Switching power supply circuit and electronic equipment

Abstract

The invention relates to a switching power supply circuit and electronic equipment, according to the switching power supply circuit provided by the embodiment of the invention, when a secondary synchronous rectification scheme is used, a synchronous rectification module and an output switch module are arranged on a secondary side circuit, and when overcurrent is output, after switching tubes of the output switch module and the synchronous rectification module are controlled to be switched off, the output switch module is switched off; a body diode of a switch tube of the synchronous rectification module is used for output port follow current, compared with the conduction voltage drop when the switch tube is conducted, the conduction voltage drop of a secondary side circuit during follow current of the body diode is the tube voltage drop of the body diode, and the conduction voltage drop is much larger than the conduction voltage drop when the switch tube is over-current, and the conduction voltage drop of the synchronous rectification module is increased by increasing the conduction voltage drop of the synchronous rectification module. Therefore, the reflection voltage coupled to the primary winding is increased, the demagnetization time required when overcurrent is output is reduced, demagnetization is more in the same work period, the demagnetization capability in the work period is improved, the electric stress of a primary and secondary circuit power switch device is reduced, and the reliability of the power device is improved.

Description

Technical Field

[0001] The present application belongs to the field of power electronics technology, and in particular relates to a switching power supply circuit and electronic equipment. Background Art

[0002] The flyback topology is widely used in small and medium-power switching power supply designs. The secondary side of a flyback power supply typically uses a diode for freewheeling. While the diode's forward voltage drop is fixed, as the output current increases, the diode's losses increase significantly, making temperature rise difficult to address. This is particularly true in small adapters or power boards, where circuit board layout limitations preclude the use of multiple diodes in parallel or large heat sinks. Consequently, secondary synchronous rectification is the only solution. To further reduce product size, integrated synchronous rectification chips are widely used. However, this also presents some challenges. During output overcurrent, the demagnetization capability is low, and energy accumulates continuously during each switching cycle. This can cause the primary and secondary main power switching devices to withstand high electrical stress spikes, potentially exceeding their rated voltage rating and potentially even causing device breakdown. Summary of the Invention

[0003] The purpose of this application is to provide a switching power supply circuit and electronic equipment, aiming to solve the problems of low demagnetization ability of traditional switching power supplies using synchronous rectification chips on the secondary side, the main power switching devices being subjected to high electrical stress spikes, and the main power switching devices being easily damaged.

[0004] In a first aspect, an embodiment of the present application provides a switching power supply circuit, comprising an input port, a primary-side circuit, a transformer, a secondary-side circuit, and an output port connected in sequence, wherein the primary-side circuit includes a main power switch, and the primary winding of the transformer and the main power switch are connected between the input port and a ground terminal:

[0005] The secondary side circuit includes a synchronous rectification module and an output switch module; the synchronous rectification module is connected between one end of the secondary winding of the transformer and the output port, the output switch module is connected between the synchronous rectification module and the secondary winding, or between the synchronous rectification module and the output port, the synchronous rectification module includes a first switch tube, and when the output switch module and the first switch tube are turned off, the body diode of the first switch tube is the output port for freewheeling, thereby increasing the reflected voltage coupled to the primary winding.

[0006] In some embodiments, it further includes a switch control module, an input detection module, and an output detection module;

[0007] The input detection module is connected to the input port and the switch control module, and the switch control module is connected to the output switch module. The input detection module is configured to output a first driving voltage to the switch control module when the input voltage is greater than an input threshold;

[0008] The output detection module is connected to the secondary side circuit and the switch control module, and the output detection module is used to output a second driving voltage to the switch control module when the output current of the secondary side circuit is greater than an output threshold;

[0009] The switch control module is connected to the control end of the output switch module, and is used to turn off the output switch module when receiving the first driving voltage and the second driving voltage.

[0010] In some embodiments, the switch control module includes an on control circuit and an off control circuit;

[0011] The conduction control circuit is connected to the control terminal and the output port of the output switch module, and is used to control the conduction of the output switch module based on the output of the secondary side circuit;

[0012] The shutdown control circuit is connected to the control end of the output switch module, the input detection module and the output detection module, and is used to control the output switch module to be turned off according to the first driving voltage and the second driving voltage.

[0013] In some embodiments, the conduction control circuit includes a first resistor, a second resistor, a first diode, and a first capacitor;

[0014] The first end of the first resistor is connected to the output port, the second end of the first resistor is connected to the shutdown control circuit and the first end of the second resistor, the second end of the second resistor is connected to the anode of the first diode, the cathode of the first diode is connected to the control end of the output switch module, and the first capacitor is connected to the control end of the output switch module and the shutdown control circuit.

[0015] In some embodiments, the shutdown control circuit includes a first switch unit and a second switch unit;

[0016] The first end of the first switch unit is connected to the control end of the output switch module, the second end of the first switch unit is connected to the first end of the second switch unit, and the control end of the first switch unit is connected to the output detection module; the second end of the second switch unit is connected to the secondary ground of the power supply, and the control end of the second switch unit is connected to the input detection module.

[0017] In some embodiments, the input detection module includes a voltage divider module and a clamp module;

[0018] The input end of the voltage divider module is connected to the input port, the voltage divider output end of the voltage divider module is connected to the input end of the clamp module, and the output end of the clamp module is used to output the first driving voltage when the input voltage is greater than the input threshold.

