Backward flowing current detection circuit, forward topological structure and switching power supply
By introducing a reverse current detection circuit into the forward topology circuit, and utilizing the current signal sampling and detection unit and the bias unit, the problem of device failure during synchronous rectification is solved, thereby achieving device protection and lifespan extension.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SHENZHEN HONOR ELECTRONICS
- Filing Date
- 2025-12-29
- Publication Date
- 2026-05-05
AI Technical Summary
Existing forward topology circuits are prone to device failure during synchronous rectification, especially due to short circuits in the transformer secondary winding and reverse current from the output capacitor, which shorten device lifespan and cause failure.
A reverse current detection circuit is adopted, including a current signal sampling and detection unit and a bias unit. Through a circuit structure composed of current sensing devices, resistors and diodes, the existence of reverse current is detected and determined, and the branch of the target device is disconnected in time to protect the device.
This effectively avoids device failure, extends device lifespan, and enhances the anti-interference capability and reliability of reverse current detection.
Smart Images
Figure CN121978382A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of electronic circuit technology, specifically to a reverse current detection circuit, a forward topology, and a switching power supply. Background Technology
[0002] The forward topology circuit solves the problem of demagnetization of transformer cores through a magnetic reset mechanism, enabling efficient and reliable direct energy transfer.
[0003] In the prior art, the forward topology circuit of the switching power supply, such as Figure 1 As shown, the circuit includes a primary circuit, a transformer T, and a secondary circuit. The secondary circuit includes an inductor L and an output capacitor C1, which can be used for energy storage. During synchronous rectification, the main switch Q3 is on, the rectifier switch Q2 is on, and the freewheeling switch Q1 is off. During this process, component failures are prone to occur in the secondary circuit. Therefore, how to solve the component failure problem that occurs in the forward topology circuit during synchronous rectification has become an important issue that urgently needs to be addressed in this field. Summary of the Invention
[0004] To address the problems in the prior art, embodiments of this application provide a reverse current detection circuit, a forward topology, and a switching power supply, which can at least partially solve the problems existing in the prior art.
[0005] Firstly, this application proposes a reverse current detection circuit, including a current signal sampling and detection unit, wherein:
[0006] The current signal sampling and detection unit includes a current sensing device, a first resistor, a second resistor, a third resistor, and a first diode;
[0007] The primary side of the current sensing device is connected in series with the target device, the first resistor is connected in parallel with the secondary side of the current sensing device, the first end of the first resistor is connected to the anode of the first diode, the cathode of the first diode is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the second resistor, and the second end of the second resistor is grounded.
[0008] The second terminal of the third resistor outputs a first detection signal, which is used to compare with a first threshold to determine whether there is a reverse current flowing through the branch where the target device is located.
[0009] Furthermore, the reverse current detection circuit provided in this application embodiment also includes a bias unit, which is connected to the second end of the third resistor and is used to amplify the first detection signal to obtain a second detection signal. The second detection signal is used to compare with a second threshold to determine whether there is a reverse current flowing through the branch where the target device is located, so as to improve the anti-interference capability of the reverse current detection circuit.
[0010] Furthermore, the bias unit includes a fourth resistor, a fifth resistor, a sixth resistor, a second diode, and a first capacitor, wherein:
[0011] The first end of the sixth resistor is connected to the second end of the third resistor. The second end of the sixth resistor is connected to the first end of the fourth resistor, the first end of the fifth resistor, and the first end of the first capacitor. The second ends of the fourth resistor and the first capacitor are grounded. The second end of the fifth resistor is connected to the power supply voltage. The second end of the sixth resistor outputs a second detection signal.
[0012] Furthermore, the biasing unit also includes a second diode, the anode of which is connected to the second terminal of the sixth resistor, and the cathode of which is connected to the power supply voltage.
[0013] Furthermore, the second threshold is greater than or equal to K, which is calculated based on the supply voltage, the resistance value of the second resistor, the resistance value of the fourth resistor, the resistance value of the fifth resistor, and the resistance value of the sixth resistor.
[0014] Furthermore, the target device is a freewheeling switch in a rectifier circuit with a forward topology.
[0015] Secondly, this application provides a forward topology, including a transformer, a primary circuit, a rectifier circuit, and the reverse current detection circuit described in any of the above embodiments, wherein:
[0016] The transformer includes a primary winding and a secondary winding. The primary circuit is connected to the primary winding, and the rectifier circuit is connected to the secondary winding. The rectifier circuit includes a freewheeling switch, and the reverse current detection circuit is used to detect the reverse current in the branch where the freewheeling switch is located.
