CN1238957C - A converter using a synchronous rectification circuit - Google Patents

Abstract

A converter using a synchronous rectification circuit, in particular a converter using a synchronous rectifier and combined with an LC damping circuit, mainly comprising a field effect transistor connected to one end of the secondary coil of the transformer of the converter and a group of resistors and capacitors connected in series to reduce oscillation and electromagnetic interference; the primary coil of the transformer of the converter has two diodes connected in series at both ends, an inductor is connected between the diodes, and the connecting end of the inductor and one of the diodes is connected to the connecting point of the transformer and the main switching element through a capacitor to form an LC damping circuit, so that the transformer of the converter can be reset and energy recovery can be achieved, thereby improving the efficiency of the converter.

Description

A converter using a synchronous rectification circuit

technical field

The present invention relates to a converter device, especially a converter comprising a synchronous rectifier and an LC snubber circuit arranged thereon, which eliminates the surge of the converter and enables the transformer of the converter to be reset , while allowing energy to be regenerated, thereby increasing its efficiency.

Background technique

Common communication systems require miniaturized and high-efficiency power supply modules to save space and energy. However, due to the conduction loss of the output current on the diode, it is difficult for the power supply module to have a preset efficiency. In recent years, integrated circuits have been widely used in computers and peripheral equipment, not only in industrial applications, but also in daily life. Although high-density integrated circuit equipment can have more uses and better functional improvements, its power The density will increase with the density of integrated circuits. In order to save energy loss, the operating voltage of these integrated circuits (ie, the output voltage of the power supply) should be reduced as much as possible. That is to say, under the concept that the computer uses low voltage and high current, it leads to the conduction loss of the output diode in the power supply, which also reduces the efficiency of the power supply.

In order to solve this problem, in addition to developing a nearly ideal diode (with the advantages of extremely small internal resistance and extremely low cut-in voltage), it is actually very difficult and almost impossible. The field effect transistor (MOSFET) synchronous rectifier (SR) can replace the traditional diode rectification circuit, and some active clamp circuits (active clamp) can further improve the efficiency of using the field effect transistor synchronous rectifier, but this method However, it is necessary to use such as auxiliary active switches and complex drive circuits.

As shown in Figure 1, it shows a circuit diagram of a single-ended forward converter using a field effect transistor synchronous rectifier circuit. The switch S2 in this circuit contains a field effect transistor Q1 and its parasitic diode D1 as a rectifier, and the switch S3 The field effect transistor Q2 and its parasitic diode D2 form a flywheel device. In order to reduce the conduction loss of the diode D2, a bypass capacitor C1 is used in Figure 2 to prolong the reset time of the transformer and prevent the field effect transistor Q1 from , Q2 are off at the same time, and due to the existence of the converter's parasitic inductance, the capacitor C1 will cause the converter to generate high-frequency oscillation, which will aggravate the problem of electromagnetic interference (EMI) and increase power loss.

Contents of the invention

In view of the shortcomings of the above-mentioned converter device, the present invention provides an improved converter device, which eliminates converter surge, reduces oscillation and electromagnetic interference, and achieves high efficiency.

According to one aspect of the present invention, there is provided a converter using a synchronous rectification circuit, the converter includes a transformer, and one end of the secondary coil of the transformer is connected to a field effect transistor rectifier composed of a field effect transistor and a parasitic diode The switch is characterized in that: the field effect transistor is connected in parallel with a group of resistors and capacitors connected in series; and one end of the primary coil of the transformer is connected to one end of a main switch, and the other end of the primary coil and the other end of the main switch are connected in series. Two diodes are connected, an inductor is connected between the two diodes, and the connecting end of the inductor and one of the diodes is connected to the connecting point of the primary coil and the main switch through a capacitor to form an LC snubber circuit .

Wherein, the converter can be a forward converter.

Wherein, the converter can be a flyback converter.

Wherein, the converter can be a half-bridge converter.

Wherein, the converter may be a converter combined with an energy regeneration circuit.

