Load current detection circuit and switching power supply

Abstract

The embodiment of the invention provides a load current detection circuit and a switching power supply, the load current detection circuit comprises a transformer, a secondary winding of the transformer is connected with an output circuit, and the output circuit is used for connecting a load; the rectification switch tube is connected in series in the output circuit; and the first controller is connected with the output circuit and the control end of the rectification switch tube, and is used for detecting the output voltage of the output circuit, detecting the switching period and the conduction time sequence of the rectification switch tube, and calculating the load current according to the output voltage, the switching period and the conduction time sequence. According to the load current detection circuit provided by the embodiment of the invention, the load current can be calculated according to the output voltage and the switching period and the conduction time sequence of the rectification switching tube, a sampling resistor does not need to be connected in series in an output circuit, power loss caused by the sampling resistor can be reduced, and the efficiency of a switching power supply can be improved.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to a load current detection circuit and a switching power supply. Background Technology

[0002] In flyback switching power supplies, a sampling resistor, such as an alloy resistor, is typically connected in series in the output circuit to detect the load current. Because the sampling resistor is connected in series in the output circuit, it causes some power loss.

[0003] For example, current fast charging power supplies have a maximum power output of around 120W and a maximum output current of 11A. The sampling resistor is typically a 5mΩ alloy resistor. According to the power calculation formula, the power loss through the sampling resistor is: 11A * 11A * 0.005Ω = 0.605W. This power loss has a significant impact on the overall power supply efficiency. Especially with the introduction of Level 7 energy efficiency standards, further improvements in power supply efficiency are required.

[0004] Therefore, how to solve the power loss caused by the sampling resistor in order to further improve power supply efficiency has become an urgent problem to be solved. Summary of the Invention

[0005] This application provides a load current detection circuit and a switching power supply, which can calculate the load current based on the output voltage, the switching cycle and conduction sequence of the rectifier switch, without the need for a sampling resistor in series in the output circuit, thereby reducing the power loss caused by the sampling resistor and improving the efficiency of the switching power supply.

[0006] This application provides a load current detection circuit for a switching power supply, including: A transformer, wherein the secondary winding of the transformer is connected to an output circuit, the output circuit being used to connect a load; The rectifier switch is connected in series in the output circuit; The first controller is connected to the control terminal of the output circuit and the rectifier switch, and is used to detect the output voltage of the output circuit, detect the switching period and conduction sequence of the rectifier switch, and calculate the load current based on the output voltage, the switching period and the conduction sequence.

[0007] In some embodiments, the first controller calculates the load current using the following formula: Wherein, Iout is the load current, Vout is the output voltage, Vf is the on-state voltage drop of the rectifier switch, Ls is the inductance of the secondary winding, T is the switching period of the rectifier switch, and Ton is the on-time of the rectifier switch.

[0008] In some embodiments, the load current detection circuit further includes a second controller connected to the control terminal of the rectifier switch, for outputting a drive signal to the control terminal to drive the rectifier switch to turn on or off; The first controller is used to detect the drive signal and obtain the switching period and the conduction timing.

[0009] In some embodiments, the load current detection circuit further includes an input switch and a third controller; The input switch is connected to the primary winding of the transformer and grounded. The control terminal of the input switch is connected to the third controller, which is used to control the input switch to be turned on or off.

[0010] In some embodiments, the first controller is connected to the third controller via a feedback circuit; The first controller is configured to: when the load current exceeds a current threshold, or the output power of the switching power supply exceeds a power threshold, or when the output voltage exceeds a voltage threshold, output a feedback signal to the third controller through the feedback circuit, so that the third controller controls the input switch to turn off.

[0011] In some embodiments, the first controller is configured to output the feedback signal to the third controller via the feedback circuit when the following relationship is satisfied: Where T is the switching period of the rectifier switch, Ton is the conduction timing of the rectifier switch, and K is a preset threshold.

[0012] In some embodiments, the load current detection circuit further includes an output switch transistor connected in series in the output circuit; The first controller is connected to the control terminal of the output switch and is used to control the output switch to be turned on or off.

