R9, R10, R5, R1 and capacitor C7, wherein diode D5 cathode, high-speed voltage comparator non-inverting terminal and power supply negative terminal, field The sources of the effect transistor Q1 are connected to each other to form a collinear line, the drain of the field effect transistor is connected to the inverting terminal of the voltage comparator through the resistor R9, and the pull-up resistor R10 is connected to the positive terminal of the power supply and the output terminal of the high-speed voltage comparator. The operating voltage is supplied externally, as shown in Figure 2.

The beneficial effects of the high-efficiency full-bridge rectifier circuit compared to the diode rectifier circuit:

In the working environment of low voltage and high current, compared with ordinary diode rectification circuit, the rectification efficiency can be increased by 10%-15%.

In the rectification process of the full-bridge rectifier circuit, in the bridge composed of four power FETs, the two FETs on the opposite side are always turned on at the same time, and the two FETs on the other side are cut off at the same time, such as Q1 and Q4 When it is turned on, Q3 and Q2 are cut off at the same time. Taking the negative terminal of the output voltage as a reference, there are two low-side rectifiers and two high-side rectifiers, as shown in Figure 1. Q1 and Q3 are high-side FETs, and Q2 and Q4 are low-side FETs. As long as the two low-side rectifiers are not turned on at the same time, that is, Q2 and Q4 can be turned off at the same time, but they cannot be turned on at the same time, and the two high-side rectifiers not only cannot be turned on at the same time, but must also have diode conduction characteristics. The polarity of the voltage at the terminal determines its on and off states. For a rectifier bridge with a filter capacitor connected to the output, the output voltage is maintained at a higher voltage amplitude, and within one cycle of the sinusoidal AC, there is a time when the input voltage will be lower than the output voltage. Only when the input voltage is higher than the output voltage, can the high-side field effect transistor Q1 or Q3 be turned on, and this working characteristic can be called the voltage follow-up characteristic. Designing the high-side field effect transistor of the rectifier circuit as an analog diode structure, as shown in Figure 2, has the voltage-variable characteristic. The circuit shown in Figure 2 can also be called an active diode.

The field effect transistor analog diode circuit has the ability to automatically shut down the reverse voltage and has a high voltage polarity discrimination sensitivity. In Fig. 2, the diode D5 is used to limit the highest potential of the input terminal of the voltage comparator, and the lowest negative potential of the input terminal is clamped by the internal protection diode of the field effect transistor Q1. The voltage comparison chip adopts LM397, and its level transmission delay time is about 0.3μs, which is much smaller than the commonly used voltage comparator LM393 transmission delay time. The output terminal of the voltage comparator LM397 has an OC structure inside, and only needs to add a pull-up resistor R10 to complete the pulse voltage output to drive the field effect transistor Q1. There are also some voltage comparators that use totem pole structure output, but the working voltage is generally below 5V, which cannot be used here. Although operational amplifiers such as LM358 have a totem pole structure output, when they work in a voltage comparison state, the delay time can be as long as 0.5ms, and they cannot be used.

There is a short delay effect when the diode turns from conduction to cutoff, and there is a longer delay time when the analog diode turns from conduction to cutoff, resulting in a short-term discharge current. Therefore, a pulse current suppression inductor L1 is added to the input end of the rectifier circuit to suppress the discharge current caused by the delayed shutdown. The working voltage value required by the analog diode circuit depends on the turn-on voltage requirements of the field effect tube. For NTD50N03, AON6504 and other field effect tubes, the turn-on voltage is as low as 1.7V, and the working voltage is taken as 6-10V.

The use of photocouplers to drive low-side field effect transistors is designed to simplify the circuit. The photocoupler does not need an additional working power supply, and directly drives the corresponding field effect transistor according to the polarity of the input AC voltage, and the circuit structure is simple. Although the photocoupler has a conduction gate voltage, the output voltage is maintained at a relatively high voltage amplitude during the actual rectification process with the post-stage filter capacitor. In a cycle of sinusoidal AC, the input voltage will be lower than the output voltage most of the time. Voltage, there is no rectification current near AC zero voltage, and there is no requirement to turn on the field effect transistor near AC zero voltage. Therefore, the optocoupler is fully capable of driving the field effect tube.

A complete high-efficiency full-bridge rectifier circuit is shown in Figure 3. When the input ACV1 is positive and ACV2 is negative, the field effect transistor Q1 is turned on, and at the same time, the optocoupler IC6 outputs current, and the field effect transistor Q4 is turned on to provide a low-impedance rectification path, and the rectified current passes through the inductor L1, the field effect transistor Q1, and the output DC load , Field effect transistor Q4 forms a loop; when the input ACV1 is negative and ACV2 is positive, the field effect transistor Q3 is turned on, and at the same time, the optocoupler IC5 outputs current, and the field effect transistor Q2 is turned on, providing a low-resistance rectification path, and the rectified current passes through the field effect transistor Q3, the output DC load, field effect transistor Q2, and inductor L1 form a loop; when the input AC voltage is low, the two optocouplers have no output current, and the field effect transistors Q2 and Q4 are both turned off. At this time, the rectifier bridge has no rectification current. There is also no need to provide a low resistance current path.

