Short circuit protection control method, primary side control device, secondary side feedback device and switching power supply

Abstract

The invention discloses a short-circuit protection control method, a primary side control device, a secondary side feedback device and a switching power supply. The short-circuit protection control method comprises the following steps: converting a direct-current voltage output by a secondary side of the switching power supply into a first voltage signal; comparing the first voltage signal with a reference voltage and outputting a PWM signal; identifying whether the PWM signal is continuously invalid in the current first set time or not every first set time, and if yes, outputting a heavy load distinguishing signal; carrying out OR logic calculation on the PWM signal and the heavy load distinguishing signal and then outputting a superposition control signal; modulating, isolating and demodulating the superposed control signal, and then outputting a feedback control signal; detecting whether the feedback control signal is continuously invalid in the current second set time every second set time; if so, judging that the output of the switching power supply is short-circuited; otherwise, determining that the switching power supply outputs normally; wherein the first set time is smaller than the second set time. The invention can avoid switching power supply heavy load false triggering short circuit protection.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of power supply, and particularly relates to a short-circuit protection control method, a primary side control device, a secondary side feedback device and a switching power supply. BACKGROUND

[0002] The Chinese patent application with the application number 202510010649.X provides an isolated DC-DC power supply chip, which mainly innovates in the short-circuit protection control method, Figure 1 is a specific implementation principle block diagram of the primary side control device of the patent application applied to the switching power supply, Figure 2 is a flow chart of the short-circuit protection control method of the patent application applied to the switching power supply. The short-circuit protection control method comprises: an output voltage rectification detection step of converting an alternating current signal output by a transformer secondary side into a direct current voltage to obtain a first voltage signal VDIV representing the size of the direct current voltage; a comparison output step of comparing the first voltage signal with a reference voltage to output a PWM signal; a modulation step of modulating the PWM signal into a first modulation signal ISOP and a second modulation signal ISON; an isolation processing step of isolating the first modulation signal ISOP into a first isolated signal VIOP and isolating the second modulation signal ISON into a second isolated signal VION; a demodulation step of demodulating the first isolated signal VIOP and the second isolated signal VION into a feedback control signal FB, the feedback control signal FB being a narrow pulse signal; and an output short-circuit detection and protection execution step of determining whether the switching power supply output is short-circuited according to the feedback control signal FB and immediately shutting down the primary side drive when it is identified that the switching power supply output is short-circuited, and restarting soft start after a third set time. The conditions for determining the short-circuit of the switching power supply output in different working stages are as follows: in the soft start stage, if it is identified that the feedback control signal FB is equal to 1 for the first time but the duration is less than or equal to a first set time; or it is identified that the feedback control signal FB is continuously equal to 0 for a time greater than a second set time, then it is determined that the switching power supply output is short-circuited; and in the stable working stage, if it is identified that the feedback control signal FB is continuously equal to 0 for a time greater than the second set time, then it is determined that the switching power supply output is short-circuited.

[0003] The inventor of the present application found that in the above short-circuit protection control method, in the stable working stage, when the switching power supply is in a steady state with heavy load (non-short circuit) working state, the first voltage signal VDIV is always less than the reference voltage VREF of the feedback loop of the switching power supply, the feedback control signal FB=0, when the time of FB=0 is greater than the second set time, the output short-circuit detection and protection execution unit cannot determine whether the switching power supply is in a short circuit or a heavy load state, and there is a problem of false triggering of short-circuit protection. That is, the short-circuit protection mechanism of the scheme is too simple, and it cannot effectively distinguish between the real output short-circuit fault and the normal working state of heavy load, and this problem exists in the isolation DC-DC power supply chip using other control methods in the soft start stage. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to provide a short-circuit protection control method, a primary side control device, a secondary side feedback device and a switching power supply, which overcome the defect of false triggering of short-circuit protection in the prior art under heavy load, ensure that the switching power supply can work stably under the condition of non-short-circuit heavy load, even if the output capacity reaches the limit, avoid false triggering of short-circuit protection into the hiccup state, realize accurate discrimination of short-circuit protection, and activate the protection mechanism only when a real short-circuit protection occurs.