[0017] Furthermore, the rectifier circuit also includes a rectifier switch, an inductor, a third capacitor, and an output load resistor, wherein:
[0018] The rectifier switch and the freewheeling switch are connected in series and then connected in parallel with the secondary winding; the first terminal of the rectifier switch is connected to the first terminal of the secondary winding, and the second terminal of the rectifier switch is connected to the negative terminal.
[0019] The first end of the inductor is connected to the second end of the secondary winding, the second end of the inductor is connected to the positive terminal, the first end of the third capacitor and the first end of the output load resistor are connected to the positive terminal, and the second end of the third capacitor and the second end of the output load resistor are connected to the negative terminal.
[0020] Furthermore, the primary-side circuit includes a clamping switch, a clamping capacitor, a main switch, and a second capacitor, wherein:
[0021] The clamping switch and the clamping capacitor are connected in series and then connected in parallel with the primary winding;
[0022] The first end of the main switch is connected to the first end of the primary winding, the second end of the main switch is connected to the first end of the second capacitor, and the second end of the second capacitor is connected to the second end of the primary winding.
[0023] Thirdly, this application provides a switching power supply, including the forward topology and controller described in any of the above embodiments. The controller is connected to the control terminal of the freewheeling switch. The controller is used to turn off the freewheeling switch after determining, based on the detection signal provided by the reverse current detection circuit, that there is a reverse current flowing through the branch where the freewheeling switch is located.
[0024] The reverse current detection circuit, forward topology, and switching power supply provided in this application include a current signal sampling and detection unit. The current signal sampling and detection unit includes a current sensing device, a first resistor, a second resistor, a third resistor, and a first diode. The primary side of the current sensing device is connected in series with the target device. The first resistor is connected in parallel with the secondary side of the current sensing device. The first terminal of the first resistor is connected to the anode of the first diode, the cathode of the first diode is connected to the first terminal of the third resistor, the second terminal of the third resistor is connected to the first terminal of the second resistor, and the second terminal of the second resistor is grounded. The second terminal of the third resistor outputs a first detection signal, which is used to compare with a first threshold to determine whether a reverse current flows through the branch where the target device is located. Because it can detect in a timely manner whether a reverse current flows through the branch where the target device is located, it is beneficial to improve the service life of the devices in the branch and avoid device failure due to reverse current. Attached Figure Description
[0025] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. In the drawings:
[0026] Figure 1 This is a schematic diagram of the forward topology circuit of a switching power supply in the prior art.
[0027] Figure 2 This is a schematic diagram of current reverse current flowing into the forward topology circuit of a switching power supply in the prior art.
[0028] Figure 3This is a schematic diagram of the reverse current detection circuit provided in one embodiment of this application.
[0029] Figure 4 This is a schematic diagram of the reverse current detection circuit provided in another embodiment of this application.
[0030] Figure 5 This is a schematic diagram of the reverse current detection circuit provided in another embodiment of this application.
[0031] Figure 6 This is a schematic diagram of the reverse current detection circuit provided in another embodiment of this application.
[0032] Figure 7 This is a schematic diagram of a forward topology provided in an embodiment of this application.
[0033] Figure 8 This is a schematic diagram of a forward topology provided in another embodiment of this application.
[0034] Figure 9 This is a schematic diagram of the structure of a switching power supply provided in an embodiment of this application. Detailed Implementation
[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the embodiments of this application will be further described in detail below with reference to the accompanying drawings. Here, the illustrative embodiments and their descriptions are used to explain this application, but are not intended to limit this application. It should be noted that, unless otherwise specified, the embodiments and features in the embodiments of this application can be arbitrarily combined with each other. The acquisition, storage, use, and processing of data in the technical solutions of this application all comply with relevant laws and regulations. The user information in the embodiments of this application is obtained through legal and compliant means, and the acquisition, storage, use, and processing of user information have been authorized and agreed upon by the customer.
[0036] To facilitate understanding of the technical solution provided in this application, the relevant content of the technical solution in this application will be explained below.
