CN104319986A - Power supply powering off method and power supply - Google Patents

Abstract

The embodiment of the present invention discloses a power shutdown method, which includes: receiving a shutdown signal, changing the conduction time of the main switch on the primary side of the transformer, or changing the switching frequency of the main switch on the primary side; detecting the input of the primary side on the secondary side of the transformer The volt-second product of the voltage in the conduction time or the control value corresponding to the volt-second product, or, the switching frequency of the primary side main switch is detected on the secondary side of the transformer; according to the volt-second product or the volt-second The control value corresponding to the product, or the switching frequency of the main switch on the primary side, controls the shutdown of the synchronous rectifier on the secondary side of the transformer. By adopting the invention, the self-excited oscillation can be effectively avoided when the machine is turned off, no additional circuit elements need to be added, the circuit area is small, the structure is simple, and the cost is low.

Description

A kind of power off method and power supply

This application is a divisional application of an invention application. The application date of the original application is December 20, 2012, and the application number is 201210558499.9. The name of the original application is a power shutdown method and a power supply

technical field

The invention relates to the field of power supplies, in particular to a method for shutting down a power supply and a power supply.

Background technique

In the low-voltage and high-current field, synchronous rectification technology has significant efficiency advantages over diode non-synchronous rectification, so it is widely used in switching power supplies. However, when the primary pulse width modulation (Pulse Width Modulation, PWM) control is applied to the isolated DC power supply, the driving signal of the secondary synchronous rectification circuit needs to be transmitted from the primary side to the secondary side. After the primary side shutdown control unit is turned off, the secondary side synchronous rectification The circuit is out of control. When the isolated DC power supply uses the secondary side synchronous rectification technology, the current in the output inductor can be bidirectional, and the output inductor current will become negative at light load. If the DC isolated power supply shuts down, the shutdown of the secondary side synchronous drive is uncontrolled, and the circuit is prone to uncontrollable self-excited oscillation after the primary side is shut down, thereby increasing the stress on the circuit components. In some cases, the self-excited oscillation will last for a long time, or even last forever, and affect the next startup. Fig. 1 is a waveform diagram before and after shutdown of the secondary freewheeling tube of the existing forward active clamp DC converter. As shown in Figure 1, when the power supply is turned off at t=550 microseconds, the waveform after shutdown is very dense, precisely because of the self-excited oscillation of the synchronous rectification circuit in the power supply.

In order to solve the problem of self-oscillation in the synchronous rectification circuit after shutdown, in the prior art, an optocoupler or a drive transformer is usually used to transmit the shutdown signal from the primary side to the shutdown control loop synchronously driven by the secondary side. Fig. 2 is a schematic diagram of an existing shutdown using an optocoupler control circuit. As shown in Fig. 2, after the shutdown signal is transmitted to the secondary control circuit through the optocoupler or other isolation devices, the secondary control circuit turns off the synchronous rectification circuit. However, whether optocouplers or other isolation devices are used to transmit shutdown signals, additional circuit elements are required in the circuit. And since the optocoupler or other isolation devices must meet the safety creepage distance requirements, the component area is relatively large. These all increase the size and cost of the circuit. In addition, at present, the shutdown time of the usual primary-side PWM shutdown control unit is random, that is to say, the shutdown time can occur at any time within a switching cycle, so even if an optocoupler or other isolation device is used to transmit the shutdown signal The delay time is so short that it can be ignored, and the current in the secondary output inductor may still be reversed when the light load is turned off, which will cause overvoltage or even avalanche breakdown of the secondary synchronous switch tube during shutdown.

Contents of the invention

The technical problem to be solved by the embodiments of the present invention is to provide a power supply shutdown method and a power supply. It can effectively avoid self-excited oscillation when shutting down.

In the first aspect, the embodiment of the present invention provides a power shutdown method, which may include: receiving a shutdown signal, changing the conduction time of the main switch of the primary side of the transformer; detecting the input voltage of the primary side on the secondary side of the transformer within the conduction time The volt-second product within or the control value corresponding to the volt-second product; according to the volt-second product or the control value corresponding to the volt-second product, the shutdown of the synchronous rectifier on the secondary side of the transformer is controlled to realize power shutdown .

In the second aspect, the embodiment of the present invention provides another power shutdown method, which may include: receiving a shutdown signal, changing the switching frequency (or switching period) of the primary side main switch of the transformer; detecting the primary side main switch on the secondary side of the transformer The switching frequency (or switching cycle) of the switch; according to the switching frequency (or switching cycle) of the main switch on the primary side, the shutdown of the synchronous rectifier on the secondary side of the transformer is controlled.

In the third aspect, the embodiment of the present invention provides a power supply, which may include: a shutdown control unit, configured to receive a shutdown signal, and change the conduction time of the main switch on the primary side of the transformer; a control value acquisition unit, used to Detecting the volt-second product of the primary side input voltage within the conduction time or the control value corresponding to the volt-second product; the secondary side control unit is used for according to the volt-second product or the control value corresponding to the volt-second product and controlling the turn-on and turn-off of the synchronous rectifier on the secondary side of the transformer.

In a fourth aspect, the embodiment of the present invention provides another power supply, which may include: a shutdown control unit, configured to receive a shutdown signal, and change the switching frequency (or switching cycle) of the primary side main switch of the transformer; a frequency detection unit (or cycle detection Unit) is used to detect the switching frequency (or switching period) of the primary main switch on the secondary side of the transformer; the secondary control unit is used to control the switching frequency (or switching period) of the primary main switch according to the primary side. The shutdown of the synchronous rectifier on the secondary side of the transformer is described.