[0019] In some embodiments, the clamping module includes a first voltage-stabilizing diode, and a cathode and an anode of the first voltage-stabilizing diode serve as an input terminal and an output terminal of the clamping module, respectively.

[0020] In some embodiments, the output detection module includes an operational amplifier, a second voltage-stabilizing diode, and a detection resistor. The first end of the detection resistor is connected to the secondary winding or the output port, the second end of the detection resistor is connected to the secondary ground of the power supply, the negative input end of the operational amplifier is connected to the first end of the detection resistor, the positive input end of the operational amplifier is connected to the secondary ground of the power supply, the output end of the operational amplifier is connected to the cathode of the second voltage-stabilizing diode, and the anode of the second voltage-stabilizing diode serves as the output end of the output detection module. The operational amplifier is used to amplify the detection voltage formed based on the output current loaded on the detection resistor, and output the second drive voltage when the detection voltage is greater than the breakdown voltage of the second voltage-stabilizing diode.

[0021] In some embodiments, the first switch unit includes a second switch tube and a third switch tube, the first end of the second switch tube is connected to the conduction control circuit, the second end of the second switch tube is connected to the first end of the second switch unit, and the control end of the second switch tube is connected to the output end of the output detection module; the first end of the third switch tube is connected to the control end of the output switch module, the second end of the third switch tube is connected to the first end of the second switch unit, and the control end of the second switch tube is connected to the output end of the output detection module.

[0022] In some embodiments, the second switch unit includes a photocoupler and a fourth switch tube, the input end of the light source of the photocoupler is connected to the power supply, the output end of the light source is connected to the first end of the fourth switch tube, the input end of the photoreceiver of the photocoupler serves as the first end of the second switch unit, the output end of the photoreceiver of the photocoupler serves as the second end of the second switch unit, the second end of the fourth switch tube is grounded, and the control end of the fourth switch tube serves as the control end of the second switch unit.

[0023] In some embodiments, the output switch module includes a fifth switch tube, and the control end of the fifth switch tube constitutes the control end of the output switch module;

[0024] The fifth switch tube is connected between the synchronous rectification module and the output port; or

[0025] The fifth switch tube is connected between the synchronous rectification module and the secondary winding.

[0026] In some embodiments, the synchronous rectification module includes a synchronous rectification chip, and the first switch tube is integrated into or externally mounted on the synchronous rectification chip;

[0027] The positive power supply pin, the secondary power supply ground pin, and the output voltage detection pin of the synchronous rectifier chip are connected to the first end of the secondary winding, the drain pin of the synchronous rectifier chip is connected to the output port, and the drain voltage detection pin of the synchronous rectifier chip is connected to the output port through the output switch module; or

[0028] The positive power pin of the synchronous rectifier chip is connected to the first end of the secondary winding through the output switch module, the secondary power ground pin and the output voltage detection pin of the synchronous rectifier chip are connected to the first end of the secondary winding, and the drain pin and the drain voltage detection pin of the synchronous rectifier chip are connected to the output port; or

[0029] The positive power supply pin, the secondary power supply ground pin, and the output voltage detection pin of the synchronous rectifier chip are connected to the output port, the drain pin of the synchronous rectifier chip is connected to the second end of the secondary winding, and the drain voltage detection pin of the synchronous rectifier chip is connected to the second end of the secondary winding through the output switch module; or

[0030] The positive power pin of the synchronous rectifier chip is connected to the output port through the output switch module, the secondary power ground pin and the output voltage detection pin of the synchronous rectifier chip are connected to the output port, the drain pin of the synchronous rectifier chip is connected to the second end of the secondary winding, and the drain voltage detection pin of the synchronous rectifier chip is connected to the second end of the secondary winding through the output switch module; or

[0031] The output voltage detection pin of the synchronous rectifier chip is connected to the output port through the output switch module, the power secondary ground pin and the power positive pin of the synchronous rectifier chip are connected to the output port, the drain pin of the synchronous rectifier chip is connected to the second end of the secondary winding, and the drain voltage detection pin of the synchronous rectifier chip is connected to the second end of the secondary winding through the output switch module.

[0032] In a second aspect, an embodiment of the present application provides an electronic device comprising the switching power supply circuit as described above.

[0033] Compared with the related art, the embodiments of the present application have the following advantages: the switching power supply circuit provided by the embodiments of the present application, when using a secondary synchronous rectification scheme, is provided with a synchronous rectification module and an output switch module in the secondary-side circuit. When the output is overcurrent, after the switches of the output switch module and the synchronous rectification module are turned off, the body diode of the switch of the synchronous rectification module is used to provide freewheeling current to the output port. Compared with the forward voltage drop of the switch when it is on, the forward voltage drop of the secondary-side circuit during freewheeling of the body diode is the tube voltage drop of the body diode, which is much larger than the forward voltage drop of the switch when it is overcurrent. In this way, by increasing the forward voltage drop of the synchronous rectification module, the reflected voltage coupled to the primary winding is increased, the demagnetization time required when the output is overcurrent is reduced, more demagnetization is achieved within the same working cycle, and the demagnetization capacity within the working cycle is improved, thereby reducing the electrical stress of the power switching devices in the primary and secondary circuits and improving the reliability of the power devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 A schematic diagram of a switching power supply circuit according to an embodiment of the present application;

[0035] Figure 2 A schematic diagram of a switching power supply circuit according to an embodiment of the present application;

