WO2021088925A1

WO2021088925A1 - Forward-flyback switching power supply circuit

Info

Publication number: WO2021088925A1
Application number: PCT/CN2020/126761
Authority: WO
Inventors: 许梦羊; 张彦斌; 冯刚
Original assignee: 广州金升阳科技有限公司
Priority date: 2019-11-07
Filing date: 2020-11-05
Publication date: 2021-05-14
Also published as: CN110912409B; CN110912409A

Abstract

A forward-flyback switching power supply circuit, applied to a boosting occasion in which an output voltage is far higher than an input voltage, wherein the output voltage can be adjusted. A controllable switching device serves as a control switch; when output short circuit occurs or an output voltage is low, the controllable switching device is controlled to be switched off, so that the whole circuit works in a flyback state, and short circuit power consumption and output efficiency are greatly reduced; when the output voltage is high, the controllable switching device is switched on, so that the whole circuit works in a forward-flyback state, the voltage stress of a power tube of the whole circuit is reduced, device type selection is facilitated, and the efficiency of the whole machine is further improved.

Description

A forward and flyback switching power supply circuit

Technical field

The invention relates to the field of switching power supplies, in particular to a forward and flyback switching power supply circuit.

Background technique

Nowadays, high-voltage constant-current charging converters are used in many fields. Generally, the basic topology of flyback is applied to the field of outputting high-voltage and low-power. The voltage is increased by multi-winding or the multi-stage voltage doubler rectification formed by capacitors and diodes has reached The purpose of high output voltage, but the above methods have certain limitations:

The use of multi-winding rectification and then series output is equivalent to multiple flyback outputs in series. The higher the output voltage, the more windings are required. This is a challenge to the requirement of transformer volume. In addition, the pin spacing of the transformer needs to be further increased. Large, so the size of the entire transformer will be larger;

Using capacitors and diodes to double the voltage is only suitable for applications with small currents, and will be limited for applications with large output currents.

A specific circuit topology of a forward and flyback circuit in the prior art in this field is shown in FIG. 1.

The energy transmission efficiency is high. The structure of the transformer is also very simple. It only needs one winding to output a very high voltage. Compared with ordinary flyback doubling and rectification, the voltage of one winding is increased, so that the output voltage can be increased to higher.

But there is a fatal flaw. When the output is short-circuited or the output voltage is lower than the secondary winding voltage, the efficiency will drop sharply, and the loss of the primary side switch will increase sharply, which will affect the performance and reliability of the whole product. Especially for products with constant current source output, there will be no hiccup protection when short-circuited. Short-circuit is considered as the output voltage is equal to the forward voltage drop of the rectifier diode. At this time, the circuit working in the forward state will appear reverse. When the capacitors C1 and C2 are charged in reverse, the secondary winding of the transformer T1 will always be clamped at a negative voltage, and a large current will be formed in the flyback working state, and the duration is very long, resulting in magnetic The loss of the core and the primary side switch tube increases sharply. details as follows:

When the switching tube Q1 is turned on, the primary side 2 of the transformer T1 is positive, and the 1 terminal is negative. At this time, it belongs to the forward path. Then the primary side of the transformer T1 is excited and the energy is transferred to the secondary side at the same time, because 1 of the transformer T1 Terminals and terminal 3 are the same-named terminals. The energy transmission path of the secondary side is that the current flowing out of terminal 3 of transformer T1 goes back to terminal 4 of transformer T1 through capacitor C1, diode D3, capacitor C3, and capacitor C2 to form a forward loop. The capacitor is charged and the output voltage starts to build up. At this time, the capacitor C1 and the capacitor C2 are both positive and negative. When the primary side switch Q1 is turned off, the voltage across the transformer T1 is deflected, and the voltage on the secondary side of the transformer T1 will also be deflected, causing the 4 terminal to be positive and the 3 terminal to be negative, but the capacitors C1 and C2 Due to the reverse charging of the forward loop, the capacitors C1 and C2 must be discharged at the beginning of the flyback loop, and then charged in the direction. At this time, a large current will be formed and the loss will increase, and the output voltage will be very established. Slow, it will take a long time to get up. This is also one of the defects of this existing topology;