It can be seen that the power supply shutdown method and the power supply provided by the embodiment of the present invention change the conduction time of the primary side main switch of the transformer by receiving the shutdown signal, or change the switching frequency of the primary side main switch; detect the primary side input voltage on the secondary side of the transformer The volt-second product or the control value corresponding to the volt-second product during the conduction time, or the switching frequency of the main switch on the primary side; according to the volt-second product or the control value corresponding to the volt-second product, or the original The switching frequency of the main switch on the side controls the shutdown of the synchronous rectifier on the secondary side of the transformer, and can adjust the switching circuit to the most favorable state for shutdown, and then turn off the primary side circuit and the secondary side according to the predetermined optimal shutdown sequence. Side synchronous rectification circuit, so as to effectively avoid shutdown oscillation and shutdown stress. There is no need to add new circuit elements, thereby saving the volume and cost of the circuit, the structure is simple, the cost is low, and the reliability and stability of the power supply are also improved.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Fig. 1 is the waveform diagram before and after shutdown of the secondary freewheeling tube of the existing forward active clamp DC converter;

Fig. 2 is the schematic diagram of the current shutdown using optocoupler control circuit;

FIG. 3 is a schematic flow chart of a power shutdown method provided by an embodiment of the present invention;

Fig. 4a is a schematic flow chart of another power shutdown method provided by an embodiment of the present invention;

Fig. 4b is a schematic flow chart of another power shutdown method provided by an embodiment of the present invention;

Fig. 5 is a schematic flow chart of another power shutdown method provided by an embodiment of the present invention;

FIG. 6 is a schematic diagram of a logic structure of a power supply provided by an embodiment of the present invention;

7 is a schematic circuit diagram of a shutdown control unit in a power supply according to an embodiment of the present invention;

FIG. 8 is a schematic diagram of a logical structure of another power supply provided by an embodiment of the present invention;

FIG. 9 is a schematic diagram of a logical structure of another power supply provided by an embodiment of the present invention;

Fig. 10 is a schematic diagram of a logic structure of another power supply provided by an embodiment of the present invention;

FIG. 11 is a signal timing diagram illustrating the power supply shown in FIG. 10;

Fig. 12 is a schematic diagram of a logic structure of another power supply provided by an embodiment of the present invention;

FIG. 13 is a flow chart of yet another power-off method provided by an embodiment of the present invention.

Detailed ways

The following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

Here, it should also be noted that, in order to avoid obscuring the present invention due to unnecessary details, only the device structure closely related to the solution according to the present invention is shown in the drawings, and the relationship with the present invention is omitted. Little other details.

Please refer to FIG. 3 , which is a schematic flowchart of a method for shutting down a power supply provided by an embodiment of the present invention. The method for shutting down a power supply can be applied to a self-driven synchronous rectification power supply. As shown, the method includes:

S101. Receive a shutdown signal, and change the conduction time of the main switch on the primary side of the transformer.

Optionally, the switching period of the main switch on the primary side may or may not be changed.

S102. Detect the volt-second product of the primary-side input voltage within the conduction time on the secondary side of the transformer or a control value corresponding to the volt-second product.

Optionally, the corresponding control value of the volt-second product may be a voltage value or a current value.

Specifically, the volt-second product is selected as the detection parameter here because the volt-second product parameter can be easily obtained according to the input voltage and conduction time of the secondary side, the circuit structure is simple, and the calculation and judgment are convenient. Of course, a timing counter can also be set in the circuit to detect the values of parameters such as the frequency, period, and pulse width of the PWM signal as a reference condition for judging whether to shut down.

S103. Control the shutdown of the synchronous rectifier on the secondary side of the transformer according to the volt-second product or a control value corresponding to the volt-second product.

It can be seen that the power supply shutdown method provided by the embodiment of the present invention changes the volt-second product of the input voltage detected by the secondary side by changing the conduction time of the main switch on the primary side, thereby adjusting the switch circuit to the most favorable state for shutdown, and then Shut down the primary side circuit and the synchronous rectification circuit of the secondary side according to the predetermined optimal shutdown sequence, so as to achieve the purpose of eliminating shutdown oscillation and shutdown stress. There is no need to add new circuit elements, which saves the volume and cost of the circuit.

Please refer to FIG. 4 a , which is a schematic flowchart of a method for shutting down a power supply provided by an embodiment of the present invention. In this embodiment, the method includes the following steps:

S201, receiving a shutdown signal, shortening the conduction time of the main switch on the primary side of the transformer.

Specifically, there are several ways to shorten the conduction time of the main switch on the primary side of the transformer, but not limited to the following ways: at least one switching period before the main switch on the primary side of the transformer is turned off can be shortened, and the period after the switching period can be shortened. The on-time of the switch is less than the on-time of the switch before the shortening of the switching period. It is also possible to shorten the pulse width in at least one switching cycle before the primary switch of the transformer is turned off. It is also possible to shorten at least one switching period before the primary switch of the transformer is turned off, and select one or more of the shortened switching periods, and shorten the pulse width in the one or more shortened switching periods.

Preferably, the pulse width can be shortened in the last cycle before the primary switch is turned off. Specifically, the high level of the pulse is shortened, so as to shorten the last conduction time before the switch is turned off. The pulse here can be a PWM pulse.

It should be noted that the change time of various parameters here can be completed at the moment when the main switch of the primary side is turned off, but it is measured by the switching cycle, which is beneficial to counting the detection value by cycle as a unit in the subsequent detection.

S202. Detect, on the secondary side of the transformer, the volt-second product of the input voltage at the primary side during the conduction time or a control value corresponding to the volt-second product.

The corresponding control value of the volt-second product may be a voltage value or a current value.