Wherein, the transformer of the converter is also connected with an inductance with a secondary coil, so that the inductance with a secondary coil is connected in series with the field effect transistor rectifier switch, and when the field effect transistor rectifier switch is opened, it may generate The energy of the voltage surge is regenerated to the voltage source, thus protecting the FET rectifier switch.

Wherein, the transformer of the converter has multiple sets of outputs.

According to another aspect of the present invention, there is provided a converter using a synchronous rectification circuit, the converter includes a transformer, and a field effect transistor is connected to one end of the secondary coil of the transformer, and is characterized in that the field effect transistor is connected in parallel with a group of resistors and capacitors connected in series; and one end of the primary winding of the transformer is connected to one end of a main switch with a diode and resistors and capacitors connected in parallel in series between the end and the other end of the main switch to form a RCD damping circuit.

Description of drawings

The main features and characteristics of the invention become apparent by describing the embodiments in detail with reference to the accompanying drawings:

FIG. 1 is a circuit diagram of a single-ended forward converter using a field effect transistor synchronous rectifier circuit in the prior art.

FIG. 2 is a circuit diagram of another single-ended forward converter using a field effect transistor synchronous rectifier circuit in the prior art.

Fig. 3 is a circuit diagram of a converter incorporating an LC snubber circuit according to the present invention.

Fig. 4 is a circuit diagram of a converter incorporating an RCD snubber circuit according to the present invention.

Fig. 5 is a graph comparing load characteristic efficiency curves of the LC snubber circuit and the RCD snubber circuit in the converter according to the present invention.

Fig. 6 is a graph comparing the input characteristic efficiency curves of the LC snubber circuit and the RCD snubber circuit in the converter according to the present invention.

FIG. 7 is a schematic waveform diagram of a converter incorporating an LC snubber circuit according to the present invention.

FIG. 8 is a schematic diagram of working state waveforms of a converter combined with an LC snubber circuit according to the present invention.

FIG. 9 is a circuit diagram of a converter combined with an LC snubber circuit according to the present invention, which is used to describe the working state of the converter in conjunction with FIGS. 7 and 8 .

FIG. 10 is a circuit diagram of a flyback converter using a synchronous rectifier circuit according to the present invention.

FIG. 11 is a circuit diagram of a half-bridge converter using a synchronous rectifier circuit according to the present invention.

Fig. 12 is a circuit diagram of a forward converter with synchronous rectification function equipped with a feedback current to form an energy regeneration circuit.

Fig. 13 is a circuit diagram of a flyback converter with synchronous rectification function equipped with a feedback current to form an energy regeneration circuit.

Detailed ways

As shown in Figure 3, a circuit of a converter according to the present invention is shown, wherein the field effect transistor circuits in the synchronous rectification circuit in the existing converter shown in Figure 2 are connected in parallel to each other in series Resistor R2 and capacitor C2 reduce high-frequency oscillation to eliminate electromagnetic interference and improve efficiency; add an LC damping circuit (Snubber) composed of inductor L, capacitor C, and diodes D3 and D4 to the primary coil of the transformer, that is, the One end of the primary coil of the transformer is connected to one end of the main switch S1, and the other end of the primary coil and the main switch are respectively connected in series with diodes D3 and D4, and an inductance L is connected between the two diodes D3 and D4, and the inductance The connection end of L and one of the diodes is connected to the primary coil of the transformer and the contact point of the main switch S1 through a capacitor C to form an LC snubber circuit. The operation of this LC snubber circuit is as follows. When the main switch S1 is open, the energy in the magnetic and leakage inductance will continue to guide the current through the diode D3 and the capacitor C without generating a voltage surge. During this period, the capacitor C Discharging, when the main switch S1 is turned on, the capacitor C and the inductor L resonate through the main switch S1 and the diode D4. During this period, the capacitor C is charged, so the converter is reset and the surge is eliminated without using any auxiliary active switch.

Moreover, in the open state of the main switch S1, the energy of the passive components stored in the main switch, the converter, and the connector will form energy regeneration.