[0005] As a first aspect of the present application, the technical scheme of the provided short-circuit protection control method embodiment is as follows:

[0006] A short-circuit protection control method for realizing output short-circuit protection in a stable working stage of a switching power supply, wherein the switching power supply comprises a transformer, and the short-circuit protection control method comprises:

[0007] A voltage dividing step of converting a direct current voltage output by a secondary side of the switching power supply into a first voltage signal VDIV;

[0008] A comparison output step of comparing the first voltage signal VDIV with a reference voltage to output a PWM signal;

[0009] A heavy load distinguishing step of identifying whether the PWM signal is continuously invalid within a current first set time every first set time, and outputting a heavy load distinguishing signal OL_CTRL if the answer is yes;

[0010] An OR logic calculation step of performing OR logic calculation on the PWM signal and the heavy load distinguishing signal OL_CTRL to output a superimposed control signal PWM_OUT;

[0011] A feedback control signal generation step of modulating, isolating and demodulating the superimposed control signal PWM_OUT to output a feedback control signal FB, wherein the feedback control signal FB is consistent with the effectiveness of the superimposed control signal PWM_OUT.

[0012] an output short circuit detection and protection execution step, detecting whether the feedback control signal FB is continuously invalid in a current second set time every second set time; if yes, determining that the output of the switching power supply is short circuited, immediately shutting down the primary side drive, and restarting the switching power supply after a third set time; otherwise, determining that the output of the switching power supply is normal;

[0013] wherein the first set time < the second set time.

[0014] Preferably, the modulation is modulating the PWM signal into a first modulation signal ISOP and a second modulation signal ISON by an OOK modulation method.

[0015] Further, if the switching power supply includes two parallel outputs, when the switching power supply is started, if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the primary side drive is not sent; when the feedback control signal FB of the second output is invalid, the primary side drive is sent.

[0016] Further, if the switching power supply includes two parallel outputs, when the switching power supply is started, if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the switching power supply is not identified whether an output short circuit occurs; when the feedback control signal FB of the second output is invalid, the switching power supply is identified whether an output short circuit occurs.

[0017] Further, if the switching power supply includes two parallel outputs, when the switching power supply is started, if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the primary side drive is not sent, and the switching power supply is not identified whether an output short circuit occurs; when the feedback control signal FB of the second output is invalid, the primary side drive is sent, and the switching power supply is identified whether an output short circuit occurs.

[0018] As a second aspect of the present application, the provided primary side control device embodiment technical solutions are as follows:

[0019] A primary side control device applied to a switching power supply, the switching power supply including a transformer, characterized in that the primary side control device includes:

[0020] a demodulation unit configured to receive a first isolation signal VIOP and a second isolation signal VION, and demodulate the first isolation signal VIOP and the second isolation signal VION into a feedback control signal FB;

[0021] The output short circuit detection and protection execution unit is configured to detect whether the feedback control signal FB is continuously invalid within a current second setting time every second setting time: if yes, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the switching power supply is restarted after a third setting time; otherwise, it is determined that the output of the switching power supply is normal.

[0022] The first isolation signal VIOP is generated by the first modulation signal ISOP generated by the secondary side feedback device and processed by the isolation processing device; and the second isolation signal VION is generated by the second modulation signal ISON generated by the secondary side feedback device and processed by the isolation processing device.

[0023] The secondary side feedback device generates the first modulation signal ISOP and the second modulation signal ISON through the following circuit or unit:

[0024] The voltage dividing circuit is configured to convert a direct current voltage output by the secondary side of the switching power supply into a first voltage signal VDIV.

[0025] The comparison output unit is configured to compare the first voltage signal VDIV with a reference voltage and output a PWM signal.

[0026] The overload distinguishing unit is configured to identify whether the PWM signal is continuously invalid within a current first setting time every first setting time, and output an overload distinguishing signal OL_CTRL if yes.

[0027] The or logic calculation unit is configured to perform or logic calculation on the PWM signal and the overload distinguishing signal OL_CTRL and output a superimposed control signal PWM_OUT, and the feedback control signal FB and the superimposed control signal PWM_OUT have the same validity.

[0028] The modulation unit is configured to modulate the superimposed control signal PWM_OUT into the first modulation signal ISOP and the second modulation signal ISON.

[0029] The first setting time is less than the second setting time.

[0030] As a third aspect of the present application, the provided secondary side feedback device embodiment technical solution is as follows:

[0031] A secondary side feedback device applied to a switching power supply, wherein the switching power supply comprises a transformer, and the secondary side feedback device comprises:

[0032] The voltage dividing circuit is configured to convert a direct current voltage output by the secondary side of the switching power supply into a first voltage signal VDIV.