Specifically, the volt-second product is selected as the detection parameter here because the volt-second product parameter can be easily obtained according to the input voltage and conduction time of the secondary side, the circuit structure is simple, and the calculation and judgment are convenient. Of course, a timing counter can also be set in the circuit to detect the values of parameters such as the frequency, period, and pulse width of the PWM signal as a reference condition for judging whether to shut down.

S203. When the volt-second product or the control value corresponding to the volt-second product is less than or equal to a preset value, turn off the synchronous rectifier on the secondary side.

Specifically, the preset value here can be set with reference to the steady-state volt-second product when the circuit is working normally when the power supply is not shut down. Usually, the preset value can be set to be smaller than the steady-state Volt-second product.

Please refer to FIG. 4b , which is a schematic flowchart of a method for shutting down a power supply provided by an embodiment of the present invention. In this embodiment, the method includes the following steps:

S301, receiving a shutdown signal, and lengthening the conduction time of the primary side main switch of the transformer;

Specifically, there are several ways to lengthen the conduction time of the primary main switch of the transformer as follows, but not limited to the following ways: at least one switching period before the primary main switch of the transformer is turned off can be lengthened, and after lengthening the switching period The turn-on time of the switch is greater than the turn-on time of the switch before the lengthening of the switching cycle; or, the pulse width is lengthened in at least one switching cycle before the primary side main switch of the transformer is turned off; or, the lengthening of the primary side main switch of the transformer is off At least one switching period before the off-off, select one or more switching periods from the extended at least one switching period, and lengthen the pulse width in the one or more extended switching periods.

Preferably, the pulse width can be lengthened in the last period before the main switch of the primary side is turned off. Specifically, the high level of the pulse is lengthened, so as to prolong the last conduction time before the switch is turned off. The pulse here can be a PWM pulse.

It should be noted that the change time of various parameters here can be completed at the moment when the main switch of the primary side is turned off, but it is measured by the switching cycle, which is beneficial to counting the detection value by cycle as a unit in the subsequent detection.

S302. Detect the volt-second product of the primary side input voltage within the conduction time on the secondary side of the transformer or the control value corresponding to the volt-second product;

S303. When the volt-second product or the control value corresponding to the volt-second product is greater than or equal to a preset value, turn off the synchronous rectifier on the secondary side.

Specifically, the preset value here can be set to be greater than the steady-state volt-second product accordingly.

It can be seen that the power supply shutdown method provided by the embodiment of the present invention uses the original PWM signal or other signal transmission path of the circuit to send a group of shutdown pulses from the primary side to the secondary side before shutdown, which is different from the normal operating state. In order to detect and identify the secondary side circuit, at the same time, by using this group of special shutdown pulses, the switching circuit can be adjusted to the most favorable state for shutdown, and then the primary side circuit and the secondary side circuit can be turned off according to the predetermined optimal shutdown sequence. Synchronous rectification circuit, so as to eliminate shutdown oscillation and shutdown stress. There is no need to add new circuit elements, thereby saving the volume and cost of the circuit. Changing the switching cycle and/or changing the pulse width constitutes a variety of modes. One parameter can be changed alone or two parameters can be changed at the same time. It is only necessary to ensure that the shutdown pulse sent by the primary side is different from that in normal operation. Just pulse.

Please refer to Fig. 5, the embodiment of the present invention also provides a power shutdown method, the method includes:

S401. Receive a shutdown signal, and change the switching frequency of the main switch on the primary side of the transformer.

The turn-on time of the switch can be extended, kept constant, or shortened, which is not limited in this embodiment of the present invention.

S402. Detect the switching frequency of the main switch on the primary side at the secondary side of the transformer;

S403. Control the shutdown of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the main switch on the primary side.

In one implementation manner, the switching frequency of the main switch on the primary side of the transformer is increased after receiving the shutdown signal. The secondary side holds a preset value for the switching frequency, which can be set to be slightly higher than the normal switching frequency of the power supply. The secondary side detects the switching frequency, compares the switching frequency with the preset value, and turns off the synchronous rectifier on the secondary side when the detected switching frequency is higher than or equal to the preset value.

In another implementation manner, the switching frequency of the main switch on the primary side of the transformer is reduced after receiving the shutdown signal. The secondary side holds a preset value for the switching frequency, which can be set to be slightly lower than the normal switching frequency of the power supply. After the secondary side detects the switching frequency, the switching frequency is compared with the preset value, and when the detected switching frequency is lower than or equal to the preset value, the synchronous rectifier on the secondary side is turned off.

Of course, those skilled in the art can understand that changing the switching frequency is actually equivalent to changing the switching period. No matter the implementation scheme of detecting the switching frequency or detecting the switching period is common knowledge of those skilled in the art, it will not be repeated here. In addition, the technical solution of changing the conduction time and the technical solution of changing the switching frequency provided by the embodiment of the present invention can be realized simultaneously, as long as corresponding detection methods and preset values are set on the secondary side, the same purpose can be achieved.

Please refer to FIG. 6 , which is a schematic circuit diagram of a power supply according to an embodiment of the present invention. Figure 6 shows the half-bridge rectifier circuit. Those skilled in the art should understand that this is only exemplary, not limiting the present invention, and the present invention can also be applied to a full-bridge rectifier circuit or a current-doubler rectifier circuit. In the circuit of this embodiment, the power supply includes:

A shutdown control unit 101, configured to receive a shutdown signal and change the conduction time of the primary main switch of the transformer TX1;

In an implementation manner, the shutdown control unit 101 is used to shorten the conduction time of the main switch on the primary side of the transformer.

Specifically, there are several implementations as follows: shorten at least one switching cycle before the primary switch of the transformer is turned off; or, shorten the pulse width in at least one switching cycle before the primary switch of the transformer is turned off; or, shorten Select one or more of the shortened switching periods at least one switching period before the main switch of the primary side of the transformer is turned off, and shorten the pulse width in the one or more shortened switching periods.