After multiple cycles of charging, the voltages of capacitor C1 and capacitor C2 will be positive and negative. When the primary switch Q1 is off, the flyback loop will charge capacitor C1 through diode D1, and capacitor C2 through diode D2 Charge, charge capacitor C3 through diode D1, diode D3 and diode D2. When the primary side switch tube Q1 is turned on, the forward loop is turned on, and the primary side energy will reversely charge the secondary side capacitors C1 and C2 through the transformer T1. At this time, the output voltage is equal to the sum of the voltage of the capacitor C1, the voltage of the capacitor C1, and the voltage of the secondary winding. When the output voltage is higher than the voltage on the secondary winding of the transformer T1, the voltages of the capacitors C1 and C2 will not be positive and negative, the current generated by the forward excitation will be small, and the loss will be small. When the output is short-circuited or When the output voltage is lower than the winding voltage, the duration of the forward loop will be longer, and the current on the primary side of the refraction transformer T1 will be larger, and the duration will be longer, and the loss will be greater. This is the existing forward and flyback Fatal flaws in the circuit cannot be short-circuited or output a lower voltage.

Summary of the invention

In view of this, the technical problem to be solved by the present invention is to propose a forward and flyback switching power supply circuit, which is applied to boost occasions where the output voltage is much higher than the input voltage. The transformer topology control is relatively simple and completely solves the output voltage. The problem of lower or sharp increase in loss caused by short circuit makes this topology easier to commercialize.

The inventive concept of the present invention:

A new control logic is proposed for the forward and reverse circuit topology of the existing transformer, which fundamentally solves the fatal defects of the existing circuit. The fundamental reason for the greater loss of the transformer's forward and flyback circuit in a short-circuit or low output voltage state is the existence of a forward path. The idea of the present invention is to disconnect the forward path when the output voltage is short-circuited or lower than the winding voltage. As shown in Figure 2, a switch Q2 is connected in series in the forward charging loop, and when the output voltage is short-circuited or lower , The switch Q2 is disconnected, and then the forward and flyback circuit will become a purely ordinary flyback circuit. The diode D1 and the capacitor C1 form a flyback output rectifier circuit, and the diode D3, the diode D2 and the capacitor C3 form another Flyback loop. Because the output voltage is low, the stress of the primary side switch tube Q1 will not be great. Moreover, during the start-up process, the output voltage starts to rise from zero, then it starts as an ordinary flyback circuit, the start-up capability will be enhanced, and the start-up time will be greatly shortened. After the output voltage reaches a certain value, the switch Q2 in the forward path is turned on. At this time, the circuit becomes a forward and flyback circuit. Such a control logic not only improves the ability to start the machine, but also solves the short circuit or low output voltage. The problem of high power consumption. There will be no influence on the stress of the primary side switch tube Q1.

The present invention is realized through the following technical solutions:

A forward and flyback transformer, which is used in boosting occasions where the output voltage is much higher than the input voltage. It includes a primary circuit, a transformer T1 and a secondary circuit. The secondary circuit specifically includes a diode D1, a diode D2, a diode D3, and a capacitor C1. , Capacitor C2, Capacitor C3; Terminal 1 of the primary winding of transformer T1 and terminal 3 of the secondary winding of transformer T1 are mutually homonymous, and terminal 4 of the secondary winding of transformer T1 is electrically connected to one end of capacitor C2 and connected to diode D1 The anode of the capacitor C2 is electrically connected to the anode of the diode D2, the cathode of the diode D2 is connected to the 3 end of the secondary winding of the transformer T1, the cathode of the diode D1 is electrically connected to one end of the capacitor C1 and connected to the anode of the diode D3, and the anode of the capacitor C1 The other end is electrically connected to the 3 ends of the secondary winding of the transformer T1, the cathode of the diode D3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the electrical connection point between the other end of the capacitor C2 and the anode of the diode D2. A controllable switching device for the timing of opening the forward path.

As a way of connecting the controllable switching device, one end of the controllable switching device is connected to the 4 ends of the secondary winding of the transformer T1, and the other end of the controllable switching device is connected to one end of the capacitor C2.

As another way of connecting the controllable switch device, one end of the controllable switch device is connected to the cathode of the diode D1, and the other end of the controllable switch device is connected to one end of the capacitor C1.

As another way of connecting the controllable switching device, one end of the controllable switching device is connected to the other end of the capacitor C2, and the other end of the controllable switching device is connected to the anode of the diode D2.

As another way of connecting the controllable switching device, one end of the controllable switching device is connected to the other end of the capacitor C1, and the other end of the controllable switching device is connected to the 3 ends of the secondary winding of the transformer T1.