[0033] A comparison output unit is configured to compare the first voltage signal VDIV with a reference voltage and output a PWM signal.

[0034] A heavy load distinguishing unit is configured to identify whether the PWM signal is continuously invalid within a current first setting time every first setting time, and output a heavy load distinguishing signal OL_CTRL if the PWM signal is continuously invalid within the current first setting time.

[0035] An OR logic calculation unit is configured to perform OR logic calculation on the PWM signal and the heavy load distinguishing signal OL_CTRL and output a superimposed control signal PWM_OUT.

[0036] A modulation unit is configured to modulate the superimposed control signal PWM_OUT into the first modulation signal ISOP and the second modulation signal ISON.

[0037] The first modulation signal ISOP is isolated by an isolation processing device into a first isolated signal VIOP, and the second modulation signal ISON is isolated by the isolation processing device into a second isolated signal VION.

[0038] A demodulation unit is configured to receive the first isolated signal VIOP and the second isolated signal VION, and demodulate the first isolated signal VIOP and the second isolated signal VION into a feedback control signal FB, which is consistent with the validity of the superimposed control signal PWM_OUT.

[0039] An output short-circuit detection and protection execution unit is configured to detect whether the feedback control signal FB is continuously invalid within a current second setting time every second setting time, and determine that the output of the switching power supply is short-circuited if the feedback control signal FB is continuously invalid within the current second setting time, immediately turn off the primary side drive, and restart the switching power supply after a third setting time; otherwise, determine that the output of the switching power supply is normal.

[0040] The first setting time is less than the second setting time.

[0041] As a fourth aspect of the present application, the switching power supply embodiment technical solution is as follows:

[0042] A switching power supply comprises a transformer, wherein the switching power supply further comprises the primary side control device of any one of the second aspect, the isolation processing device, and the secondary side feedback device of any one of the third aspect.

[0043] Compared with the prior art, the application can ensure that the switching power supply quickly and effectively identifies whether to trigger the short-circuit protection mechanism in the closed-loop control stage to the maximum extent, thereby accurately and effectively protecting the stability, safety and reliability of the switching power supply. The specific beneficial effects are analyzed in detail as follows.

[0044] (1) In the embodiment of the application, when the switching power supply is in light load and normal load, the first voltage signal fluctuates around the reference voltage, and the PWM signal switches back and forth between effective and ineffective. By reasonably setting the second set time, the output short-circuit detection and protection execution step cannot detect the continuous invalidity of the feedback control signal within the second set time, so as to not trigger the short-circuit protection and avoid affecting the normal work of the switching power supply.

[0045] (2) In the embodiment of the application, when the switching power supply is in heavy load but has not entered the under-voltage protection state, the under-voltage protection threshold is ≤ the first voltage signal < the reference voltage, and the PWM signal is continuously invalid. If only the PWM signal is modulated, isolated and demodulated to output the feedback control signal, the feedback control signal will be continuously invalid, and the short-circuit protection will be triggered within the second set time. However, in the embodiment of the application, a heavy load distinguishing signal is output every first set time. Since the first set time < the second set time, after the or logical calculation of the heavy load distinguishing signal and the continuously invalid PWM signal, the continuity of the invalidity of the feedback control signal within the second set time will be destroyed, so that the switching power supply output is normal under this working condition, and the short-circuit protection is not triggered, thereby improving the stability of the switching power supply.

[0046] (3) In the embodiment of the application, when the switching power supply is in output short-circuit, the DC voltage output by the secondary side is pulled down to ground, and cannot provide the secondary side auxiliary power supply voltage, so that the PWM signal and the heavy load distinguishing signal cannot be generated, and the feedback control signal is continuously invalid, so that the switching power supply output is short-circuit under this working condition, and the primary side drive is immediately closed. After the third set time, the switching power supply is restarted, thereby improving the reliability of the switching power supply.

[0047] Other features and advantages of the application will be set forth in the following description of the application, and in part will become apparent to those skilled in the art from the description, or can be learned by practice of the application. The objects and other advantages of the application can be achieved and obtained by the structures specifically pointed out in the specification, claims and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0048] Figure 1 The primary side control device provided for the Chinese patent application 202510010649.X is applied to a specific embodiment principle block diagram of a switching power supply;

[0049] Figure 2The flow chart of the short-circuit protection control method for the Chinese patent application 202510010649.X is applied to the switching power supply;

[0050] Figure 3 The flow chart of the short-circuit protection control method for the first embodiment of the application;

[0051] Figure 4 The principle block diagram of a specific embodiment of the primary side control device and the secondary side feedback device for the second embodiment of the application applied to the switching power supply;

[0052] Figure 5 For Figure 4 The control timing chart of the switching power supply;

[0053] Figure 6 The control timing chart of the switching power supply output in parallel application. DETAILED DESCRIPTION

[0054] It should be noted that the embodiments in the present application and the features in the embodiments can be combined with each other without conflict.