[0036] Figure 3 A schematic diagram of a primary side circuit of a switching power supply circuit provided in an embodiment of the present application;

[0037] Figure 4 A schematic diagram of the structure of a synchronous rectification chip provided in one embodiment of the present application;

[0038] Figure 5 A schematic diagram of a secondary side circuit of a switching power supply circuit provided in an embodiment of the present application;

[0039] Figure 6 A schematic diagram of a switching power supply circuit according to an embodiment of the present application;

[0040] Figure 7 A schematic diagram of a switching power supply circuit according to an embodiment of the present application;

[0041] Figure 8 A partial circuit diagram of a switching power supply circuit provided in one embodiment of the present application;

[0042] Figure 9 This is a schematic diagram of another portion of a circuit of a switching power supply circuit provided in an embodiment of the present application. DETAILED DESCRIPTION

[0043] In order to make the technical problems, technical solutions and beneficial effects to be solved by this application more clearly understood, the present application is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain this application and are not intended to limit this application.

[0044] It should be noted that when an element is referred to as being “fixed on” or “disposed on” another element, it may be directly on the other element or indirectly on the other element. When an element is referred to as being “connected to” another element, it may be directly connected to the other element or indirectly connected to the other element.

[0045] It should be understood that the terms "length", "width", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc., indicating the orientation or position relationship, are based on the orientation or position relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on this application.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features. Throughout the description of this application, "plurality" means two or more, unless otherwise specifically defined.

[0047] See also Figure 1 and Figure 2 An embodiment of the present application provides a switching power supply circuit that can be used in any electronic device, including an input port 11, a primary side circuit 12, a transformer T1, a secondary side circuit 13, and an output port 14 connected in sequence. The primary side circuit 12 includes a main power switch, and the primary winding Np of the transformer T1 and the main power switch are connected between the input port 11 and the ground.

[0048] See also Figure 3 In some embodiments, the primary side circuit 12 further includes a startup circuit 121 and a switching power supply chip U1. Figure 3 In this example, the main power switch is integrated into the switching power supply chip U1. In other embodiments, the main power switch can also be an independent device adapted to the corresponding switching power supply chip. The main power switch is, for example, a MOS transistor.

[0049] When the main power switch is external to the switching power supply chip U1, the drain of the main power switch is connected to one end of the primary winding Np of the transformer T1, and the gate is connected to the drive pin of the switching power supply chip U1. When the main power switch is integrated within the switching power supply chip U1, the drain of the main power switch is connected to the switch pin (or drain pin) DRAIN of the switching power supply chip U1. The positive electrode of the input port 11 is connected to the switch pin DRAIN through the primary winding Np of the transformer T1. The current sampling pin CS of the switching power supply chip U1 is connected to the primary ground of the power supply through the sampling resistor R0. The auxiliary winding N2 and the startup circuit 121 are connected to the power supply pin VCC of the switching power supply chip U1. The startup circuit 121 is connected to the positive electrode of the input port 11. The startup circuit 121 generally includes a current limiting resistor R13 and capacitors C3 and C4.

[0050] In some embodiments, the flyback switching power supply is generally further provided with a clamping circuit 15 connected across the primary winding Np to absorb the voltage and current spikes generated during the high-frequency turn-on and turn-off of the main power switch. Input port 11 may include a rectifier bridge and a filter capacitor for receiving AC voltage; input port 11 may also be a DC input for receiving DC power.

[0051] See also Figures 1 to 4 The secondary side circuit 13 includes a synchronous rectifier module 131 and an output switch module 132; the synchronous rectifier module 131 is connected between one end of the secondary winding Ns of the transformer T1 and the output port 14, and the output switch module 132 is connected between the synchronous rectifier module 131 and the secondary winding Ns (see Figure 1 ), or connected between the synchronous rectification module 131 and the output port 14 (see Figure 2 ), the synchronous rectifier module 131 includes a first switch tube M1. When the output switch module 132 and the first switch tube M1 are turned off, the synchronous rectifier module 131 uses the body diode D0 of the first switch tube M1 as the output port 14 for continuous current flow, thereby increasing the reflected voltage coupled to the primary winding Np.

[0052] In the synchronous rectifier module 131, the first switch M1 is, for example, a MOS transistor, which can be an integrated chip device or an independent device. When the output of the secondary-side circuit 13 is normal, the output switch module 132 and the synchronous rectifier module 131 are turned on, and the switching power supply circuit operates normally. When the input and / or output of the switching power supply circuit are abnormal, such as overvoltage, overcurrent, or short circuit, the output switch module 132 will be turned off. When the synchronous rectifier module 131 detects an output abnormality of the secondary-side circuit 13 based on the shutdown of the output switch module 132, it also turns off its first switch M1. At this time, the energy of the secondary winding Ns will be released to the output port 14 through the body diode D0 of the first switch M1. Compared with the conduction voltage drop when the secondary-side circuit 13 output is normal, the conduction voltage drop using the body diode D0 to conduct the conduction is greatly increased, thereby increasing the reflected voltage coupled to the primary winding Np. In a flyback switching power supply circuit, the greater the reflected voltage, the shorter the demagnetization time required for the primary winding Np. This allows for more demagnetization within the same operating cycle, reducing the electrical stress on the power devices in the primary circuit 12 and the secondary circuit 13. Therefore, by reducing the required demagnetization time and achieving more demagnetization within the same operating cycle, the electrical stress on the primary and secondary power switching devices is reduced, thereby improving the reliability of the power switching devices.