[0037] like Figure 1 and Figure 2As shown, the forward topology circuit of the switching power supply includes a primary circuit, a transformer T, and a secondary circuit. The primary circuit includes a main switch Q3, a clamping switch Q4, a clamping capacitor C3, and an input capacitor C2. The secondary circuit includes a rectifier switch Q2, a freewheeling switch Q1, an inductor L, an output capacitor C1, and an output load resistor RO. DRV_CLM is the control terminal of the clamping switch Q4, DRV_MAIN is the control terminal of the main switch Q3, SR_A is the control terminal of the rectifier switch Q2, and SR_A is the control terminal of the freewheeling switch Q1. I1 and I2 are the current paths when reverse current occurs. When the primary circuit is powered, the freewheeling switch Q1 is turned off. The energy provided by the primary circuit stores energy in the inductor L, charges the output capacitor C1, and provides energy to the output load. Because the secondary circuit includes an inductor L for energy storage and an output capacitor C1, during synchronous rectification, if the primary side of the transformer does not transfer energy to the secondary side, and the main switch Q3 and rectifier switch Q2 are turned on while the freewheeling switch Q1 has not been turned off in time, the energy from the primary side of the transformer will cause a short circuit in the secondary winding of the transformer T through the current path I1, and the energy in the output capacitor C1 will be reverse-fed to the negative terminal AGND network of the output through the current path I2. This can easily cause a large current surge in the rectifier switch Q2 and the freewheeling switch Q1, resulting in a shortened lifespan of the devices or even device failure.
[0038] To address the aforementioned issues, this application proposes a reverse current detection circuit, including a current signal sampling and detection unit. The current signal sampling and detection unit is used to detect whether there is a reverse current flowing through the branch where the target device is located. When there is a reverse current flowing through, it can promptly provide a detection signal to the controller. The controller can promptly disconnect the branch where the target device is located to protect the device in the branch, improve the service life of the device in the branch, and avoid device failure due to reverse current.
[0039] Figure 3 This is a schematic diagram of the reverse current detection circuit provided in one embodiment of this application, as shown below. Figure 3 As shown, the reverse current detection circuit provided in this application embodiment includes a current signal sampling and detection unit, wherein:
[0040] The current signal sampling and detection unit includes a current sensing device, a first resistor R1, a second resistor R2, a third resistor R3, and a first diode D1;
[0041] The primary side CT-A of the current sensing device is connected in series with the target device Q1. The first resistor R1 is connected in parallel to the secondary side CT-B of the current sensing device. The first end of the first resistor R1 is connected to the anode of the first diode D1. The cathode of the first diode D1 is connected to the first end of the third resistor R3. The second end of the third resistor R3 is connected to the first end of the second resistor R2. The second end of the second resistor R2 is grounded.
[0042] The second terminal of the third resistor R3 outputs the first detection signal CCT. The first detection signal CCT is used to compare with the first threshold to determine whether there is reverse current flowing through the branch where the target device Q1 is located.
[0043] Specifically, the primary side CT-A of the current sensing device is connected in series in the branch where the target device Q1 is located. The primary side CT-A of the current sensing device senses the alternating current in the branch where the target device Q1 is located and generates an induced voltage signal. The secondary side CT-B of the current sensing device outputs a current sampling voltage. The first resistor R1 is connected in parallel in the secondary side CT-B of the current sensing device, and the second terminal of the first resistor R1 is grounded. The first resistor R1 serves as the load resistor for demagnetizing and resetting the current sensing device. When the first diode D1 is turned off, i.e., when there is no reverse current, the first resistor R1 releases the magnetically induced current in the secondary side CT-B of the current sensing device. When a reverse current occurs in the branch where the target device Q1 is located, the first diode D1 conducts, and the induced current in the secondary side CT-B of the current sensing device flows through the second resistor R2 and the third resistor R3. The second resistor R2 and the third resistor R3 serve as voltage divider resistors, and the second terminal of the third resistor R3 outputs the first detection signal CCT.