In another implementation manner, the shutdown control unit 101 is configured to lengthen the conduction time of the primary side main switch of the transformer.

Specifically, there are several implementation methods as follows: lengthen at least one switching period before the primary main switch of the transformer is turned off; or, lengthen the pulse width in at least one switching period before the primary main switch of the transformer is turned off; or, Lengthen at least one switching period before the main switch of the primary side of the transformer is turned off, select one or more switching periods from the at least one lengthened switching period, and lengthen the pulse width in the one or more lengthened switching periods.

A control value acquisition unit 102, the control value acquisition unit is configured to acquire a control value corresponding to the volt-second product or the volt-second product of the primary side input voltage of the transformer within the conduction time;

In one implementation, the control value acquisition unit 102 detects the control value corresponding to the volt-second product of the primary side input voltage Vins in the conduction time on the secondary side of the transformer TX1; in other implementations, it can be in the circuit Set the timing counter to detect the value of the frequency, period, pulse width and other parameters of the PWM signal as a reference condition for judging whether to shut down.

The secondary side control unit 103 is configured to control the turn-on and turn-off of the synchronous rectifier on the secondary side of the transformer TX1 according to the volt-second product or a control value corresponding to the volt-second product.

In an implementation manner, when the volt-second product or the control value corresponding to the volt-second product is less than or equal to a preset value, the synchronous rectifier on the secondary side is turned off, so as to realize power shutdown.

For example, the shutdown control unit 101 shortens at least one switching cycle before the primary side main switch Q1 of the transformer TX1 is turned off, and the volt-second product detected by the control value acquisition unit 102 or the control value corresponding to the volt-second product is less than or equal to The preset value, at this time, the secondary side control unit 103 turns off the synchronous rectification circuit of the secondary side to complete the shutdown.

For another example, when the shutdown control unit 101 lengthens at least one switching cycle before the primary side main switch Q1 of the transformer TX1 is turned off, the volt-second product detected by the control value acquisition unit 102 or the control value corresponding to the volt-second product is greater than or equal to the preset value, at this time, the secondary side control unit 103 turns off the synchronous rectification circuit of the secondary side to complete the shutdown.

As shown in FIG. 6, the power supply circuit also includes: a modulation signal generator 104, a transformer TX1, a primary main switch Q1, a first secondary switch Q2, a second secondary switch Q3 and an LC filter; switches Q1, Q2 and Q3 can be a MOS tube or other active switches.

The modulation signal generator 104 is electrically connected to the shutdown control unit 101 for modulating the primary input voltage Vin; wherein the modulation signal generator 104 can be a pulse width modulation signal generator or a pulse frequency modulation Signal generator.

The shutdown control unit 101 is electrically connected to the primary side main switch Q1; the primary side main switch Q1 is used to control the closing and opening of the primary side circuit loop.

One end of the primary side main switch Q1 is connected to the primary side input voltage terminal Vin through the primary coil P1 of the transformer TX1, and the other end is grounded;

The control value acquisition unit 102 is connected between the secondary voltage input terminal Vins and the secondary control unit;

The secondary side control unit 103 is connected to the first secondary side switch Q2 and the second secondary side switch Q3;

The first secondary switch Q2 and the second secondary switch Q3 are connected to the LC filter;

Wherein, the primary primary switch Q1 , the first secondary switch Q2 and the second secondary switch Q3 are insulated gate field effect transistors. Of course, other suitable switching devices may also be used.

In this embodiment, preferably, an insulated gate field effect transistor is used as a switch for illustration.

As shown in FIG. 6, the LC filter circuit includes an output inductor L1 and a filter capacitor C1. One end of the output inductor L1 is connected to the secondary voltage input terminal Vins, and the other end is connected to the output voltage terminal Vo, and the output voltage terminal Vo is grounded through the filter capacitor C1. The source of the primary main switch Q1 is grounded, the gate is connected to the shutdown control unit 101 , and the drain is connected to the primary voltage input terminal Vin through the primary coil P1. The source of the first secondary switch Q2 is grounded, the gate is connected to the secondary control unit 103 , and the drain is connected to the secondary input voltage terminal Vins through the secondary coil S1 . The source of the second secondary switch Q3 is grounded, the gate is connected to the secondary control unit 103 , and the drain is connected to the output voltage terminal Vo through the output inductor L1 .

When shutdown is required, the shutdown control unit 101 receives the shutdown signal, and changes the switching cycle and/or changes the pulse width in at least one cycle before the primary side main switch Q1 of the transformer TX1 is turned off as required. Here, we choose to shorten the pulse width for illustration. Because the pulse width is shortened, the turn-on time Ton of the main switch Q1 on the primary side will be shortened. During the shortened conduction time Ton, the input voltage Vin of the primary side continues to induce the input voltage Vins of the secondary side on the secondary side, and the control value acquisition unit 102 receives the input voltage Vins of the secondary side, and calculates that the input voltage Vins of the secondary side is in conduction with the input voltage Vins of the secondary side. The volt-second product within the time Ton, that is, the calculated volt-second product of the primary-side input voltage Vin that is proportional to the secondary-side input voltage Vins within the conduction time Ton. The control value acquiring unit 102 may directly make a judgment according to the volt-second product, or may perform corresponding calculation according to the volt-second product to obtain a control value corresponding to the volt-second product one-to-one. In this embodiment, the control value acquisition unit 102 outputs the control value Vvs corresponding to the volt-second product of the primary input voltage Vin within the on-time Ton. Here, it should be noted that the control value Vvs may be a voltage value as shown in FIG. 6 , of course, according to the design requirements of the circuit, the control value may also be a current value. In this embodiment, since the shutdown control unit 101 shortens the pulse width, the conduction time Ton of the main switch Q1 on the primary side decreases, so the volt-second product of the input voltage Vins on the secondary side within the conduction time Ton decreases, and further The corresponding control value Vvs decreases. The secondary side control unit 103 detects the control value Vvs, and when the volt-second product is less than or equal to a preset value, the corresponding control value is also less than or equal to a certain preset value, triggering the secondary side control unit 103 to issue a control command to switch the first secondary side The switch Q2 and the second secondary switch Q3 are turned off, so that the circuit of the synchronous rectification circuit is disconnected, and the power supply is completely shut down.