[0053] In some embodiments, a capacitor is further connected in series to the positive power pin of the synchronous rectifier chip.

[0054] See also Figure 5 In some embodiments, the output switch module 132 includes a fifth switch tube Q1, the synchronous rectification module 131 includes a synchronous rectification chip U2, and the control end of the fifth switch tube Q1 constitutes the control end of the output switch module 132;

[0055] The fifth switch tube Q1 is connected between the synchronous rectification module 131 and the output port 14; or

[0056] The fifth switch Q1 is connected between the synchronous rectification module 131 and the secondary winding Ns.

[0057] In one example, the drain of the MOS transistor is connected to the output port 14, and the source is connected to the drain voltage detection pin VD of the synchronous rectifier chip U2. In another example, the MOS transistor is connected between one end of the secondary winding Ns and the positive power supply pin VCC or the output voltage detection pin VO of the synchronous rectifier chip U2. It will be understood that the key function of the output switch module 132 is to block the synchronous rectification of the synchronous rectifier chip U2. The connection position of the fifth switch Q1 may vary slightly depending on the synchronous rectifier chip U2 used. Figure 3In the example, the synchronous rectifier chip U2 and the fifth switch tube Q1 are arranged on the high-voltage side of the secondary side circuit 13. Depending on the selection of the synchronous rectifier chip U2, they can also be placed on the low-voltage side. This does not affect the realization of the synchronous rectification and blocking synchronous rectification functions, and the corresponding connection relationship is not given as an example here.

[0058] See also Figure 5 In some embodiments, the synchronous rectifier chip U2 is disposed on the high-voltage side of the secondary circuit 13:

[0059] The positive power supply pin VCC, the secondary power supply ground pin VSS_1 / 2, and the output voltage detection pin VO of the synchronous rectifier chip U2 are connected to the first end of the secondary winding Ns, the drain pin Drain_1 / 2 / 3 of the synchronous rectifier chip U2 is connected to the output port 14, and the drain voltage detection pin VD of the synchronous rectifier chip U2 is connected to the output port 14 through the output switch module 132; or

[0060] The positive power supply pin VCC of the synchronous rectifier chip U2 is connected to the first end of the secondary winding Ns through the output switch module 132, the secondary power supply ground pins VSS_1 / 2 and the output voltage detection pin VO of the synchronous rectifier chip U2 are connected to the first end of the secondary winding Ns, and the drain pins Drain_1 / 2 / 3 and the drain voltage detection pin VD of the synchronous rectifier chip U2 are connected to the output port 14; or

[0061] The positive power supply pin VCC, the secondary power supply ground pin VSS_1 / 2, and the output voltage detection pin VO of the synchronous rectifier chip U2 are connected to the output port 14, the drain pin Drain_1 / 2 / 3 of the synchronous rectifier chip U2 is connected to the second end of the secondary winding Ns, and the drain voltage detection pin VD of the synchronous rectifier chip U2 is connected to the second end of the secondary winding Ns through the output switch module 132; or

[0062] In some embodiments, the synchronous rectifier chip U2 is disposed on the low-voltage side of the secondary circuit 13:

[0063] The positive power supply pin VCC of the synchronous rectifier chip U2 is connected to the output port 14 through the output switch module 132, the secondary power supply ground pins VSS_1 / 2 and the output voltage detection pin VO of the synchronous rectifier chip U2 are connected to the output port 14, the drain pins Drain_1 / 2 / 3 of the synchronous rectifier chip U2 are connected to the second end of the secondary winding Ns, and the drain voltage detection pin VD of the synchronous rectifier chip U2 is connected to the second end of the secondary winding Ns through the output switch module 132; or

[0064] The output voltage detection pin VO of the synchronous rectifier chip U2 is connected to the output port 14 through the output switch module 132, the power secondary ground pin VSS_1 / 2 and the power positive pin VCC of the synchronous rectifier chip U2 are connected to the output port 14, the drain pin Drain_1 / 2 / 3 of the synchronous rectifier chip U2 is connected to the second end of the secondary winding Ns, and the drain voltage detection pin VD of the synchronous rectifier chip U2 is connected to the second end of the secondary winding Ns through the output switch module 132.

[0065] The synchronous rectifier chip U2 can monitor the voltage Vds between the D (drain) and S (source) of the first switching transistor M1 (using a MOS transistor as an example), detect whether Vds meets the conditions for the MOS transistor to be turned on or off, and if so, control the switching on or off. Furthermore, there is essentially no difference between whether the synchronous rectifier chip U2 is arranged on the high-voltage side or the low-voltage side of the secondary-side circuit 13; both are used to block the implementation of synchronous rectification. The implementation of synchronous rectification requires monitoring the voltage between the D and S pins and powering the synchronous rectifier chip U2. Both are indispensable, so blocking one path can shut down the first switching transistor M1.