[0044] The first detection signal CCT is used to detect the reverse current of the target device Q1, specifically whether a reverse current flows through the branch containing the target device Q1. The first detection signal CCT is compared with a first threshold to determine whether a reverse current flows through the branch containing the target device Q1. When the first detection signal CCT is greater than or equal to the first threshold, it indicates that a reverse current flows through the branch containing the target device Q1; when the first detection signal CCT is less than the first threshold, it indicates that no reverse current flows through the branch containing the target device Q1. The second terminal of the third resistor R3 can be connected to the controller, providing the first detection signal CCT to the controller to determine whether a reverse current flows through the branch containing the target device Q1. The first threshold is set according to actual needs, and this embodiment does not limit its setting. In one embodiment, as shown... Figure 3 Therefore, when there is no reverse current, the end of the primary side CT-A of the current sensing device closest to the target device Q1 is the positive terminal. Figure 3 The symbol "+" indicates that the end furthest from the target device Q1 is the negative electrode. Figure 3 The symbol "-" indicates that when there is no reverse current, the end of the primary side CT-A of the current sensing device closest to the target device Q1 is the negative terminal. Figure 3 China and Israel This indicates that the end furthest from the target device Q1 is the positive electrode. Figure 3 The symbol ⊕ is used to represent the center.
[0045] In one embodiment, the second terminal of the third resistor R3 can be connected to a controller. After receiving the first detection signal CCT, the controller compares the first detection signal CCT with a first threshold. If the first detection signal CCT is greater than or equal to the first threshold, it indicates that there is reverse current flowing through the branch where the target device Q1 is located. The controller can then send a control signal to the control terminal SR_B of the target device Q1 to turn off the target device Q1, thereby disconnecting the branch where the target device Q1 is located. If the first detection signal CCT is less than the first threshold, it indicates that there is no reverse current flowing through the branch where the target device Q1 is located, and there is no need to disconnect the branch where the target device Q1 is located.
[0046] The reverse current detection circuit provided in this application includes a current signal sampling and detection unit, which includes a current sensing device, a first resistor, a second resistor, a third resistor, and a first diode. The primary side of the current sensing device is connected in series with the target device, the first resistor is connected in parallel with the secondary side of the current sensing device, the first end of the first resistor is connected to the anode of the first diode, the cathode of the first diode is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the second resistor, and the second end of the second resistor is grounded. The second end of the third resistor outputs a first detection signal, which is used to compare with a first threshold to determine whether there is a reverse current flowing through the branch where the target device is located. Since it can detect in a timely manner whether there is a reverse current flowing through the branch where the target device is located, it is beneficial to improve the service life of the devices in the branch and avoid device failure due to reverse current.
[0047] Figure 4 This is a schematic diagram of the reverse current detection circuit provided in another embodiment of this application, as shown below. Figure 4 As shown, based on the above embodiments, the reverse current detection circuit provided in this application further includes a bias unit 401, which is connected to the second end of the third resistor R3. The bias unit 401 is used to amplify the first detection signal CCT to obtain a second detection signal VCT. The second detection signal VCT is used to compare with a second threshold to determine whether there is a reverse current flowing through the branch where the target device Q1 is located, so as to improve the anti-interference capability of the reverse current detection circuit.
[0048] Specifically, when the reverse current in the branch containing the target device Q1 is small, the first detection signal CCT obtained by the current signal sampling and detection unit is small and easily affected by external interference. By adding a bias unit 401, the first detection signal CCT is amplified to obtain a second detection signal VCT. The second detection signal VCT is used to detect the reverse current of the target device Q1, detecting whether there is a reverse current flowing through the branch containing the target device Q1. The second detection signal VCT is compared with a second threshold to determine whether there is a reverse current flowing through the branch containing the target device Q1, thereby improving the anti-interference capability of the reverse current detection circuit. When the second detection signal VCT is greater than or equal to the second threshold, it indicates that there is a reverse current flowing through the branch containing the target device Q1; when the second detection signal VCT is less than the second threshold, it indicates that there is no reverse current flowing through the branch containing the target device Q1.
[0049] The output of the bias unit 401 can be connected to the controller to provide the second detection signal VCT to the controller to determine whether there is reverse current flowing through the branch where the target device Q1 is located. The second threshold can be set according to actual needs, and this embodiment does not limit its setting.
[0050] In one embodiment, the output of the bias unit 401 is connected to the controller. After receiving the second detection signal VCT, the controller compares the second detection signal VCT with a second threshold. If the second detection signal VCT is greater than or equal to the second threshold, it indicates that there is reverse current flowing through the branch where the target device Q1 is located. The controller can then send a control signal to the control terminal SR_B of the target device Q1 to turn off the target device Q1, thereby disconnecting the branch where the target device Q1 is located. If the second detection signal VCT is less than the second threshold, it indicates that there is no reverse current flowing through the branch where the target device Q1 is located, and there is no need to disconnect the branch where the target device Q1 is located.