[0055] In order to enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor should belong to the scope of protection of the present application.

[0056] It should be noted that the terms "first", "second" and the like in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily indicate a specific order or a chronological sequence. It should be understood that the data thus used can be interchanged under appropriate circumstances, so as to describe the embodiments of the present application. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion, for example, a process, method, system, product or device including a series of steps or units does not necessarily limit to those steps or units clearly listed, but can include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0057] It should be understood that when it is described that a step is followed by another step, the step may be directly followed by the other step or followed by the other step through a third step; when it is described that an element / unit is "connected" to another element / unit, the element / unit may be "directly connected" to the other element / unit or "connected" to the other element / unit through a third element / unit.

[0058] In addition, the drawings of the present disclosure are only schematic and not necessarily to scale. Identical or similar components are denoted by the same reference signs throughout the drawings and the detailed description, and a repeated description thereof will be omitted. Some of the block diagrams shown in the drawings are functional entities that do not necessarily have to correspond to physically or logically independent entities. These functional entities can be implemented by software, or in one or more hardware modules or integrated circuits, or in different network and / or processor devices and / or microcontroller devices.

[0059] First embodiment

[0060] The present embodiment provides a short-circuit protection control method applied to a switching power supply, the switching power supply comprising a transformer, Figure 3 The flowchart of the short-circuit protection control method of the first embodiment of the present disclosure, wherein the short-circuit protection control method comprises:

[0061] The voltage dividing step converts the DC voltage output by the secondary side of the switching power supply into a first voltage signal VDIV;

[0062] The comparison output step compares the first voltage signal VDIV with a reference voltage and outputs a PWM signal;

[0063] The overload distinguishing step identifies whether the PWM signal is continuously invalid within the current first set time every first set time, and outputs an overload distinguishing signal OL_CTRL if the answer is yes;

[0064] The OR logic calculation step performs OR logic calculation on the PWM signal and the overload distinguishing signal OL_CTRL and outputs a superimposed control signal PWM_OUT;

[0065] The feedback control signal generation step modulates, isolates and demodulates the superimposed control signal PWM_OUT and outputs a feedback control signal FB, the feedback control signal FB being consistent with the validity of the superimposed control signal PWM_OUT;

[0066] The output short circuit detection and protection execution step detects whether the feedback control signal FB is continuously invalid within the current second setting time every second setting time: if yes, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the switching power supply is restarted after the third setting time; otherwise, it is determined that the output of the switching power supply is normal.

[0067] The first setting time < the second setting time.

[0068] The working mechanism of the short circuit protection of the switching power supply in the embodiment is analyzed as follows:

[0069] (1) When the switching power supply is in light load and normal load, the first voltage signal VDIV fluctuates around the reference voltage, and the PWM signal switches back and forth between valid and invalid. By reasonably setting the second setting time, the feedback control signal FB is not continuously invalid within the second setting time in the output short circuit detection and protection execution step, and it is determined that the output of the switching power supply is normal.

[0070] (2) When the switching power supply is in heavy load but has not entered the under-voltage protection state, the under-voltage protection threshold ≤ the first voltage signal VDIV < the reference voltage, the PWM signal is continuously invalid, and a heavy load distinguishing signal OL_CTRL is output every first setting time. The or logic calculation is performed on the heavy load distinguishing signal OL_CTRL and the PWM signal, which breaks the continuity of the invalidity of the feedback control signal FB within the second setting time. Therefore, the feedback control signal FB is not continuously invalid within the current second setting time in the output short circuit detection and protection execution step, and it is determined that the output of the switching power supply is normal.

[0071] (3) When the output of the switching power supply is short-circuited, the direct current voltage VISO is pulled down to the ground, and the auxiliary supply voltage of the secondary side cannot be provided, so the PWM signal and the heavy load distinguishing signal OL_CTRL cannot be generated, and the feedback control signal FB is continuously invalid. Therefore, the feedback control signal FB is continuously invalid within the current second setting time in the output short circuit detection and protection execution step, and it is determined that the output of the switching power supply is short-circuited.