[0066] In the above example, the drain of the MOS tube of the fifth switch tube Q1 is connected to the output port 14, and the source is connected to the drain voltage detection pin VD of the synchronous rectifier chip U2. This is to prevent the synchronous rectifier chip U2 from detecting the drain voltage of the first switch tube M1, thereby preventing synchronous rectification. The MOS tube of the fifth switch tube Q1 is connected in series between the output voltage detection pin VO of the synchronous rectifier chip U2 and the transformer T1 pin at one end of the secondary winding Ns. This is to prevent the synchronous rectifier chip U2 from detecting the source voltage of the first switch tube M1, thereby preventing synchronous rectification. The MOS tube of the fifth switch tube Q1 is connected in series between the positive power supply pin VCC of the synchronous rectifier chip U2 and the transformer T1 pin at one end of the secondary winding Ns. This is to block the power supply of the synchronous rectifier chip U2, thereby preventing synchronous rectification.

[0067] See also Figure 6 In some embodiments, the switching power supply circuit further includes a switch control module 16 , an input detection module 17 and an output detection module 18 .

[0068] The input detection module 17 is connected to the input port 11 and the switch control module 16 . The switch control module 16 is connected to the output switch module 132 . The input detection module 17 is configured to output a first driving voltage to the switch control module 16 when the input voltage Vin is greater than an input threshold.

[0069] The output detection module 18 is connected to the secondary side circuit 13 and the switch control module 16 . The output detection module 18 is configured to output a second driving voltage to the switch control module 16 when the output current Iout of the secondary side circuit 13 is greater than an output threshold.

[0070] The switch control module 16 is connected to the control end of the output switch module 132 and is configured to turn off the output switch module 132 when receiving the first driving voltage and the second driving voltage.

[0071] In this embodiment, the input voltage Vin and the output current Iout jointly determine the on / off switching of the output switch module 132. In other embodiments, only an overvoltage of the input voltage Vin or an overcurrent of the output current Iout, that is, only one of the first driving voltage and the second driving voltage, may be required to determine the on / off switching of the output switch module 132.

[0072] It is understood that the input detection module 17 stops outputting the first driving voltage if the input voltage Vin is not greater than the input threshold. The output detection module 18 stops outputting the second driving voltage to the switch control module 16 if the output current Iout is not greater than the output threshold. At this time, the switch control module 16 controls the output switch module 132 to conduct based on the output voltage of the output port 14.

[0073] See also Figure 7 In some embodiments, the switch control module 16 includes an on-control circuit 161 and an off-control circuit 162 .

[0074] The on-control circuit 161 is connected to the control end and the output port 14 of the output switch module 132, and is used to control the output switch module 132 to be turned on based on the output of the secondary side circuit 13; the off-control circuit 162 is connected to the control end, the input detection module 17 and the output detection module 18 of the output switch module 132, and is used to control the output switch module 132 to be turned off according to the first drive voltage and the second drive voltage.

[0075] When the switching power supply circuit is normal, the conduction control circuit 161 controls the output switch module 132 to be turned on based on the output of the secondary side circuit 13 and maintains the conduction until the switching power supply circuit becomes abnormal.

[0076] In the event of an abnormality in the switching power supply circuit, the shutdown control circuit 162 controls the output switch module 132 to be turned off according to the first driving voltage and / or the second driving voltage, thereby protecting the switching power supply circuit and its subsequent circuits.

[0077] See also Figure 8 In some embodiments, the conduction control circuit 161 includes a first resistor R34, a second resistor R35, a first diode D6, and a first capacitor C16;

[0078] A first end of the first resistor R34 is connected to the output port 14, a second end of the first resistor R34 is connected to the shutdown control circuit 162, and a first end of the second resistor R35 is connected to the anode of the first diode D6, and the cathode of the first diode D6 is connected to the control end of the output switch module 132. The first capacitor C16 is connected to the control end of the output switch module 132 and the shutdown control circuit 162.

[0079] The first resistor R34, the second resistor R35, and the first diode D6 form a startup circuit for the output switch module 132. When the switching power supply circuit is functioning normally, the output switch module 132 is controlled to conduct based on the output voltage of the output port 14. The first capacitor C16 serves as a power supply capacitor, maintaining a stable bias for the control terminal of the fifth switch transistor Q1 and providing protection therefor.

[0080] See also Figure 8 , in some embodiments, the shutdown control circuit 162 includes a first switch unit 1621 and a second switch unit 1622;

[0081] The first end of the first switch unit 1621 is connected to the control end of the output switch module 132, the second end of the first switch unit 1621 is connected to the first end of the second switch unit 1622, and the control end of the first switch unit 1621 is connected to the output detection module 18; the second end of the second switch unit 1622 is connected to the secondary ground of the power supply, and the control end of the second switch unit 1622 is connected to the input detection module 17.

[0082] In this embodiment, if the input and / or output of the switching power supply circuit are abnormal, the first switch unit 1621 and the second switch unit 1622 are turned on, pulling the gate voltage of the fifth switch transistor Q1 of the output switch module 132 to ground. This simultaneously discharges the first capacitor C16, thereby providing a reverse bias to the gate of the fifth switch transistor Q1, thereby turning it off. Subsequently, the synchronous rectifier chip U2 detects that synchronous rectification is unavailable and turns off the first switch transistor M1, allowing the first switch transistor M1 to freewheel through the body diode D0.

[0083] See also Figure 8 In some embodiments, the first switch unit 1621 includes a second switch tube Q2 and a third switch tube Q5. The first end of the second switch tube Q2 is connected to the conduction control circuit 161, the second end of the second switch tube Q2 is connected to the first end of the second switch unit 1622, and the control end of the second switch tube Q2 is connected to the output end of the output detection module 18; the first end of the third switch tube Q5 is connected to the control end of the output switch module 132, the second end of the third switch tube Q5 is connected to the first end of the second switch unit 1622, and the control end of the second switch tube Q2 is connected to the output end of the output detection module 18.