[0051] This application embodiment reduces the occurrence of reverse current detection errors caused by external interference by adding a bias unit, thereby improving the reliability of the reverse current detection circuit.
[0052] Understandably, since the second detection signal VCT is more reliable than the first detection signal CCT, the second detection signal VCT is preferred for backflow current detection.
[0053] Figure 5 This is a schematic diagram of the reverse current detection circuit provided in another embodiment of this application, as shown below. Figure 5 As shown, based on the above embodiments, the reverse current detection circuit further includes a bias unit 401 and a current signal sampling and detection unit 402. The bias unit 401 includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a second diode D2, and a first capacitor C4, wherein:
[0054] The first end of the sixth resistor R6 is connected to the second end of the third resistor R3. The second end of the sixth resistor R6 is connected to the first end of the fourth resistor R4, the first end of the fifth resistor R5, and the first end of the first capacitor C4. The second ends of the fourth resistor R4 and the first capacitor C4 are grounded. The second end of the fifth resistor R5 is connected to the power supply voltage. The second end of the sixth resistor R6 outputs the second detection signal VCT.
[0055] Specifically, the sixth resistor R6 is connected in series with the first capacitor C4 to form an anti-interference circuit, improving the reliability of the bias unit 401. The second resistor R2 is connected in series with the sixth resistor R6, then in parallel with the fourth resistor R4, and finally in series with the fifth resistor R5 to form a voltage divider circuit. The second terminal of the fifth resistor R5 is connected to the power supply voltage, and the second terminal of the sixth resistor R6 outputs the second detection signal VCT. The second terminal of the sixth resistor R6 can be connected to the controller to provide the second detection signal VCT to the controller. The power supply voltage can be set according to actual needs, such as 3.3V or 5V; this embodiment does not limit the setting.
[0056] Figure 6 This is a schematic diagram of the reverse current detection circuit provided in another embodiment of this application, as shown below. Figure 6 As shown, based on the above embodiments, the bias unit 401 further includes a second diode D2, the anode of the second diode D2 is connected to the second terminal of the sixth resistor R6, and the cathode of the second diode D2 is connected to the power supply voltage.
[0057] Specifically, the second diode D2 is used for signal voltage clamping. Because a voltage is generated across the second resistor R2 and superimposed on the bias unit 401, the voltage of the current sensing device is raised. To prevent abnormal current signals from raising the voltage of the current sensing device to the controller's operating voltage, a second diode D2 is added. When the voltage at the input terminal of the second diode D2 is greater than the supply voltage, the second diode D2 conducts.
[0058] Based on the above embodiments, the second threshold is further greater than or equal to K, which is calculated based on the power supply voltage, the resistance value of the second resistor R2, the resistance value of the fourth resistor R4, the resistance value of the fifth resistor R5, and the resistance value of the sixth resistor R6.
[0059] In one embodiment, according to the formula K=V CC K and V are obtained by calculating [r4(r6+r2) / (r4+r6+r2)] / {[r4(r6+r2) / (r4+r6+r2)]+r5}. CC The supply voltage is represented by r4, the resistance value of the fourth resistor R4 is represented by r5, the resistance value of the fifth resistor R5 is represented by r2, and the resistance value of the second resistor R2 is represented by r6.
[0060] In one embodiment, V CC =3.3V, r4=200Ω, r6=200Ω, r5=1000Ω, r2=6.8Ω. According to the above formula, K=3.3×[200×(200+6.8) / (200+200+6.8)] / {[200×(200+6.8) / (200+200+6.8)]+1000}=0.305V.
[0061] Based on the above embodiments, the target device Q1 is further defined as a freewheeling switch in a forward topology rectifier circuit.
[0062] Figure 7 This is a schematic diagram of a forward topology provided in an embodiment of this application, as shown below. Figure 7 As shown, the forward topology provided in this application includes a transformer T, a primary-side circuit 701, a rectifier circuit 702, and a reverse current detection circuit 703 as described in any of the above embodiments, wherein:
[0063] The transformer T includes a primary winding TA and a secondary winding TB. The primary circuit 701 is connected to the primary winding TA, and the rectifier circuit 702 is connected to the secondary winding TB. The rectifier circuit 702 includes a freewheeling switch 7021, and a reverse current detection circuit 703 is used to detect the reverse current in the branch where the freewheeling switch 7021 is located.