[0072] In specific implementation, the specific values of the times are not required, as long as the invention purpose can be achieved. For example, the first setting time can be 65 ms, the second setting time can be 200 ms, the length of the output heavy load distinguishing signal can be 2 us (i.e. a narrow pulse signal is output), and the third setting time can be 1 s (i.e. short circuit protection rest time).

[0073] As a specific implementation of the embodiment, the modulation step modulates the PWM signal into the first modulation signal ISOP and the second modulation signal ISON by the OOK modulation method.

[0074] As a specific embodiment of the present embodiment, if the switching power supply includes two parallel outputs, when the switching power supply is started and if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the primary side drive is not sent; when the feedback control signal FB of the second output is invalid, the primary side drive is sent, so as to avoid the reference voltage VREF of the feedback loop of the switching power supply of the two secondary sides being inconsistent due to process deviation, and the output voltage overshoot risk when one is in the primary side soft start stage and the other is in the stable working stage.

[0075] As a specific embodiment of the present embodiment, if the switching power supply includes two parallel outputs, when the switching power supply is started and if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the switching power supply is not identified whether an output short circuit occurs; when the feedback control signal FB of the second output is invalid, the switching power supply is identified whether an output short circuit occurs, so as to further avoid the output voltage overshoot risk.

[0076] As a specific embodiment of the present embodiment, if the switching power supply includes two parallel outputs, when the switching power supply is started and if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the primary side drive is not sent, and the switching power supply is not identified whether an output short circuit occurs; when the feedback control signal FB of the second output is invalid, the primary side drive is sent, and the switching power supply is identified whether an output short circuit occurs.

[0077] Second embodiment

[0078] The present embodiment provides a primary side control device applied to a switching power supply, the switching power supply including a transformer, Figure 4 As a specific embodiment of the present embodiment, the primary side control device and the secondary side control device of the second embodiment of the present application are applied to a switching power supply, wherein the primary side control device includes:

[0079] The demodulation unit is configured to receive the first isolation signal VIOP and the second isolation signal VION, and demodulate the first isolation signal VIOP and the second isolation signal VION into a feedback control signal FB.

[0080] The output short circuit detection and protection execution unit is configured to detect whether the feedback control signal FB is continuously invalid within a current second setting time every second setting time: if yes, it is determined that the switching power supply has an output short circuit, and the primary side drive is immediately turned off, and after a third setting time, the switching power supply is restarted; otherwise, it is determined that the switching power supply has a normal output.

[0081] The first isolation signal VIOP is generated by the first modulation signal ISOP generated by the secondary side feedback device and isolated by the isolation processing device; and the second isolation signal VION is generated by the second modulation signal ISON generated by the secondary side feedback device and isolated by the isolation processing device.

[0082] The secondary side feedback device generates the first modulation signal ISOP and the second modulation signal ISON through the following circuit or unit:

[0083] The voltage dividing circuit is used for converting the DC voltage VISO output by the secondary side of the switching power supply into the first voltage signal VDIV.

[0084] The comparison output unit is used for comparing the first voltage signal VDIV with the reference voltage and outputting the PWM signal.

[0085] The overload distinguishing unit is used for identifying whether the PWM signal is continuously invalid within the current first setting time every first setting time, and outputting the overload distinguishing signal OL_CTRL if yes.

[0086] The or logical calculation unit is used for performing or logical calculation on the PWM signal and the overload distinguishing signal OL_CTRL and outputting the superimposed control signal PWM_OUT, and the feedback control signal FB is consistent with the effectiveness of the superimposed control signal PWM_OUT.

[0087] The modulation unit is used for modulating the superimposed control signal PWM_OUT into the first modulation signal ISOP and the second modulation signal ISON.

[0088] The first setting time is less than the second setting time.

[0089] The technical means adopted by the control device of the embodiment is consistent with the control method of the first embodiment, and the working mechanism is the same, so it is not described in detail.

[0090] In addition, the preferred technical means or further improved means of each step in the control method of the first embodiment can be extended to the corresponding unit of the embodiment, and the embodiment will not be described one by one.

[0091] Third embodiment

[0092] The embodiment provided is a secondary side feedback device applied to a switching power supply, and the switching power supply comprises a transformer, please continue to see Figure 4 The secondary side feedback device comprises:

[0093] The voltage dividing circuit is used for converting the DC voltage output by the secondary side of the switching power supply into the first voltage signal VDIV.