Preferably, the controllable switching device is a switching tube, the drain of the switching tube is one end of the controllable switching device, and the source of the switching tube is the other end of the controllable switching device.

Preferably, the switch tube is a MOS tube.

Preferably, the controllable switching device is an IGBT, the drain of the IGBT is one end of the controllable switching device, and the source of the IGBT is the other end of the controllable switching device.

Preferably, the controllable switching device is a thyristor, the anode A of the thyristor is one end of the controllable switching device, and the cathode K of the thyristor is the other end of the controllable switching device.

Term explanation:

Electrical connection: includes direct or indirect connection, and also includes connection methods such as inductive coupling. For example, the “4-terminal electrical connection of the secondary winding of the transformer to one end of the capacitor C2” described in the present invention is a direct connection. When the switch tube is connected between the 4 ends of the secondary winding of the transformer and one end of the capacitor C2, it is an indirect connection.

Compared with the prior art, the present invention has the following beneficial effects:

1. A new forward and flyback circuit topology is proposed, a single circuit topology is switched to two circuit topologies, and the two topologies can be flexibly switched according to actual needs, and ordinary flyback topology is used when the voltage is low. The problem is that when the output voltage is high, the forward and flyback topology is used to solve the problems of poor start-up and large short-circuit power consumption caused by the original forward and flyback circuit;

2. The switching logic of the two topologies is clear and simple, only a switch tube is added to the forward loop to control, and through this control logic, the fatal defects of the existing forward and reverse circuits are solved, and the product's performance is improved. Performance and reliability, and cleverly reflect the advantages of flyback topology and forward and flyback topology;

3. The control logic is simple and flexible. It is feasible to cut off any point in the forward path. Without affecting the flyback loop, adding a switch tube to any point in the loop can achieve the same The effect is that the ingenious integration of the flyback circuit and the forward and flyback circuit makes it easier to realize product promotion.

Description of the drawings

Figure 1 is an existing forward and flyback switching power supply circuit;

2 is a schematic diagram of the first embodiment of the forward and flyback switching power supply circuit of the present invention;

3 is a schematic diagram of a second embodiment of a forward and flyback switching power supply circuit of the present invention;

4 is a schematic diagram of the third embodiment of the forward and flyback switching power supply circuit of the present invention;

Fig. 5 is a schematic diagram of a fourth embodiment of the forward and reverse switching power supply circuit of the present invention.

Detailed ways

Figure 2 shows the principle diagram of the forward and flyback switching power supply circuit of the present invention, which is applied to a high-voltage constant current converter, mainly by adding a switching tube Q2 to the forward loop to control the timing of opening the forward path.

The specific idea: connect a switching tube Q2 in series in the forward charging loop. When the output voltage is short-circuited or low, the switching tube Q2 is disconnected. At this time, the forward and flyback circuit will become a pure ordinary flyback circuit. The diode D1 and the capacitor C1 form a flyback output rectification loop, and the diode D3, the diode D2 and the capacitor C3 form another flyback loop. Because the output voltage is low, the stress of the primary side switch tube Q1 will not be great. And during the start-up process, the output voltage starts to rise from zero, then it starts as an ordinary flyback circuit, the start-up capability will be enhanced, and the start-up time will be greatly shortened. After the output voltage reaches a certain value, the switch Q2 in the forward path is turned on, and the circuit becomes a forward and flyback circuit at this time.

In order to enable those skilled in the art to better understand the present invention, the present invention will be further described below in conjunction with specific implementation circuits.

The first embodiment

Figure 2 shows a schematic diagram of the first embodiment of the forward and flyback switching power supply circuit of the present invention, including a primary side circuit, a transformer T1 and a secondary side circuit. The primary side circuit includes a switching tube Q1, and the drain of the switching tube Q1 is connected to the transformer T1 On the 2nd end of the primary winding, the source of the switching tube Q1 is grounded; the secondary side circuit specifically includes diode D1, diode D2, diode D3, capacitor C1, capacitor C2, capacitor C3, switching tube Q2, diode D4, and diode D4 as a switch The body diode of the tube Q2; the 1 end of the primary winding of the transformer T1 and the 3 end of the secondary winding of the transformer T1 are mutually homonymous ends, and the 4 ends of the secondary winding of the transformer T1 are connected to the drain of the switching tube Q2 and the diode D1 Anode, the source of the switch Q2 is connected to one end of the capacitor C2, the other end of the capacitor C2 is connected to the anode of the diode D2, the cathode of the diode D2 is connected to the 3 end of the secondary winding of the transformer T1, and the cathode of the diode D1 is connected to one end of the capacitor C1 and the diode The anode of D3, the other end of capacitor C1 is connected to terminal 3 of the secondary winding of transformer T1, the cathode of diode D3 is connected to one end of capacitor C3, and the other end of capacitor C3 is connected to the connection point between the other end of capacitor C2 and the anode of diode D2.