[0084] The second switch transistor Q2 and the third switch transistor Q5 can be semiconductor electronic tubes such as triodes or MOS tubes. Driven by the second driving voltage (i.e., the bias voltage), the second switch transistor Q2 and the third switch transistor Q5 are turned on, pulling the gate voltage of the fifth switch transistor Q1 down to ground, and simultaneously discharging the first capacitor C16.

[0085] In one embodiment, the first end of the second switch Q2 is connected to the second end of the first resistor R34, thereby turning off the fifth switch Q1 by lowering the input voltage Vin of the conduction control circuit 161. The first end of the third switch Q5 is connected to the gate of the fifth switch Q1 and one end of the first capacitor C16, thereby discharging the first capacitor C16 to ground. Together, the two provide a reverse bias for the gate of the fifth switch Q1, thereby turning it off.

[0086] It is understood that the first switch unit 1621 may include only the second switch tube Q2, with the first end of the second switch tube Q2 connected to both the conduction control circuit 161 and the control end of the output switch module 132. Turning on the second switch tube Q2 can simultaneously lower the input voltage Vin of the conduction control circuit 161 and discharge the first capacitor C16 to ground.

[0087] See also Figure 8 and Figure 9 In some embodiments, the second switch unit 1622 includes a photocoupler U3 and a fourth switch tube Q3. The input end of the light source of the photocoupler U3 is connected to the power supply V1, and the output end of the light source is connected to the first end of the fourth switch tube Q3. The input end of the light receiver of the photocoupler U3 serves as the first end of the second switch unit 1622, and the output end of the light receiver of the photocoupler U3 serves as the second end of the second switch unit 1622. The second end of the fourth switch tube Q3 is connected to the primary ground of the power supply, and the control end of the fourth switch tube Q3 serves as the control end of the second switch unit 1622.

[0088] See also Figure 9 In some embodiments, the input detection module 17 includes a voltage divider module 171 and a clamping module 172; the input end of the voltage divider module 171 is connected to the input port 11, the voltage divider output end of the voltage divider module 171 is connected to the input end of the clamping module 172, and the output end of the clamping module 172 is used to output the first driving voltage when the input voltage Vin is greater than the input threshold.

[0089] It is understood that the input (voltage) threshold is configured by the voltage divider module 171 and the clamp module 172. For example, the clamp module 172 includes a first voltage stabilizing diode ZD3, whose cathode and anode serve as the input and output terminals of the clamp module 172, respectively. The input threshold is then configured by the breakdown voltage of the first voltage stabilizing diode ZD3 and the voltage divider ratio of the voltage divider module 171.

[0090] In some embodiments, the voltage divider module 171 includes sequentially connected anti-backflow diodes D8 and D9, a voltage divider network R38, R39, and R40, and filter capacitors C17 and C18.

[0091] In some embodiments, a power supply circuit 19 is further included to provide power V1 for the optocoupler U3. The power supply circuit 19 includes a diode D10, a capacitor C19, a resistor R42, a switch Q4, a voltage regulator ZD4, and capacitors C20 and C21.

[0092] The anode of the diode D10 is connected to the input port 11, the cathode of the diode D10 is connected to the first end of the capacitor C19, the first end of the resistor R42 and the first end of the switch tube Q4, the second end of the capacitor C19 is connected to the primary ground of the power supply, the second end of the resistor R42 is connected to the control end of the switch tube Q4 and the cathode of the voltage regulator tube ZD4, the anode of the voltage regulator tube ZD4 is connected to the primary ground of the power supply, and the second end of the switch tube Q4 constitutes the output end of the power supply circuit 19. The capacitors C20 and C21 are connected between the output end of the power supply circuit 19 and the primary ground of the power supply. The output end of the power supply circuit 19 is connected to the input end of the light source of the optocoupler U3.

[0093] Exemplarily, the switch Q4 is an NPN transistor. When the input voltage Vin is higher than a threshold, the voltage regulator ZD4 turns on, pulling the control terminal of the switch Q4 low, turning it off, and thus shutting down the output of the power supply circuit 19. When the input voltage Vin is lower than the threshold, the voltage regulator ZD4 turns off, pulling the control terminal of the switch Q4 low, turning it off, and thus shutting down the output resistor R42 of the power supply circuit 19. Based on the input voltage Vin, the switch Q4 is biased and turned on, and the power supply circuit 19 then outputs the input voltage Vin.

[0094] In some embodiments, the output detection module 18 includes an operational amplifier U7, a second voltage stabilizing diode ZD2, and a detection resistor Rs. The first end of the detection resistor Rs is connected to the secondary winding Ns ( Figure 7 Shown is a second end connected to the secondary winding Ns) or the output port 14, the second end of the detection resistor Rs is connected to the secondary ground of the power supply, the negative input end of the operational amplifier U7 is connected to the first end of the detection resistor Rs, the positive input end of the operational amplifier U7 is connected to the secondary ground of the power supply, the output end of the operational amplifier U7 is connected to the cathode of the second voltage zener diode ZD2, and the anode of the second voltage zener diode ZD2 serves as the output end of the output detection module 18. The operational amplifier U7 is used to amplify the detection voltage Vsense formed based on the output current Iout loaded on the detection resistor Rs, and output the second drive voltage when the detection voltage is greater than the breakdown voltage of the second voltage zener diode ZD2.