Fig. 4 is a circuit diagram of a converter incorporating an RCD snubber circuit according to the present invention. The difference from that shown in Figure 3 is that the LC damping circuit is replaced, and an RCD damping circuit composed of resistor R3, capacitor C3 and diode D5 is added to the primary coil of the transformer to protect the main switch S1 from surges (turn-off surge).

As shown in FIG. 5 , it is a comparison diagram of the load characteristic efficiency of the converter combined with the LC snubber circuit shown in FIG. 3 and the converter combined with the RCD snubber circuit shown in FIG. 4 . Both converters are provided with field effect transistor synchronous rectifiers. It can be seen from Fig. 5 that when the forward transformer in the converter combined with the LC snubber circuit is at 4.14 amperes, the maximum efficiency can reach 90.9%, which is higher than that of the converter combined with the RCD snubber circuit.

As shown in FIG. 6 , it is a comparison chart of transformer efficiency in a converter combined with an LC snubber circuit and a converter combined with an RCD snubber circuit under various input voltages. The efficiency of the transformer combined with the LC damping circuit in the figure is still higher than that of the transformer combined with the RCD damping circuit. We can clearly find that the efficiency of the transformer will be increased by 10% by using the LC damping circuit instead of the RCD damping circuit. .

As shown in FIG. 7 , it shows the waveform of the converter using the LC snubber circuit according to the present invention. The abscissa in the figure is time, and V and I represent voltage and current respectively. Its main waveform corresponds to a switching cycle at rest. The above-mentioned cycle is shown in Figure 8, including 7 operating states. The main switch is conducting (ON) in two states, and open circuit (OFF) in 5 states. .

As shown in Figure 9, the operation of this converter is analyzed in detail as follows:

(1) State 1:

When the main switch S1 is open, the decompression capacitor C is discharged with the magnetic current of the converter and the output current. At the same time, the energy stored in the decompression inductor L will return to the voltage source Vi, because the polarity of the voltage passing through the capacitor C is not positive, in this state, the switch S2 is continuously turned on, and the secondary current of the converter is supplied to the load resistor R ₀ power supply .

(2) State 2:

This state starts when the induction current i _L reaches 0, and stops when the capacitor C discharges to zero.

(3) State 3:

The primary coil current _in1 continues to charge the capacitor C. When the energy is fully transferred to the capacitor C, the primary coil current _in1 will be 0, and at this time, the voltage V _C of the capacitor C will be charged to a certain voltage. The secondary coil voltage |V _n2 | will gradually rise due to the charging action of the capacitor C, and during the rising period, the switch S3 cannot be turned on immediately. The gradually increasing secondary coil voltage | _Vn2 | makes the diode D2 conduct at this moment, and the field effect transistor Q2 of the switch S3 is turned on at this moment.

(4) State 4:

The diode D3 reverses direction when the primary coil current i _n1 reaches 0, and the voltage V _C of the capacitor C is slightly discharged through the reverse current recovery of the diode D3 in state 4. At the same time, because the switching voltage V _S1 is higher than the voltage source Vi, there is The current flows in reverse through the primary winding n1 to the voltage source Vi. In this way, the energy is recovered. At this stage, the energy recovery is usually longer than the reverse recovery of the diode D3. At the end of state 4, the primary coil current i _n1 value is reached when the primary coil voltage V _n1 is 0 and the switching voltage V _S1 is equal to the voltage source Vi.

On the other hand, since the switch S3 is turned on, the switch voltage V _S2 is equal to the negative coil voltage V _n2 in this situation, because the capacitor C2 and the passive capacitance of the switch S2 will be charged by the reverse coil current _in2 , and the current will be Decreases to 0 at the end of this state.

(5) State 5:

The charged capacitor C2 can be used to prolong the on-state of FET Q2 in switch S3 even if the converter reset current drops to zero. Therefore, the flywheel current does not flow through the diode D2 of the switch S3, so as to avoid the large conduction loss of the secondary return voltage of the converter. After the primary coil current i _n1 is 0, a reverse voltage V _n1 will be induced through the diode D3 to the The capacitor C is charged, so that the reverse voltage of the secondary coil voltage V _n2 rises to keep the switch S3 in the conduction state. In the primary state, when the diode D3 is turned on, the switch voltage V _S1 is equal to the sum of the capacitor C voltage V _C and the voltage source Vi, The switching voltage V _S1 is kept below 2 times the voltage of the voltage source Vi.