[0013] In some embodiments, the first controller is configured to control the output switch to turn off when the following relationship is satisfied: Where T is the switching period of the rectifier switch, Ton is the conduction timing of the rectifier switch, and K is a preset threshold.

[0014] In some embodiments, the output circuit includes an output filter capacitor, one end of which is connected to one end of the secondary winding, and the other end of which is connected to the other end of the secondary winding.

[0015] This application also provides a switching power supply, including the load current detection circuit of any of the above embodiments.

[0016] The load current detection circuit of this application embodiment can calculate the load current based on the output voltage, the switching cycle and conduction sequence of the rectifier switch, without the need for a sampling resistor in series in the output circuit, which can reduce the power loss caused by the sampling resistor and thus improve the efficiency of the switching power supply. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0018] Figure 1 This is a schematic diagram of the load current detection circuit according to an embodiment of this application.

[0019] Figure 2 This is a structural example diagram of a load current detection circuit according to an embodiment of this application.

[0020] Figure 3 This is a waveform diagram of the drive signal of the rectifier switch in the load current detection circuit of this application embodiment.

[0021] Figure 4 This is a current waveform diagram of the secondary winding of the transformer in the load current detection circuit of this application embodiment. Detailed Implementation

[0022] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0023] This application provides a load current detection circuit and a switching power supply, which can calculate the load current based on the output voltage, the switching cycle and conduction sequence of the rectifier switch, without the need for a sampling resistor in series in the output circuit, thereby reducing the power loss caused by the sampling resistor and improving the efficiency of the switching power supply.

[0024] refer to Figure 1 , Figure 1This is a schematic diagram of the load current detection circuit 100 according to an embodiment of this application. The load current detection circuit 100 includes an input circuit 10, a transformer T1B, an output circuit 20, a rectifier switch 30, and a first controller 40.

[0025] Input circuit 10 is used to input power supply voltage. For example, in practical applications, input circuit 10 can be connected to an external AC power source to input an external AC voltage, such as 220V AC voltage.

[0026] Transformer T1B can be a flyback transformer. In this embodiment, the flyback transformer T1B operates in DCM mode (Discontinuous Conduction Mode, also known as intermittent conduction mode). Transformer T1B includes a primary winding NP and a secondary winding NS coupled together. The primary winding NP is connected to the input circuit 10, and the secondary winding NS is connected to the output circuit 20. The inductance of the secondary winding NS is Ls. The output circuit 20 is used to connect the load 101. Transformer T1B performs voltage conversion, transforming the input power supply voltage into the output voltage Vout required by the load 101, and the secondary winding NS provides the output voltage Vout to the load 101 via the output circuit 20. In practical applications, the output voltage Vout can include multiple voltage levels such as 5V, 9V, and 11V.

[0027] A rectifier switch 30 is connected in series in the output circuit 20. By turning the rectifier switch 30 on and off, the output circuit 20 can be controlled to be turned on or off, thereby rectifying the output voltage. The rectifier switch 30 is driven by a drive signal, such as a PWM drive signal, which can be represented as PWM1.

[0028] The first controller 40 is connected to the control terminals of the output circuit 20 and the rectifier switch 30. The first controller 40 is used to detect the output voltage Vout of the output circuit 20, and to detect the switching period T and the conduction timing Ton of the rectifier switch 30. Specifically, the first controller 40 can detect the drive signal PWM1 of the rectifier switch 30, and the switching period T and the conduction timing Ton can be obtained based on the high and low levels of the drive signal PWM1.

[0029] The first controller 40 is used to calculate the load current in the output circuit 20 based on the detected output voltage Vout, switching period T, and conduction timing Ton. The load current detection circuit of this embodiment will be further described in detail below with specific examples.

[0030] In some embodiments, reference Figure 2 , Figure 2This is a structural example diagram of a load current detection circuit according to an embodiment of this application.