[0095] Operational amplifier U7 is also connected to a power supply voltage. The reference voltage is provided by a power supply circuit comprising resistor R36, diode D7, and Zener diode ZD1. The anode of diode D7 is connected to output port 14 via resistor R36, the cathode of Zener diode ZD1 is connected to the cathode of diode D7, and the anode of Zener diode ZD1 is connected to the secondary ground of the power supply. The cathode of Zener diode ZD1 provides the supply voltage to the power supply terminal of operational amplifier U7.

[0096] In this embodiment, the output detection module 18 is used to control the second switch Q2 and the third switch Q5 of the first switch unit 1621. Therefore, the output detection module 18 includes two outputs, a voltage-limiting diode ZD5, and a current-limiting resistor R44. The output of the operational amplifier U7 is connected to the cathode of the voltage-limiting diode ZD5, and the anode of the voltage-limiting diode ZD5 is connected to the control terminal of the third switch Q5. The anode of the voltage-limiting diode is connected to the control terminal of the second switch Q2.

[0097] In other embodiments, the operational amplifier U7 and the second voltage-stabilizing diode ZD2 can be replaced by a comparison circuit.

[0098] In the switching power supply circuit, assuming that the turns ratio of the primary winding Np and the secondary winding Ns of the transformer T1 is N, the formula for calculating the reflected voltage is Vor = N (Vout + V M1 ), when short-circuited, Vout is essentially zero. At this point, the reflected voltage Vor depends on the voltage across the first switch tube M1. Taking a synchronous rectifier chip U2 as an example, assuming the on-resistance of the synchronous rectifier chip U2 is 10mΩ, and the output current Iout is transmitted by the main MOS tube of the first switch tube M1, when the overcurrent is 10A, V M1 =0.01*10=0.1V; Assuming that the body diode D0 of the first switch tube M1 is used for freewheeling, the voltage drop is the fixed conduction voltage drop of the body diode D0, V M1 =1.0V. It can be seen that the reflected voltage of the body diode D0 is 10 times that of the MOS tube.

[0099] Combine Figure 3 、 Figure 8 and Figure 9 In the flyback switching power supply circuit, the greater the reflected voltage, the shorter the demagnetization time required, the more demagnetization in the same working cycle, and the smaller the electrical stress of the main power switch. Detailed analysis process: From the volt-second balance formula, we can get V in *t on =V or *t off , where V in is the input voltage Vin; t on is the conduction time of the main power switch during the working cycle, that is, the charging time of the primary winding Np; toff is the off-time of the main power switch during the working cycle, that is, the discharge time of the secondary winding Ns. in =L*di / dt, L is the inductance of the winding. Discharge time t of the secondary winding Ns off is the demagnetization time t demag , the turns ratio of the primary and secondary windings Ns is N, and combining the above formulas, we can get t demag =L p* I p / N(Vout+V M1 ), I p =V cs / R0,N=N p / N s , I p The current of the main power switch, L p is the inductance of the primary winding, V cs is the threshold voltage of the current sampling pin CS of the switching power supply chip U1, N p 、N s are the turns of the primary and secondary windings respectively. demag The formula can be further processed to obtain: demag =L p* V cs* N s / N p* R 0* (Vout+V M1 ), from this analysis, we can know that the V M1 The larger the value, the less time is needed to demagnetize the magnet.

[0100] The above-described embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the various embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A switching power supply circuit, comprising an input port, a primary-side circuit, a transformer, a secondary-side circuit, and an output port connected in sequence, wherein the primary-side circuit includes a main power switch, a primary winding of the transformer, and the main power switch are connected between the input port and ground, characterized in that: The secondary side circuit includes a synchronous rectification module and an output switch module; the synchronous rectification module is connected between one end of the secondary winding of the transformer and the output port, the output switch module is connected between the synchronous rectification module and the secondary winding, or between the synchronous rectification module and the output port, the synchronous rectification module includes a first switch tube, and when the output switch module and the first switch tube are turned off, the body diode of the first switch tube is the output port for freewheeling, thereby increasing the reflected voltage coupled to the primary winding.

2. The switching power supply circuit according to claim 1, wherein: It also includes a switch control module, an input detection module and an output detection module; The input detection module is connected to the input port and the switch control module, and the switch control module is connected to the output switch module. The input detection module is configured to output a first driving voltage to the switch control module when the input voltage is greater than an input threshold; The output detection module is connected to the secondary side circuit and the switch control module, and the output detection module is used to output a second driving voltage to the switch control module when the output current of the secondary side circuit is greater than an output threshold; The switch control module is connected to the control end of the output switch module, and is configured to turn off the output switch module when receiving the first driving voltage and the second driving voltage.

3. The switching power supply circuit according to claim 2, wherein: The switch control module includes a conduction control circuit and a shutdown control circuit; The conduction control circuit is connected to the control terminal and the output port of the output switch module, and is used to control the conduction of the output switch module based on the output of the secondary side circuit; The shutdown control circuit is connected to the control end of the output switch module, the input detection module and the output detection module, and is used to control the output switch module to be turned off according to the first driving voltage and the second driving voltage.