[0094] A comparison output unit is configured to compare the first voltage signal VDIV with a reference voltage and output a PWM signal;

[0095] A heavy load distinguishing unit is configured to identify whether the PWM signal is continuously invalid within a current first setting time every first setting time, and output a heavy load distinguishing signal OL_CTRL if the PWM signal is continuously invalid within the current first setting time;

[0096] An OR logic calculation unit is configured to perform OR logic calculation on the PWM signal and the heavy load distinguishing signal OL_CTRL and output a superimposed control signal PWM_OUT;

[0097] A modulation unit is configured to modulate the superimposed control signal PWM_OUT into a first modulation signal ISOP and a second modulation signal ISON;

[0098] The first modulation signal ISOP is isolated by an isolation processing device into a first isolated signal VIOP, and the second modulation signal ISON is isolated by the isolation processing device into a second isolated signal VION. A primary side control device performs short-circuit protection control according to the first isolated signal VIOP and the second isolated signal VION through the following units:

[0099] A demodulation unit is configured to receive the first isolated signal VIOP and the second isolated signal VION, demodulate the first isolated signal VIOP and the second isolated signal VION into a feedback control signal FB, and make the feedback control signal FB consistent with the validity of the superimposed control signal PWM_OUT;

[0100] An output short-circuit detection and protection execution unit is configured to detect whether the feedback control signal FB is continuously invalid within a current second setting time every second setting time. If the feedback control signal FB is continuously invalid within the current second setting time, it is determined that the switching power supply is in output short-circuit, the primary side drive is immediately turned off, and the switching power supply is restarted after a third setting time. Otherwise, it is determined that the switching power supply is in normal output;

[0101] The first setting time is less than the second setting time.

[0102] The technical means adopted by the control device of the embodiment corresponds to the control method of the first embodiment, and the working mechanism is the same, so it is not described in detail;

[0103] In addition, the preferred technical means or further improved means of each step in the control method of the first embodiment can be extended to the corresponding units of the embodiment, and the embodiment will not be described one by one.

[0104] Fourth embodiment

[0105] The embodiment provides a switching power supply, which comprises a transformer, wherein the switching power supply further comprises the primary side control device in any one of the second embodiment, the isolation processing device and the secondary side feedback device in any one of the third embodiment.

[0106] Figure 5 For Figure 4 A control timing diagram of the switching power supply, VISO is a direct current voltage output by a secondary side of the switching power supply; UVLO is an under-voltage protection enable signal of the secondary side of the switching power supply; VDIV is a first voltage signal converted from the direct current voltage output by the secondary side of the switching power supply; VREF is a reference voltage of a secondary side feedback loop of the switching power supply; OL_CTRL is a heavy load distinguishing signal of the secondary side of the switching power supply; PWM is an output signal of the first voltage signal VDIV compared with the reference voltage; FB is a primary side feedback control signal of the switching power supply; and ZEMI_OUT is a signal output by an output short circuit detection and protection execution unit of the primary side of the switching power supply. Figure 5 To Figure 4 The working process of the switching power supply is analyzed as follows:

[0107] In the closed loop control process, when VDIV>VREF, PWM=1 (i.e. valid), the primary side feedback control signal FB=1 (i.e. valid), the primary side is not driven, and the secondary side output voltage VISO decreases; when VDIVVREF, PWM=0 (i.e. invalid), the primary side feedback control signal FB=0 (i.e. invalid), the primary side is driven, and the secondary side output voltage VISO increases, which may appear two cases:

[0108] Case one, if the secondary side output is shorted, VISO gradually decreases, VDIVVREF, PWM=0, the primary side feedback control signal FB=0, and when the time of FB=0 is greater than the second set time, it is determined that the switching power supply enters a short circuit state, the primary side drive is immediately closed, the short circuit protection waiting time is entered, and after the time ends, the soft start is restarted.