[0064] Specifically, the freewheeling switch 7021 is the target device, and the reverse current detection circuit 703 detects the reverse current in the branch where the freewheeling switch 7021 is located. When a reverse current is detected flowing through the branch where the freewheeling switch 7021 is located, the controller promptly shuts off the freewheeling switch 7021 to reduce the impact of the reverse current on the device, extend the device's service life, and reduce the risk of device failure due to reverse current.
[0065] The forward topology provided in this application includes a transformer, a primary circuit, a rectifier circuit, and a reverse current detection circuit. The transformer includes a primary winding and a secondary winding. The primary circuit is connected to the primary winding, and the rectifier circuit is connected to the secondary winding. The rectifier circuit includes a freewheeling switch. The reverse current detection circuit is used to detect the reverse current in the branch where the freewheeling switch is located. By detecting the reverse current, it is beneficial to shut down the freewheeling switch in a timely manner, reduce the impact of reverse current on the devices, and improve the reliability of the forward topology.
[0066] Figure 8 This is a schematic diagram of a forward topology provided in another embodiment of this application, as shown below. Figure 8As shown, based on the above embodiments, the rectifier circuit 702 further includes a rectifier switch Q2, an inductor L, a third capacitor C1, and an output load resistor RO, wherein:
[0067] The rectifier switch Q2 and the freewheeling switch Q1 are connected in series and then in parallel with the secondary winding TB. The first terminal of the rectifier switch Q2 is connected to the first terminal of the secondary winding TB, and the second terminal of the rectifier switch Q2 is connected to the negative terminal. The second terminal of the rectifier switch Q2 is connected to the first terminal of the freewheeling switch Q1, and the second terminal of the freewheeling switch Q1 is connected to the second terminal of the secondary winding TB. A reverse current detection circuit 703 is set in the branch where the freewheeling switch Q1 is located.
[0068] The first end of the inductor L is connected to the second end of the secondary winding TB. The second end of the inductor L is connected to the positive terminal. The first end of the third capacitor C1 and the first end of the output load resistor RO are connected to the positive terminal. The second end of the third capacitor C1 and the second end of the output load resistor RO are connected to the negative terminal.
[0069] like Figure 8 As shown, based on the above embodiments, the primary-side circuit 701 further includes a clamping switch Q4, a clamping capacitor C3, a main switch Q3, and a second capacitor C2, wherein:
[0070] After clamping switch Q4 is connected in series with clamping capacitor C3, it is connected in parallel with primary winding TA;
[0071] The first terminal of the main switch Q3 is connected to the first terminal of the primary winding TA, the second terminal of the main switch Q3 is connected to the first terminal of the second capacitor C2, and the second terminal of the second capacitor C2 is connected to the second terminal of the primary winding TA.
[0072] In one embodiment, such as Figure 8 As shown, the forward topology provided in this application embodiment includes a transformer T, a primary-side circuit 701, a rectifier circuit 702, and a reverse current detection circuit 703, wherein:
[0073] The primary circuit 701 includes a clamping switch Q4, a clamping capacitor C3, a main switch Q3, and a second capacitor C2. The clamping switch Q4 and the clamping capacitor C3 are connected in series and then connected in parallel with the primary winding TA. The first end of the main switch Q3 is connected to the first end of the primary winding TA, the second end of the main switch Q3 is connected to the first end of the second capacitor C2, and the second end of the second capacitor C2 is connected to the second end of the primary winding TA.
[0074] The rectifier circuit 702 includes a freewheeling switch Q1, a rectifier switch Q2, an inductor L, a third capacitor C1, and an output load resistor RO. The rectifier switch Q2 and the freewheeling switch Q1 are connected in series and then in parallel with the secondary winding TB. The first terminal of the rectifier switch Q2 is connected to the first terminal of the secondary winding TB, and the second terminal of the rectifier switch Q2 is connected to the negative terminal. The second terminal of the rectifier switch Q2 is connected to the first terminal of the freewheeling switch Q1, and the second terminal of the freewheeling switch Q1 is connected to the second terminal of the secondary winding TB. The branch containing the freewheeling switch Q1 has a primary side CT-A of a current sensing device. The first terminal of the inductor L is connected to the second terminal of the secondary winding TB, and the second terminal of the inductor L is connected to the positive terminal. The first terminal of the third capacitor C1 and the first terminal of the output load resistor RO are connected to the positive terminal, and the second terminal of the third capacitor C1 and the second terminal of the output load resistor RO are connected to the negative terminal AGND.