The working principle of this embodiment is as follows:

When the circuit starts, the output voltage starts to rise from zero, and the switch Q2 is not turned on at this time. When the switching tube Q1 is turned on, the primary circuit is a forward circuit, charging the capacitor C1 and the capacitor C2, but since the switching tube Q2 is not turned on, there is no forward circuit, so the energy generated by the excitation of the transformer T1 is stored in the magnetic core and is not released To the secondary side circuit, when the switch Q1 is turned off, the voltage across the transformer T1 reverses, and the secondary side circuit’s flyback rectification path opens the transformer T1 excitation energy and transmits it to the secondary side circuit. The whole process constitutes an ordinary flyback. When the energy is transmitted During the process, the output voltage slowly builds up to a certain value (this value is set by an external circuit), and the switch Q2 that controls the forward path is turned on, and the circuit works in the forward and reverse circuit at this time. The turn-on and turn-off of the switch Q2 is determined by the output voltage.

Second embodiment

The second embodiment is shown in FIG. 3, and the difference from the first embodiment is: the switch tube Q2 of the second embodiment uses an N-MOS tube and the series position is changed to between the diode D1 and the capacitor C1, and the leakage of the switch tube The pole is connected to the cathode of the diode D1, and the source of the switch tube is connected to one end of the capacitor C1.

The working principle of this embodiment is the same as that of the first embodiment, and will not be repeated here.

The third embodiment

The third embodiment is shown in FIG. 4, and the difference from the first embodiment is: the switch tube Q2 of the third embodiment uses a P-MOS tube and the series position is changed to between the diode D2 and the capacitor C2, and the leakage of the switch tube is The pole is connected to the other end of the capacitor C2, and the source of the switch tube is connected to the anode of the diode D2.

Fourth embodiment

The fourth embodiment is shown in FIG. 5, and the difference from the first embodiment is: the switch tube Q2 of the fourth embodiment uses a P-MOS tube and the series position is changed to between the secondary winding 3 end of the transformer T1 and the capacitor C1 In between, the source of the switch tube is connected to the other end of the capacitor C1, and the drain of the switch tube is connected to the 3 ends of the secondary winding of the transformer T1.

For the above preferred embodiments of the present invention, it should be pointed out that the above preferred embodiments should not be regarded as limiting the present invention. For those of ordinary skill in the art, without departing from the spirit and scope of the present invention, Several improvements and modifications have been made, for example, such as the modification of the same name end of the transformer T1, and the change of the switching tube Q2 to other devices that can achieve the same function, such as MOS tube, IGBT, thyristor, relay, etc., for the realization of this function All circuit changes, these improvements and modifications shall also be regarded as the protection scope of the present invention, and the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