4. The switching power supply circuit according to claim 3, wherein: The conduction control circuit includes a first resistor, a second resistor, a first diode, and a first capacitor; The first end of the first resistor is connected to the output port, the second end of the first resistor is connected to the shutdown control circuit and the first end of the second resistor, the second end of the second resistor is connected to the anode of the first diode, the cathode of the first diode is connected to the control end of the output switch module, and the first capacitor is connected to the control end of the output switch module and the shutdown control circuit.

5. The switching power supply circuit according to claim 3, wherein: The shutdown control circuit includes a first switch unit and a second switch unit; The first end of the first switch unit is connected to the control end of the output switch module, the second end of the first switch unit is connected to the first end of the second switch unit, and the control end of the first switch unit is connected to the output detection module; the second end of the second switch unit is connected to the secondary ground of the power supply, and the control end of the second switch unit is connected to the input detection module.

6. The switching power supply circuit according to any one of claims 2 to 5, characterized in that: The input detection module includes a voltage dividing module and a clamping module; The input end of the voltage divider module is connected to the input port, the voltage divider output end of the voltage divider module is connected to the input end of the clamp module, and the output end of the clamp module is used to output the first driving voltage when the input voltage is greater than the input threshold.

7. The switching power supply circuit according to any one of claims 2 to 5, wherein: The output detection module includes an operational amplifier, a second voltage-stabilizing diode, and a detection resistor. The first end of the detection resistor is connected to the secondary winding or the output port, the second end of the detection resistor is connected to the secondary ground of the power supply, the negative input end of the operational amplifier is connected to the first end of the detection resistor, the positive input end of the operational amplifier is connected to the secondary ground of the power supply, the output end of the operational amplifier is connected to the cathode of the second voltage-stabilizing diode, and the anode of the voltage-stabilizing diode serves as the output end of the output detection module. The operational amplifier is used to amplify the detection voltage formed based on the output current loaded on the detection resistor, and output the second drive voltage when the detection voltage is greater than the breakdown voltage of the second voltage-stabilizing diode.

8. The switching power supply circuit according to claim 5, wherein: The first switch unit includes a second switch tube and a third switch tube, wherein the first end of the second switch tube is connected to the conduction control circuit, the second end of the second switch tube is connected to the first end of the second switch unit, and the control end of the second switch tube is connected to the output end of the output detection module; the first end of the third switch tube is connected to the control end of the output switch module, the second end of the third switch tube is connected to the first end of the second switch unit, and the control end of the second switch tube is connected to the output end of the output detection module.

9. The switching power supply circuit according to claim 5 or 8, characterized in that: The second switch unit includes a photocoupler and a fourth switch tube. The input end of the light source of the photocoupler is connected to the power supply, and the output end of the light source is connected to the first end of the fourth switch tube. The input end of the light receiver of the photocoupler serves as the first end of the second switch unit, and the output end of the light receiver of the photocoupler serves as the second end of the second switch unit. The second end of the fourth switch tube is connected to the primary ground of the power supply, and the control end of the fourth switch tube serves as the control end of the second switch unit.

10. The switching power supply circuit according to any one of claims 1 to 5, characterized in that: The output switch module includes a fifth switch tube, and the control end of the fifth switch tube constitutes the control end of the output switch module; The fifth switch tube is connected between the synchronous rectification module and the output port; or The fifth switch tube is connected between the synchronous rectification module and the secondary winding.

11. The switching power supply circuit according to any one of claims 1 to 5, characterized in that: The synchronous rectification module includes a synchronous rectification chip, and the first switch tube is integrated with or externally mounted on the synchronous rectification chip; The positive power supply pin, the secondary power supply ground pin, and the output voltage detection pin of the synchronous rectifier chip are connected to the first end of the secondary winding, the drain pin of the synchronous rectifier chip is connected to the output port, and the drain voltage detection pin of the synchronous rectifier chip is connected to the output port through the output switch module; or The positive power pin of the synchronous rectifier chip is connected to the first end of the secondary winding through the output switch module, the secondary power ground pin and the output voltage detection pin of the synchronous rectifier chip are connected to the first end of the secondary winding, and the drain pin and the drain voltage detection pin of the synchronous rectifier chip are connected to the output port; or The positive power supply pin, the secondary power supply ground pin, and the output voltage detection pin of the synchronous rectifier chip are connected to the output port, the drain pin of the synchronous rectifier chip is connected to the second end of the secondary winding, and the drain voltage detection pin of the synchronous rectifier chip is connected to the second end of the secondary winding through the output switch module; or The positive power pin of the synchronous rectifier chip is connected to the output port through the output switch module, the secondary power ground pin and the output voltage detection pin of the synchronous rectifier chip are connected to the output port, the drain pin of the synchronous rectifier chip is connected to the second end of the secondary winding, and the drain voltage detection pin of the synchronous rectifier chip is connected to the second end of the secondary winding through the output switch module; or The output voltage detection pin of the synchronous rectifier chip is connected to the output port through the output switch module, the power secondary ground pin and the power positive pin of the synchronous rectifier chip are connected to the output port, the drain pin of the synchronous rectifier chip is connected to the second end of the secondary winding, and the drain voltage detection pin of the synchronous rectifier chip is connected to the second end of the secondary winding through the output switch module.

12. An electronic device, characterized in that: The method comprises the switching power supply circuit according to any one of claims 1 to 11.

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