[0109] In case two, under the heavy load condition without short circuit, VISO gradually decreases, VDIV < VREF, PWM = 0, if the time of PWM signal continuously equal to 0 is greater than the first set time, the heavy load distinguishing unit outputs a fourth set time narrow pulse signal (i.e. heavy load distinguishing signal OL_CTRL), the signal and PWM signal are output as PWM_OUT signal through or logic, the PWM_OUT signal is modulated as feedback control signal FB through the modulation unit and demodulation unit, the output short circuit detection and protection execution unit is enabled to start output short circuit detection again, and whether the feedback control signal is continuously invalid in the next second set time is detected. If the time of PWM signal continuously equal to 0 is periodically greater than the first set time, the heavy load distinguishing unit outputs a narrow pulse signal OL_CTRL every first set time, the output short circuit detection and protection execution unit is enabled to start output short circuit detection again, and whether the feedback control signal is continuously invalid in the next second set time is detected. If the time of PWM signal continuously equal to 0 is less than or equal to the first set time, the narrow pulse signal OL_CTRL is not output, the output short circuit detection and protection execution unit is not enabled to start output short circuit detection again, and the switching power supply does not enter the short circuit state because the time of PWM signal continuously equal to 0 does not reach the second set time, and the switching power supply can maintain linear output under heavy load.

[0110] Figure 6 is a control timing diagram when the switching power supply is applied in parallel, VISO is the DC voltage output by the secondary side of the switching power supply; VREF1 is the reference voltage of the feedback loop of the secondary side of chip 1 (the chip of the first output); VREF2 is the reference voltage of the feedback loop of the secondary side of chip 2 (the chip of the second output); VDIV is the first voltage signal converted from the DC voltage output by the secondary side of the switching power supply; SOFT_EN1 is the switching power supply soft start enable signal of chip 1; SOFT_EN2 is the switching power supply soft start enable signal of chip 2; SECOND_EN1 is the switching power supply stable working enable signal of chip 1; SECOND_EN2 is the switching power supply stable working enable signal of chip 2; FB1 is the output feedback control signal of chip 1; FB2 is the output feedback control signal of chip 2, as shown in the figure, during the soft start process, the secondary side output voltage gradually rises, assuming VREF1 < VREF2, chip 1 enters the steady state working stage first, and chip 2 is in the soft start stage, at this time, since VDIV < VREF2, the feedback control signal FB2 of chip 2 = 0, the primary side is driven, and the secondary side output voltage will continue to rise, and VDIV > VREF1, the feedback control signal FB1 of chip 1 = 1, the primary side is not driven, so the output voltage overshoot in parallel output application can be avoided, and the output voltage can be stabilized near the rated voltage until chip 2 enters the steady state working stage.

[0111] The above merely preferred embodiments of the present application should not be considered as limiting the present application, and the protection scope of the present application should be defined by the scope of the claims. For those skilled in the art, several improvements and refinements can be made without departing from the spirit and scope of the present application, and these improvements and refinements should also be considered as falling within the protection scope of the present application.

Claims

1. A short-circuit protection control method for realizing output short-circuit protection in a steady operation phase of a switching power supply, the switching power supply comprising a transformer, characterized in that, The short-circuit protection control method comprises: a voltage dividing step of converting a direct current voltage output by the secondary side of the switching power supply into a first voltage signal VDIV; a comparison output step of comparing the first voltage signal VDIV with a reference voltage to output a PWM signal; a heavy load distinguishing step of identifying whether the PWM signal is continuously invalid within a current first set time every first set time, and outputting a heavy load distinguishing signal OL_CTRL if the PWM signal is continuously invalid; an OR logic calculation step of performing OR logic calculation on the PWM signal and the heavy load distinguishing signal OL_CTRL to output a superimposed control signal PWM_OUT; a feedback control signal generation step of modulating, isolating and demodulating the superimposed control signal PWM_OUT to output a feedback control signal FB, the feedback control signal FB being consistent with the validity of the superimposed control signal PWM_OUT; an output short-circuit detection and protection execution step of detecting whether the feedback control signal FB is continuously invalid within a current second set time every second set time, determining that the switching power supply is output short-circuited if the feedback control signal FB is continuously invalid, immediately shutting down the primary side drive, and restarting the switching power supply after a third set time; otherwise, determining that the switching power supply is output normally. The first set time is less than the second set time.

2. The short-circuit protection control method according to claim 1, characterized by: The modulation is modulation of the PWM signal into a first modulation signal ISOP and a second modulation signal ISON by an OOK modulation method.

3. The short-circuit protection control method of claim 1, wherein: If the switching power supply comprises two parallel outputs, when the switching power supply is started, if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the primary side drive is not sent; when the feedback control signal FB of the second output is invalid, the primary side drive is sent.