It should be noted that when the power supply is working normally, the volt-second product of the input voltage Vin on the primary side during the on-time Ton basically maintains a fixed value, and the fixed value is proportional to the output voltage Vo. In this embodiment, the volt-second product when the power supply is in normal operation is converted into a steady-state volt-second product. When setting the preset value, it can be set according to the steady-state volt-second product. In this embodiment, the preset value can be set to be smaller than the corresponding control value of the steady-state volt-second product. When the power supply works normally, the primary side does not send a shutdown signal, the shutdown control unit 101 has no effect on the loop of the primary side circuit, and the conduction time of the primary side main switch Q1 remains in a normal state. At this time, the primary side input voltage Vin is in the conduction state The volt-second product within the on-time Ton is a steady-state volt-second product. The secondary side control unit 103 detects that the control value at this time is larger than the preset value, and normally controls the closed circuit or open circuit of the synchronous rectification circuit. When the power supply is to be shut down, the primary side sends a shutdown signal, the shutdown control unit receives the shutdown signal, shortens the pulse width, and the conduction time Ton of the main switch Q1 of the primary side is shortened, so that the input voltage Vin of the primary side within this conduction time Ton The volt-second product is reduced to be smaller than the preset value, so the secondary side control unit 103 no longer performs normal control operations on the synchronous rectification circuit, but directly issues instructions to control the first secondary switch Q2 and the second secondary switch Q3 to be turned off. The synchronous rectification circuit is disconnected, and the power supply is completely shut down.

Correspondingly, when the switching period is shortened (ie, the switching frequency is increased) or both the switching period and the pulse width are shortened, the situation is as described above;

When the switching period is extended or the switching period and pulse width are extended at the same time, the conduction time Ton of the main switch Q1 on the primary side will be extended, the volt-second product of the secondary input voltage Vins within the conduction time Ton will increase, and the control value Vvs will increase , when the volt-second product is greater than or equal to the preset value, the secondary side control unit 103 issues an instruction to control the first secondary switch Q2 and the second secondary switch Q3 to be turned off, so that the synchronous rectification circuit is disconnected and the power supply is completely shut down. At this time, the preset value is greater than the control value corresponding to the steady-state volt-second product. When the power supply is working normally, the primary side does not send a shutdown signal, the shutdown control unit 101 has no effect on the primary side circuit loop, and the conduction time Ton of the main switch Q1 remains in a normal state. At this time, the primary side input voltage Vin is within the conduction time Ton The volt-second product in is the steady-state volt-second product, and the secondary side control unit 103 detects that the control value at this time is smaller than the predetermined value, and normally controls the closed circuit or open circuit of the synchronous rectification circuit loop. As mentioned above, when the power supply is to be shut down, the primary side sends a shutdown signal, and the shutdown control unit responds to the shutdown signal by deliberately increasing the conduction time of the main switch, so that the volt-second product of the input voltage of the primary side during this conduction time increases, the control value Vvs increases to be greater than the predetermined value, so the secondary side control unit no longer performs normal control operations on the synchronous rectification circuit, but issues a command to disconnect the synchronous rectification circuit and completely shut down the power supply.

Of course, there may also be a situation where the two parameters of the switching period and the pulse width change oppositely. At this time, it is only necessary to determine which parameter is dominant. The specific control process is described above, and will not be repeated here.

The power supply provided by the invention can effectively avoid the self-excited oscillation generated when the power supply is turned off, and does not need to add new circuit elements, so the circuit area is small, the structure is simple, the cost is low, and the reliability and stability of the power supply are also improved. sex.

Please refer to FIG. 7 , which is a schematic circuit diagram of a shutdown control unit in a power supply according to an embodiment of the present invention.

In terms of the implementation of the PWM controller, the shutdown information transmission method provided by the present invention has the advantage of being simpler and easier to implement than the analog PWM control. In digital PWM control, since the PWM pulse width and cycle information before shutdown are known and can be stored in the controller, it is easy to compile a more complex and optimized shutdown pulse sequence. In analog PWM control, it is relatively difficult to use analog circuits to realize more complex and optimized shutdown pulse sequences, so it is necessary to simplify and optimize the shutdown pulse sequence as much as possible.

In this embodiment, the shutdown control unit includes an RC series circuit, a volt-second clamp comparator Volt-Second Clam and a shutdown pulse comparator Shutdown Pulse PWM.

The RC series circuit is connected between the primary side input voltage terminal Vin and ground;

The non-inverting input terminals of the volt-second clamp comparator Volt-Second Clam and the shutdown pulse comparator Shutdown PulsePWM are jointly connected between the resistance Rvsc and the capacitor Cvsc of the RC circuit through the volt-second clamp pin VSCLAMP, and the The thresholds of the volt-second clamp comparator Volt-Second Clam and the shutdown pulse comparator Shutdown Pulse PWM are different.

On the primary-side PWM shutdown control unit, an external RC circuit can be used to connect to the primary-side input voltage VIN, and a ramp voltage whose slope is proportional to the primary-side input voltage VIN is generated on the volt-second clamp pin VSCLAMP of the shutdown control unit. When the circuit is working normally, the peak value of the ramp voltage is controlled at a lower level by the feedback control loop or the volt-second clamp comparator Volt-Second Clam, and the ramp voltage is allowed to rise to a At a higher level, the shutdown pulse comparator Shutdown Pulse PWM generates a shutdown width pulse with an increased volt-second product.