Description of drawings

Accompanying drawing 1 is the main structure of the full-bridge rectifier circuit constructed by four power FETs.

In the figure, ACV1 and ACV2 are the two input terminals of the AC voltage, and DCOUT+ and DCOUT- are the two output terminals of the rectified DC voltage.

Accompanying drawing 2 is the analog diode circuit based on field effect transistor.

In the figure, IC3 is a high-speed voltage comparator, and Q1 is a field effect transistor used for rectification.

Accompanying drawing 3 is a complete schematic diagram of a high-efficiency full-bridge rectifier circuit.

In the figure, ACV1 and ACV2 are the two input terminals of the AC voltage, DCOUT+ and DCOUT- are the two output terminals of the rectified DC voltage, IC5 and IC6 are photocouplers, and IC3 and IC4 are high-speed voltage comparators.

Accompanying drawing 4 is the basic structure of the dual-winding full-wave synchronous rectification circuit of the high-frequency switch circuit.

In the figure, T1 is a switching transformer, input AC pulse voltage, Q1 and Q2 are rectifier tubes, L1 is a filter inductor, DCOUT+ and DCOUT- are two output terminals of rectified DC voltage, DCOUT- is a reference ground terminal, va and vb are Two pulse voltages of the same frequency.

Detailed ways

Below in conjunction with accompanying drawing of the utility model, the implementation of the utility model is further described.

The power supply of the active diode circuit can be taken from the rectified DC voltage. When the rectified output voltage is higher than 15V, the switch step-down method can be used to reduce the power consumption of the power supply circuit; when the rectified output voltage is lower than 18V, the stable voltage can be used. The voltage diode is connected in parallel to reduce the voltage, so as to simplify the circuit structure.

In the high-efficiency rectifier circuit shown in Figure 3, the high-side uses an analog diode structure and the low-side uses a photoelectric coupler to drive the FET, just to simplify the circuit structure. The speed will be even faster. It is also because there is no dedicated drive chip for field effect tubes with high sensitive voltage comparison available, and the complex circuit structure shown in Figure 2 is adopted. If part of the circuit in Figure 2 except the power field effect transistor can be made into a dedicated drive chip, the structure of the actual rectification circuit can be greatly simplified. This dedicated driver chip should guarantee four basic requirements: high enough voltage discrimination sensitivity, fast enough signal transmission speed, large enough output current capability, and can work normally within the voltage range of 4-10V.

The inductance L1 is used to suppress the reverse discharge current caused by the delayed turn-off effect of the active diode, and the inductance can be tens of microhenries. Resistor R8 is an input current sampling resistor, which is used to detect the magnitude of the input current. The resistance value is controlled to be below 0.1Ω to reduce power loss. It can be replaced by a wire when no detection is required.

The structure of the high-efficiency full-bridge rectifier circuit is relatively independent, and it should be designed as a rectifier module to facilitate its application. The selection of field effect transistors Q1~Q4 depends on the needs of the working voltage and current. The drain-source withstand voltage should be greater than the maximum input voltage. When the peak voltage is below 50V, field effect transistors such as AOD2610, IRFZ44N, and IRF3205 can be selected.

This high-efficiency rectifier circuit is generally used for AC rectification below 50V. As the AC voltage rises, the proportion of diode voltage drop relative to the input voltage decreases, and its work efficiency improvement ratio will decrease. The test of the sample circuit shows that in the rectification of the AC 15V voltage and 2A current, the rectification efficiency can reach 96%, which is 10% higher than that of the ordinary diode bridge rectification circuit.

Claims (2)

1. High-efficiency full-bridge rectifier circuit, its structural features are: the circuit is composed of four power FETs to form a full-bridge circuit, and the connection relationship of the four power FETs is based on the protection diode inside the power FET and the diode in the ordinary rectifier bridge. The principle is that the polarity is consistent, that is, the power FET is in the reverse conduction mode; the gate and source electrodes of the two low-side power FETs Q2 and Q4 are respectively connected to the output port of the optocoupler with respect to the negative pole of the rectified output voltage, and the two high The side power field effect transistors Q1 and Q3 respectively form an analog diode circuit with the voltage polarity discrimination drive circuit; the input terminals of the two photocouplers are connected in series with the current limiting resistor and then connected to the sinusoidal AC circuit before rectification, and the input port of the full bridge rectifier circuit is connected in series The sinusoidal AC circuit before the rectification is also connected after the inductor L1, the output port of the full-bridge rectification circuit is connected to the filter capacitor, and the circuit has no external control terminal. 2. The high-efficiency full-bridge rectifier circuit according to claim 1, wherein the analog diode circuit is composed of diode D5, high-speed voltage comparator IC3, field effect transistor Q1, resistors R9, R10, R5, R1 and capacitor C7 , where the cathode of diode D5, the non-inverting terminal of the high-speed voltage comparator, the negative terminal of the power supply, and the source of the field effect transistor Q1 are connected to each other to form a collinear line, and the drain of the field effect transistor is connected to the inverting terminal of the voltage comparator through the resistor R9, and the pull-up resistor R10 is connected to the positive terminal of the power supply and the output terminal of the high-speed voltage comparator, and the working voltage required by the voltage comparator is supplied externally.