[0075] The reverse current detection circuit 703 includes a current signal sampling and detection unit and a bias unit. The current signal sampling unit includes a current sensing device, a first resistor R1, a second resistor R2, a third resistor R3, and a first diode D1. The primary side CT-A of the current sensing device is connected in series with the freewheeling switch Q1. The first resistor R1 is connected in parallel to the secondary side CT-B of the current sensing device. The first end of the first resistor R1 is connected to the anode of the first diode D1, the cathode of the first diode D1 is connected to the first end of the third resistor R3, the second end of the third resistor R3 is connected to the first end of the second resistor R2, and the second end of the second resistor R2 is grounded. The bias unit includes a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a second diode D2, and a first capacitor C4. The first end of the sixth resistor R6 is connected to the second end of the third resistor R3. The second end of the sixth resistor R6 is connected to the first ends of the fourth resistor R4, the fifth resistor R5, and the first capacitor C4, respectively. The second ends of the fourth resistor R4 and the first capacitor C4 are grounded, and the second end of the fifth resistor R5 is connected to the power supply voltage. The second end of the sixth resistor R6 outputs a second detection signal VCT. The second detection signal VCT is used to detect the reverse current of the freewheeling switch Q1, checking whether there is a reverse current flowing through the branch where the freewheeling switch Q1 is located. The second detection signal VCT is compared with the second threshold to determine whether there is a reverse current flowing through the branch where the freewheeling switch Q1 is located, thereby improving the anti-interference capability of the reverse current detection circuit.
[0076] The control terminal DRV-CLM of clamp switch Q4 is connected to the controller, the control terminal DRV_MAIN of main switch Q3 is connected to the controller, the control terminal SR_B of freewheeling switch Q1 is connected to the controller, and the control terminal SR_A of rectifier switch Q2 is connected to the controller.
[0077] Figure 9 This is a schematic diagram of the structure of a switching power supply provided in an embodiment of this application, as shown below. Figure 9As shown, the switching power supply provided in this application embodiment includes the forward topology 900 and controller 1000 described in any of the above embodiments. The controller 1000 is connected to the control terminal of the freewheeling switch 9021. The controller 1000 is used to turn off the freewheeling switch 9021 after determining that there is a reverse current flowing through the branch where the freewheeling switch 9021 is located based on the detection signal provided by the reverse current detection circuit 903.
[0078] In one embodiment, the forward topology 900 includes a transformer T, a primary circuit 901, a rectifier circuit 902, and a reverse current detection circuit 903 as described in any of the above embodiments. The transformer T includes a primary winding TA and a secondary winding TB. The primary circuit 901 is connected to the primary winding TA, and the rectifier circuit 902 is connected to the secondary winding TB. The rectifier circuit 902 includes a freewheeling switch 9021. The reverse current detection circuit 903 is used to detect the reverse current in the branch where the freewheeling switch 9021 is located.
[0079] In one embodiment, the reverse current detection circuit 903 is structured as follows: Figure 3 As shown, the reverse current detection circuit 903 sends a first detection signal CCT to the controller 1000. The controller 1000 compares the first detection signal CCT with a first threshold. If the first detection signal CCT is greater than or equal to the first threshold, it indicates that there is a reverse current flowing through the branch where the freewheeling switch 9021 is located. The controller can then send a control signal to the control terminal of the freewheeling switch 9021 to turn off the freewheeling switch 9021, thereby disconnecting the branch where the freewheeling switch 9021 is located.
[0080] In one embodiment, the reverse current detection circuit 903 (the structure of the reverse current detection circuit 903 is as follows) Figure 5 or Figure 6 As shown, the second detection signal VCT is sent to the controller 1000. After receiving the second detection signal VCT, the controller 1000 compares the second detection signal VCT with the second threshold. If the second detection signal VCT is greater than or equal to the second threshold, it indicates that there is reverse current flowing through the branch where the freewheeling switch 9021 is located. The controller can send a control signal to the control terminal of the freewheeling switch 9021 to turn off the freewheeling switch 9021, thereby disconnecting the branch where the freewheeling switch 9021 is located.