As shown in Figure 7, at this time the threshold of the shutdown pulse comparator Shutdown Pulse PWM is 3V, and the threshold of the volt-second clamp comparator Volt-Second Clam is 2.5V. During normal operation, the slope voltage on the VSCLAMP pin is limited by the volt-second clamp comparator Volt-Second Clam, and the general peak voltage works around 1.5V-2V. The last extended shutdown pulse is generated by the shutdown pulse comparator Shutdown Pulse PWM, and the generated shutdown pulse width is 1.5-2 times that of the normal working pulse. The shutdown pulse width may be longer than a normal switching period. The length of the last wide shutdown pulse with increased volt-second product is not determined by the control loop and the volt-second clamp circuit, but by the voltage of the volt-second clamp pin VSCLAMP compared with the 3V threshold level by the shutdown pulse comparator Shutdown Pulse PWM Confirm later.

Of course, the detection of the secondary side control value acquisition unit can also be based on the volt-second product detection principle, which can be realized with a simple RC circuit and a voltage comparator.

It should be noted that the principle of the present invention is applicable to the transmission of shutdown information across the isolation interface in all isolated power supplies, including DC/DC, AC/DC, DC/AC, AC/AC and other types of isolated converters.

Certainly, the principle of the present invention is also applicable to the application of the PWM shutdown control unit on the secondary side, which transmits shutdown information from the secondary side to the primary side; and the principle of the present invention is applicable to analog control and digital control. It is inherently more convenient to use digital control to achieve optimal shutdown PWM pulse train.

Please refer to FIG. 8 , which is a circuit diagram of another power supply provided by an embodiment of the present invention.

In this embodiment, another implementation form of the shutdown control unit 101 is specifically shown. The shutdown control unit 101 includes a control switch 1011 , a drive unit 1012 , a charging and discharging unit 1013 , a comparator 1014 and a logic unit 1015 . The control switch 1011 is connected between the output terminal of the modulation signal generator 104 and the input terminal of the driving unit 1012 , and is closed or opened in response to a control signal from the logic unit 1015 . The driving unit 1012 is configured to receive the modulation signal from the modulation signal generator 104 via the control switch 1011 , and output the modulation signal to the control terminal of the primary main switch Q1 . The charging and discharging unit 1013 is connected between the control terminal of the primary main switch Q1 and the ground, and is used for charging according to the conduction time of the primary main switch Q1 , and sends an output value corresponding to the charging result to the comparator 1014 . The comparator 1014 is configured to receive the output value of the charging and discharging unit 1013, compare the output value with a reference value, and output the comparison result to the modulation signal generator 104 to control the operation of the modulation signal generator 104, so that when charging When the output value of the discharge unit 1013 is greater than the reference value, the modulation signal generator 104 is turned off, and on the other hand, the comparison result is output to the logic unit 1015 . The logic unit 1015 is configured to output a control signal according to the shutdown signal, the output of the comparator 1014, and the signal at the input of the drive unit 1012, so that when the shutdown signal indicates that the power supply is to be turned off, the control switch 1011 is turned off, and the switch 1011 is turned off. When the switch 1011 is controlled, the input terminal of the driving unit 1012 has a high level, so that the charging and discharging unit 1013 is charged, and when the output value of the charging and discharging unit 1013 is greater than the reference value, the control switch 1011 is turned on, so that the driving unit 1012 There is a low level on the input terminal to turn off the main switch on the primary side. It can be seen that when the power supply is to be shut down, the primary side sends a shutdown signal, and the shutdown control unit 101 responds to the shutdown signal by disconnecting the control switch 1011 to charge the charging and discharging unit 1013, and the charging time at this time is shorter than that of the power supply. The charging time in the normal state is long. When the output value corresponding to the charging result is greater than the reference value, the control switch 1011 is turned on. At this time, the input of the drive unit 1012 is pulled to a low level by the off modulation signal, and the primary side main switch Q1 is turned off so that the on-time Ton of the main switch Q1 increases. According to an example of the present invention, the reference value Vref can be set according to the design parameters of the circuit, so that the output value output by the charging and discharging circuit 1013 is less than the reference value Vref when the power supply is working normally, and the output value of the charging and discharging circuit 1013 is lower than the reference value Vref when the power supply is about to be shut down. The output value of the output will be greater than the reference value Vref. As mentioned above, when the power supply is to be shut down, the primary side sends a shutdown signal, and the shutdown control unit 101 responds to the shutdown signal by deliberately increasing the conduction time of the main switch through the charging and discharging unit 1013, so that the input voltage of the primary side is turned on here. The volt-second product within the time period increases, and the control value Vvs increases to be greater than the predetermined value, so the secondary side control unit no longer performs normal control operations on the synchronous rectification circuit, but issues a command to disconnect the synchronous rectification circuit and completely shut down the power supply.

Similarly, through the power supply according to the embodiment of the present invention, the power supply can be effectively shut down to avoid self-excited oscillation, and since no optocoupler device is used, the area is small, the cost is saved, the structure is simple, and the installation is convenient.

In the embodiment shown in FIG. 9 , it specifically shows that the control value acquisition unit 102 may include a charging circuit 1021 and a discharging circuit 1022 . The discharge circuit 1022 discharges the charging circuit 1021 at the beginning of the on-time of the main control switch, and then the charging circuit 1021 charges within the on-time Ton, and the voltage value corresponding to the charging result when the on-time Ton ends As the control value Vvs. Therefore, the control value obtaining unit 102 obtains the control value Vvs corresponding to the integral value of the input voltage Vins with respect to time, and outputs the control value Vvs to the secondary control unit 103 . The power-off principle of this embodiment is basically the same as that of the above-mentioned embodiments, and will not be repeated here.