4. The short-circuit protection control method of claim 1, wherein: If the switching power supply comprises two parallel outputs, when the switching power supply is started, if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, whether the switching power supply is output short-circuited is not identified; when the feedback control signal FB of the second output is invalid, whether the switching power supply is output short-circuited is identified.

5. The short-circuit protection control method of claim 1, wherein: If the switching power supply comprises two parallel outputs, when the switching power supply is started, if the first output has entered a steady state and the second output is still in soft start, when the feedback control signal FB of the first output is valid, the primary side drive is not sent, and whether the switching power supply is output short-circuited is not identified; when the feedback control signal FB of the second output is invalid, the primary side drive is sent, and whether the switching power supply is output short-circuited is identified.

6. A primary side control device applied to a switching power supply, the switching power supply comprising a transformer, characterized in that, The primary side control device comprises: a demodulation unit configured to receive a first isolation signal VIOP and a second isolation signal VION, and demodulate the first isolation signal VIOP and the second isolation signal VION into a feedback control signal FB; The output short circuit detection and protection execution unit is configured to detect whether the feedback control signal FB is continuously invalid within a current second setting time every second setting time: if yes, it is determined that the output of the switching power supply is short-circuited, the primary side driving is immediately turned off, and the switching power supply is restarted after a third setting time; otherwise, it is determined that the output of the switching power supply is normal; The first isolation signal VIOP is generated by the first modulation signal ISOP generated by the secondary side feedback device and processed by the isolation processing device; and the second isolation signal VION is generated by the second modulation signal ISON generated by the secondary side feedback device and processed by the isolation processing device. The secondary side feedback device generates the first modulation signal ISOP and the second modulation signal ISON through the following circuit or unit: The voltage dividing circuit is configured to convert the direct current voltage output by the secondary side of the switching power supply into a first voltage signal VDIV. The comparison output unit is configured to compare the first voltage signal VDIV with a reference voltage and output a PWM signal. The overload distinguishing unit is configured to identify whether the PWM signal is continuously invalid within a current first setting time every first setting time, and output an overload distinguishing signal OL_CTRL if yes. The or logic calculation unit is configured to perform or logic calculation on the PWM signal and the overload distinguishing signal OL_CTRL and output a superimposed control signal PWM_OUT, and the feedback control signal FB and the superimposed control signal PWM_OUT have the same validity. The modulation unit is configured to modulate the superimposed control signal PWM_OUT into the first modulation signal ISOP and the second modulation signal ISON. The first setting time is less than the second setting time.

7. A secondary side feedback device applied to a switching power supply, the switching power supply comprising a transformer, characterized in that, The secondary side feedback device includes: The voltage dividing circuit is configured to convert the direct current voltage output by the secondary side of the switching power supply into a first voltage signal VDIV. The comparison output unit is configured to compare the first voltage signal VDIV with a reference voltage and output a PWM signal. The overload distinguishing unit is configured to identify whether the PWM signal is continuously invalid within a current first setting time every first setting time, and output an overload distinguishing signal OL_CTRL if yes. The or logic calculation unit is configured to perform or logic calculation on the PWM signal and the overload distinguishing signal OL_CTRL and output a superimposed control signal PWM_OUT. The modulation unit is configured to modulate the superimposed control signal PWM_OUT into the first modulation signal ISOP and the second modulation signal ISON. The first modulation signal ISOP is isolated and processed into the first isolation signal VIOP by the isolation processing device, the second modulation signal ISON is isolated and processed into the second isolation signal VION by the isolation processing device, and the primary side control device performs short circuit protection control according to the first isolation signal VIOP and the second isolation signal VION through the following unit: a demodulation unit, configured to receive the first isolated signal VIOP and the second isolated signal VION, and demodulate the first isolated signal VIOP and the second isolated signal VION into a feedback control signal FB, the feedback control signal FB being consistent with the superimposed control signal PWM_OUT validity; an output short circuit detection and protection execution unit, configured to detect whether the feedback control signal FB is continuously invalid within a current second setting time every second setting time: if yes, it is determined that the output of the switching power supply is short-circuited, the primary side drive is immediately turned off, and the switching power supply is restarted after a third setting time; otherwise, it is determined that the output of the switching power supply is normal. Wherein: the first setting time < the second setting time.

8. A switched mode power supply comprising a transformer, characterised by: The switching power supply further comprises the primary side control device of claim 6, the isolation processing device, and the secondary side feedback device of claim 7.

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