[0081] In the description of this specification, the references to terms such as "an embodiment," "a specific embodiment," "some embodiments," "for example," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.
[0082] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of this application. It should be understood that the above descriptions are merely specific embodiments of this application and are not intended to limit the scope of protection of this application. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the scope of protection of this application.
Claims
1. A reverse current detection circuit, characterized in that, Includes a current signal sampling and detection unit, wherein: The current signal sampling and detection unit includes a current sensing device, a first resistor, a second resistor, a third resistor, and a first diode; The primary side of the current sensing device is connected in series with the target device, the first resistor is connected in parallel with the secondary side of the current sensing device, the first end of the first resistor is connected to the anode of the first diode, the cathode of the first diode is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the second resistor, and the second end of the second resistor is grounded. The second terminal of the third resistor outputs a first detection signal, which is used to compare with a first threshold to determine whether there is a reverse current flowing through the branch where the target device is located.
2. The reverse current detection circuit according to claim 1, characterized in that, It also includes a bias unit, which is connected to the second end of the third resistor and is used to amplify the first detection signal to obtain a second detection signal. The second detection signal is used to compare with a second threshold to determine whether there is a reverse current flowing through the branch where the target device is located, so as to improve the anti-interference capability of the reverse current detection circuit.
3. The reverse current detection circuit according to claim 2, characterized in that, The bias unit includes a fourth resistor, a fifth resistor, a sixth resistor, a second diode, and a first capacitor, wherein: The first end of the sixth resistor is connected to the second end of the third resistor. The second end of the sixth resistor is connected to the first end of the fourth resistor, the first end of the fifth resistor, and the first end of the first capacitor. The second ends of the fourth resistor and the first capacitor are grounded. The second end of the fifth resistor is connected to the power supply voltage. The second end of the sixth resistor outputs a second detection signal.
4. The reverse current detection circuit according to claim 3, characterized in that, The biasing unit further includes a second diode, the anode of which is connected to the second terminal of the sixth resistor, and the cathode of which is connected to the power supply voltage.
5. The reverse current detection circuit according to claim 3, characterized in that, The second threshold is greater than or equal to K, which is calculated based on the power supply voltage, the resistance value of the second resistor, the resistance value of the fourth resistor, the resistance value of the fifth resistor, and the resistance value of the sixth resistor.
6. The reverse current detection circuit according to any one of claims 1 to 5, characterized in that, The target device is a freewheeling switch in a forward topology rectifier circuit.
7. A forward topology, characterized in that, Includes a transformer, a primary circuit, a rectifier circuit, and a reverse current detection circuit as described in any one of claims 1 to 6, wherein: The transformer includes a primary winding and a secondary winding. The primary circuit is connected to the primary winding, and the rectifier circuit is connected to the secondary winding. The rectifier circuit includes a freewheeling switch, and the reverse current detection circuit is used to detect the reverse current in the branch where the freewheeling switch is located.
8. The forward topology according to claim 7, characterized in that, The rectifier circuit also includes a rectifier switch, an inductor, a third capacitor, and an output load resistor, wherein: The rectifier switch and the freewheeling switch are connected in series and then connected in parallel with the secondary winding; the first terminal of the rectifier switch is connected to the first terminal of the secondary winding, and the second terminal of the rectifier switch is connected to the negative terminal. The first end of the inductor is connected to the second end of the secondary winding, the second end of the inductor is connected to the positive terminal, the first end of the third capacitor and the first end of the output load resistor are connected to the positive terminal, and the second end of the third capacitor and the second end of the output load resistor are connected to the negative terminal.
9. The forward topology according to claim 7, characterized in that, The primary-side circuit includes a clamping switch, a clamping capacitor, a main switch, and a second capacitor, wherein: The clamping switch and the clamping capacitor are connected in series and then connected in parallel with the primary winding; The first end of the main switch is connected to the first end of the primary winding, the second end of the main switch is connected to the first end of the second capacitor, and the second end of the second capacitor is connected to the second end of the primary winding.
10. A switching power supply, characterized in that, The invention includes the forward topology and controller as described in any one of claims 7 to 9, wherein the controller is connected to the control terminal of the freewheeling switch, and the controller is used to turn off the freewheeling switch after determining, based on the detection signal provided by the reverse current detection circuit, that there is a reverse current flowing through the branch where the freewheeling switch is located.