In the embodiment shown in FIG. 10 , an implementation form of the shutdown control unit and the control value acquisition unit is specifically shown. In this embodiment, the modulation signal generator 104 is a PWM modulation signal generator, but those skilled in the art can understand that, according to different application requirements, PFM (Pulse frequency modulation, pulse frequency modulation) modulation can also be used in this embodiment Signal generator. The shutdown control unit 101 includes a charging and discharging circuit composed of a resistor R3, a capacitor C4, and a diode, a comparator U2, an AND gate U1, a control switch k1, and a drive unit U4, wherein R3 and C4 are connected in series between the control terminal of the primary switch Q1 and ground between, and D1 is connected across R3 to discharge C4. When the power supply is working normally, the shutdown signal is at low level, and the AND gate U1 outputs low level, the control switch k1 is closed, and the PWM signal is transmitted to the drive unit through the switch k1 to drive the main switch Q1 on the primary side. When the shutdown signal is high level, and the PWM modulation signal and U2 are also high level, the AND gate U1 outputs high level, the control switch k1 is turned off, the input of the drive unit U4 remains high level, and the output also maintains high level Level until the voltage of C4 is charged higher than Vref, the comparator U2 reverses to a low level, then the AND gate outputs a low level again, and the switch k1 is closed. At the same time, since the comparator U2 reverses to a low level, the change informs the PWM modulation signal generator to stop working, so that the PWM modulation signal becomes a low level, and the input of the drive unit U4 is pulled to a low level by the PWM modulation signal, The primary main switch Q1 is turned off. The period from the high level of the shutdown signal to the shutdown of the main switch Q1 on the primary side is the extended conduction time Ton. How long the extension is determined by the time constant of the charging and discharging circuit R3C4. Diode D1 is used to discharge capacitor C4. Capacitor C4 is constantly being charged and discharged, which will form a periodic sawtooth wave. When working normally, the amplitude of the sawtooth wave is not high, and the amplitude will increase significantly when the power is turned off.

In this embodiment, the charging circuit 1021 in the control value acquiring unit 102 includes a first capacitor C2 and a first resistor R1 connected in series, and the discharging circuit 1022 includes a second capacitor C3 connected in series and a second resistor R2, where C3 and R2 are The branch of R1 and C2 is connected in parallel, and both C3 and R2 are connected to the control terminal of the switch Q4, and the switch Q4 is connected across the two ends of C2 to discharge C2 when it is turned on.

In this embodiment, during the on-time Ton of the PWM modulation signal, the secondary winding S1 induces a secondary side input voltage Vins proportional to the primary side input voltage Vins. The differential circuit formed by the resistor R2 drives the switch Q4 with a very narrow pulse, so that Q4 is turned on for a moment, and the charge of the first capacitor C2 is discharged, and the voltage is pulled to 0V. During the on-time Ton, the first capacitor C2 is charged through the first resistor R1, and it is no longer charged when Ton ends. At this time, the voltage Vvs of the first capacitor C2 represents the integral of Vin to time during the Ton period, referred to as Volt-second product. Waiting for the next turn-on time Ton, the control value acquisition unit 402 will re-discharge and re-charge, and so on. When the power supply is working normally, the integral of Vin to time during the Ton period, that is, the volt-second product basically maintains a fixed value, and when the power is turned off, because the conduction time Ton is deliberately increased significantly, the volt-second product also increases significantly, and the control The value Vvs increases significantly. After the secondary side control unit 103 detects the significantly increased Vvs, it issues a command to turn off the switches Q2 and Q3 on the synchronous rectification circuit, and the power supply is completely shut down, preventing current backflow and suppressing self-excited oscillation. In this embodiment, the two driving signals (used to drive the switches Q2 and Q3 ) of the secondary side control unit 103 are input from the secondary windings S2 and S3 of the transformer.

FIG. 11 is a signal timing diagram illustrating the self-driven synchronous rectification power supply shown in FIG. 10 .

Fig. 11 shows the voltage Vg1 of the control terminal of the main control switch Q1, the voltages Vg2 and Vg3 of the control terminals of the switches Q2 and Q3 of the synchronous rectification circuit on the secondary side, and the time sequence of the control value Vvs output by the control value acquisition unit 102 picture. Referring to FIG. 11 , the last turn-on time Ton of the main switch Q1 on the primary side (the last period when Vg1 is at a high level) is longer than the previous turn-on time, because the shutdown control unit 101 increases the conduction time in response to the shutdown signal during shutdown Pass time Ton. It can be seen from FIG. 11 that during the increased on-time Ton, the control value Vvs output by the control value acquisition unit 102 increases to be greater than the control value Vvs in the normal state, exceeding a predetermined value. After the increased on-time Ton (that is, the last period in which Vg1 is high), Vg1 becomes 0, so that the main switch Q1 is turned off, and the control value Vvs exceeds a predetermined value, so the secondary side control unit 103 detects Significantly increased Vvs, issued a command to control the level of the control terminals of the switches Q2 and Q3 on the synchronous rectification circuit, the switches Q2 and Q3 are turned off, the power supply is completely shut down, and there is no self-excited oscillation phenomenon.

In the solution of the embodiment of the present invention, the shutdown signal may include but not limited to a shutdown signal triggered by actions such as remote shutdown, over-current protection, over-voltage protection, over-temperature protection, and under-voltage protection.