A forward and flyback switching power supply circuit, applied to boost occasions where the output voltage is much higher than the input voltage, includes a primary side circuit, a transformer T1, and a secondary side circuit. The secondary side circuit specifically includes diodes D1, diode D2, diode D3, Capacitor C1, capacitor C2, capacitor C3; the first end of the primary winding of the transformer T1 and the third end of the secondary winding of the transformer T1 are mutually homonymous, and the fourth end of the secondary winding of the transformer T1 is electrically connected to the capacitor C2 One end is connected to the anode of the diode D1, the other end of the capacitor C2 is electrically connected to the anode of the diode D2, the cathode of the diode D2 is connected to the third end of the secondary winding of the transformer T1, and the cathode of the diode D1 is electrically connected to one end of the capacitor C1 and connected to the diode D3 The other end of the capacitor C1 is electrically connected to the third end of the secondary winding of the transformer T1, the cathode of the diode D3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the electrical connection between the other end of the capacitor C2 and the anode of the diode D2 Point, characterized in that it also includes a controllable switching device for controlling the opening timing of the forward path, one end of the controllable switching device is connected to the fourth end of the secondary winding of the transformer T1, and the other end of the controllable switching device is connected to the capacitor C2 One end.
A forward and flyback switching power supply circuit, applied to boost occasions where the output voltage is much higher than the input voltage, includes a primary side circuit, a transformer T1, and a secondary side circuit. The secondary side circuit specifically includes diodes D1, diode D2, diode D3, Capacitor C1, capacitor C2, capacitor C3; the first end of the primary winding of the transformer T1 and the third end of the secondary winding of the transformer T1 are mutually homonymous, and the fourth end of the secondary winding of the transformer T1 is electrically connected to the capacitor C2 One end is connected to the anode of the diode D1, the other end of the capacitor C2 is electrically connected to the anode of the diode D2, the cathode of the diode D2 is connected to the third end of the secondary winding of the transformer T1, and the cathode of the diode D1 is electrically connected to one end of the capacitor C1 and connected to the diode D3 The other end of the capacitor C1 is electrically connected to the third end of the secondary winding of the transformer T1, the cathode of the diode D3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the electrical connection between the other end of the capacitor C2 and the anode of the diode D2 It is characterized in that it also includes a controllable switching device for controlling the opening timing of the forward path, one end of the controllable switching device is connected to the cathode of the diode D1, and the other end of the controllable switching device is connected to one end of the capacitor C1.
A forward and flyback switching power supply circuit, applied to boost occasions where the output voltage is much higher than the input voltage, includes a primary side circuit, a transformer T1, and a secondary side circuit. The secondary side circuit specifically includes diodes D1, diode D2, diode D3, Capacitor C1, capacitor C2, capacitor C3; the first end of the primary winding of the transformer T1 and the third end of the secondary winding of the transformer T1 are mutually homonymous, and the fourth end of the secondary winding of the transformer T1 is electrically connected to the capacitor C2 One end is connected to the anode of the diode D1, the other end of the capacitor C2 is electrically connected to the anode of the diode D2, the cathode of the diode D2 is connected to the third end of the secondary winding of the transformer T1, and the cathode of the diode D1 is electrically connected to one end of the capacitor C1 and connected to the diode D3 The other end of the capacitor C1 is electrically connected to the third end of the secondary winding of the transformer T1, the cathode of the diode D3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the electrical connection between the other end of the capacitor C2 and the anode of the diode D2 It is characterized in that it also includes a controllable switching device for controlling the opening timing of the forward path, one end of the controllable switching device is connected to the other end of the capacitor C2, and the other end of the controllable switching device is connected to the anode of the diode D2.
A forward and flyback switching power supply circuit, applied to boost occasions where the output voltage is much higher than the input voltage, includes a primary side circuit, a transformer T1, and a secondary side circuit. The secondary side circuit specifically includes diodes D1, diode D2, diode D3, Capacitor C1, capacitor C2, capacitor C3; the first end of the primary winding of the transformer T1 and the third end of the secondary winding of the transformer T1 are mutually homonymous, and the fourth end of the secondary winding of the transformer T1 is electrically connected to the capacitor C2 One end is connected to the anode of the diode D1, the other end of the capacitor C2 is electrically connected to the anode of the diode D2, the cathode of the diode D2 is connected to the third end of the secondary winding of the transformer T1, and the cathode of the diode D1 is electrically connected to one end of the capacitor C1 and connected to the diode D3 The other end of the capacitor C1 is electrically connected to the third end of the secondary winding of the transformer T1, the cathode of the diode D3 is connected to one end of the capacitor C3, and the other end of the capacitor C3 is connected to the electrical connection between the other end of the capacitor C2 and the anode of the diode D2 Point, characterized in that: it also includes a controllable switching device for controlling the opening timing of the forward path, one end of the controllable switching device is connected to the other end of the capacitor C1, and the other end of the controllable switching device is connected to the secondary winding of the transformer T1 The third end.
The forward and flyback switching power supply circuit according to any one of claims 1 to 4, wherein the controllable switching device is a switching tube, and the drain of the switching tube is one end of the controllable switching device. The source is the other end of the controllable switching device.
The forward and flyback switching power supply circuit of claim 5, wherein the switch tube is a MOS tube.
The forward and flyback switching power supply circuit according to any one of claims 1 to 4, wherein the controllable switching device is an IGBT, the drain of the IGBT is one end of the controllable switching device, and the source of the IGBT is The other end of the controllable switching device.
The forward and flyback switching power supply circuit according to any one of claims 1 to 4, wherein the controllable switching device is a thyristor, and the anode A of the thyristor is one end of the controllable switching device, The K terminal of the cathode of the thyristor is the other terminal of the controllable switching device.