(6) State 6:

When the main switch S1 is turned on, the current enters the primary coil n1 from the voltage source Vi through the switch S1, and the diode D4 will be forward-biased at the same time, the capacitor C will be discharged through the switch S1 and the diode D4, and the voltage V _n2 will be supplied to the load through the switch S2 resistor R ₀ . At this time, after a very short period of time, the reverse flywheel current i _S3 passes through the switch S3 , and the switches S2 and S3 are simultaneously turned on.

(7) State 7:

When the reverse recovery current of the diode D2 inside the switch S3 reaches 0, the main current will keep flowing through the primary coil n1 and the switch S1, and at the same time, the capacitor C will keep discharging; on the secondary side, the coil voltage V _n2 will continue to supply power to the load resistor R ₀ , the capacitor C is reversely charged through the diode D4 and the inductor L.

Besides the main embodiment of the forward converter with synchronous rectification described above, the converter according to the present invention can also be a flyback converter as shown in FIG. 10 or a half-bridge converter as shown in FIG. 11 .

In the embodiment shown in FIG. 12, a regenerative circuit is added on the forward converter shown in FIG. When the switch S2 is open, the energy of the voltage surge that may be generated is regenerated to the voltage source, thereby protecting the switch S2.

In the embodiment shown in FIG. 13, a regenerative circuit is added on the flyback converter shown in FIG. 10, and an inductance L2 with a secondary coil is connected to connect the primary coil of the inductance L2 to the switch S2. When the switch S2 is open, the energy of the voltage surge that may be generated is regenerated to the voltage source, thereby protecting the switch S2.

The above examples are only used to illustrate the present invention for convenience, and without departing from the spirit of the present invention, various simple deformations and modifications that can be made by those skilled in the art should still be included in the limited scope of the appended claims. in range.

Claims (8)

1. A converter using a synchronous rectification circuit, the converter includes a transformer, and one end of the secondary coil of the transformer is connected with a field effect transistor rectification switch composed of a field effect transistor and a parasitic diode, characterized in that: The field effect transistor is connected in parallel with a set of resistors and capacitors connected in series; and One end of the primary coil of the transformer is connected to one end of a main switch, the other end of the primary coil and the other end of the main switch are connected in series with two diodes, an inductor is connected between the two diodes, and the inductor and the other end of the main switch are connected in series. A connection terminal of one of the diodes is connected to the connection point of the primary coil and the main switch through a capacitor to form an LC snubber circuit. 2. The converter using a synchronous rectification circuit according to claim 1, wherein the converter is a forward converter. 3. The converter using a synchronous rectification circuit according to claim 1, wherein the converter is a flyback converter. 4. The converter using a synchronous rectification circuit according to claim 1, wherein the converter is a half-bridge converter. 5. The converter using a synchronous rectification circuit according to claim 1, characterized in that the converter is a converter combined with a circuit for realizing energy regeneration. 6. The converter using a synchronous rectification circuit according to claim 5, characterized in that, the transformer of the converter is also connected with an inductor with a secondary coil, so that the inductor with a secondary coil and the field effect transistor The rectifier switch is connected in series, so that when the field effect transistor rectifier switch is opened, the energy of the possible voltage surge can be regenerated to the voltage source, thereby protecting the field effect transistor rectifier switch. 7. The converter using a synchronous rectification circuit according to any one of claims 1 to 5, wherein the transformer of the converter has multiple sets of outputs. 8. A converter using a synchronous rectification circuit, the converter includes a transformer, and one end of the secondary coil of the transformer is connected to a field effect transistor, which is characterized in that the field effect transistor is connected in parallel with a group of resistors and capacitors connected in series; and One end of the primary coil of the transformer is connected to one end of a main switch, and a diode, resistance and capacitance connected in parallel are connected in series between the end of the main switch and the other end to form an RCD damping circuit.

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