Referring to Fig. 12, another power supply is provided for the embodiment of the present invention, and the power supply includes:

The shutdown control unit 11 is used to receive the shutdown signal and change the switching frequency of the primary side main switch of the transformer;

The turn-on time of the switch can be extended, kept constant, or shortened, which is not limited in this embodiment of the present invention.

A frequency detection unit 12, configured to detect the switching frequency of the primary main switch on the secondary side of the transformer;

The secondary side control unit 13 is configured to control the shutdown of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the main switch on the primary side.

In one implementation, the shutdown control unit 11 is specifically configured to increase the switching frequency of the main switch on the primary side of the transformer; the secondary side control unit 13 is specifically used to: when the switching frequency of the main switch on the primary side is higher than or equal to the preset value, turn off the synchronous rectifier on the secondary side.

In another implementation, the shutdown control unit 11 is specifically configured to: reduce the switching frequency of the main switch on the primary side of the transformer; the secondary side control unit 13 is specifically configured to: when the switching frequency of the main switch on the primary side is lower than or equal to At the preset value, the synchronous rectifier on the secondary side is turned off.

For specific implementation, reference may be made to corresponding method embodiments. Those skilled in the art can understand that changing the switching frequency is actually equivalent to changing the switching period. No matter the implementation scheme of detecting the switching frequency or detecting the switching period is common knowledge of those skilled in the art, that is, the frequency detection unit 12 can also be used for period detection, and correspondingly, the preset value is set to correspond to the switching period under the normal state of the power supply value. There are various means for frequency detection and period detection, and those skilled in the art can choose according to requirements.

FIG. 13 is a flowchart of a method for shutting down a self-driven synchronous rectification power supply according to an embodiment of the present invention.

Referring to FIG. 13 , when the self-driven synchronous rectification power supply is to be shut down, the shutdown is performed according to the following steps.

In step S11, the primary side sends a shutdown signal, and the last on-time of the main switch on the primary side is increased at the primary side; at step S12, the volt-second product of the primary side input voltage at the secondary side is detected during the on-time; S13. When the volt-second product is greater than or equal to a predetermined value, turn off the synchronous rectification circuit on the secondary side, so as to shut down the power supply.

Through the description of the foregoing embodiments, the present invention has the following advantages:

Using the original PWM signal or other signal transmission path of the circuit, before shutting down, send a group of shutdown pulses from the primary side to the secondary side, or change the frequency of the switching tube of the primary side, so that the secondary side Circuit detection and identification, so as to realize the adjustment of the switching circuit to the most favorable state for shutdown, and then turn off the primary side circuit and the synchronous rectification circuit of the secondary side according to the predetermined optimal shutdown sequence, so as to eliminate shutdown oscillation and shutdown stress Purpose. There is no need to add new circuit elements, thereby saving the volume and cost of the circuit, the structure is simple, the cost is low, and the reliability and stability of the power supply are also improved. Changing the switching frequency and changing the pulse width constitutes a variety of modes. You can change a parameter alone or change two parameters at the same time. You only need to ensure that the corresponding parameters detected by the secondary side (such as volt-second product or switching cycle, etc.) ) is different from the parameter in the normal operating state.

Those of ordinary skill in the art can understand that all or part of the processes in the methods of the above embodiments can be implemented through computer programs to instruct related hardware, and the programs can be stored in a computer-readable storage medium. During execution, it may include the processes of the embodiments of the above-mentioned methods. Wherein, the storage medium may be a magnetic disk, an optical disk, a read-only memory (Read-Only Memory, ROM) or a random access memory (Random Access Memory, RAM), etc.

The above disclosures are only preferred embodiments of the present invention, and certainly cannot limit the scope of rights of the present invention. Therefore, equivalent changes made according to the claims of the present invention still fall within the scope of the present invention.

Claims (6)

1. A power shutdown method, characterized in that the method comprises: Receive the shutdown signal and change the switching frequency of the main switch on the primary side of the transformer; detecting the switching frequency of the main switch on the primary side at the secondary side of the transformer; The switching off of the synchronous rectifier on the secondary side of the transformer is controlled according to the switching frequency of the main switch on the primary side. 2. The method according to claim 1, wherein said changing the switching frequency of the primary side main switch of the transformer specifically comprises: Increase the switching frequency of the main switch on the primary side of the transformer; The controlling the shutdown of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the main switch on the primary side specifically includes: When the switching frequency of the main switch on the primary side is higher than or equal to a preset value, the synchronous rectifier on the secondary side is turned off. 3. The method according to claim 1, wherein said changing the switching frequency of the primary side main switch of the transformer specifically comprises: Reduce the switching frequency of the main switch on the primary side of the transformer; The controlling the shutdown of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the main switch on the primary side specifically includes: When the switching frequency of the main switch on the primary side is lower than or equal to a preset value, the synchronous rectifier on the secondary side is turned off. 4. A power supply, characterized in that the power supply comprises: The shutdown control unit is used to receive the shutdown signal and change the switching frequency of the main switch on the primary side of the transformer; a frequency detection unit, configured to detect the switching frequency of the primary main switch on the secondary side of the transformer; The secondary side control unit is configured to control the shutdown of the synchronous rectifier on the secondary side of the transformer according to the switching frequency of the main switch on the primary side. 5. The power supply according to claim 4, wherein the shutdown control unit is specifically configured to: increase the switching frequency of the primary switch of the transformer; The secondary side control unit is specifically configured to: turn off the synchronous rectifier of the secondary side when the switching frequency of the main switch of the primary side is higher than or equal to a preset value. 6. The power supply according to claim 1, wherein the shutdown control unit is specifically configured to: reduce the switching frequency of the main switch on the primary side of the transformer; The secondary side control unit is specifically configured to: turn off the synchronous rectifier of the secondary side when the switching frequency of the main switch of the primary side is lower than or equal to a preset value.