[0031] The input circuit 10 includes a rectifier circuit BD1 and an input filter capacitor EC2. The rectifier circuit BD1 can be a bridge rectifier circuit composed of four diodes. The rectifier circuit BD1 includes four terminals 1, 2, 3, and 4. Terminal 1 is connected to the L (live) wire of the external AC power supply; terminal 2 is connected to the positive (+) terminal of the input filter capacitor EC2; terminal 3 is connected to the N (neutral) wire of the external AC power supply; and terminal 4 is connected to the negative terminal of the input filter capacitor EC2 and then connected to the ground terminal GND to achieve grounding.

[0032] The first terminal of the primary winding NP is connected to the positive (+) terminal of the input filter capacitor EC2. As mentioned above, the positive (+) terminal of the input filter capacitor EC2 is connected to the AC power supply through the rectifier circuit BD1, and the negative terminal of the input filter capacitor EC2 is connected to the rectifier circuit BD1 and grounded.

[0033] Output circuit 20 includes an output filter capacitor EC1. One end of output filter capacitor EC1 is connected to one end of the secondary winding NS, and the other end is connected to the other end of the secondary winding NS. For example, the positive (+) terminal of output filter capacitor EC1 is connected to one end of the secondary winding NS, and the negative (-) terminal of output filter capacitor EC1 is grounded, for example, connected to the ground terminal GND, and the negative (-) terminal is connected to the other end of the secondary winding NS, which can be understood as the grounded end, connected to the ground terminal GND. The voltage at the positive (+) terminal of output filter capacitor EC1 is the aforementioned output voltage Vout. Output filter capacitor EC1 is also connected to the output port of the switching power supply. The output port includes a voltage terminal V+ and a ground terminal GND. The voltage terminal V+ is connected to the positive (+) terminal of output filter capacitor EC1, and the ground terminal GND is connected to the negative (-) terminal of output filter capacitor EC1. The voltage terminal V+ and the ground terminal GND of the output port are used to provide the output voltage Vout. The load current in output circuit 20 is Iout.

[0034] The rectifier switch 30 is designated as switch Q1. Switch Q1 is connected in series between the ground terminal GND of the output port and the second terminal of the secondary winding NS. In some embodiments, switch Q1 is a MOSFET. The gate of switch Q1 is its control terminal, the source of switch Q1 is connected to the ground terminal GND of the output port, and the drain of switch Q1 is connected to the second terminal of the secondary winding NS.

[0035] The first controller 40 is denoted as U1. In some embodiments, the first controller U1 is a protocol chip. The protocol chip U1 includes a first sampling port Vout and a second sampling port GPIO. The first sampling port Vout is connected to the output circuit 20, for example, to the positive (+) terminal of the output filter capacitor EC1, or, as understood, to the voltage terminal V+ of the output port, to detect the output voltage Vout of the output circuit 20. The second sampling port GPIO is connected to the gate of the switching transistor Q1 to detect the drive signal PWM1 of the switching transistor Q1, and to obtain the switching period T and conduction timing Ton of the switching transistor Q1 based on the drive signal PWM1.

[0036] In some embodiments, such as Figure 2 As shown, the protocol chip U1 also includes a power supply port VCC, a sampling port CS-, a sampling port CS+, a control port Gate, a data port D-, a data port D+, a feedback port FB, and a ground port GND.

[0037] The power supply port VCC is connected to the output circuit 20, for example, to the positive (+) terminal of the output filter capacitor EC1. The output circuit 20 provides voltage Vout to the protocol chip U1, thus powering the protocol chip U1.

[0038] The output ports of the switching power supply are equipped with corresponding data ports D- and D+. The data port D- of the protocol chip U1 is connected to the data port D- of the output port, and the data port D+ of the protocol chip U1 is connected to the data port D+ of the output port to realize communication between the protocol chip U1 and the output port of the switching power supply.

[0039] Sampling ports CS- and CS+ can be left floating. The ground port GND should be grounded, for example, connected to the ground terminal GND. The functions of the control port Gate and the feedback port FB will be explained below.

[0040] In some embodiments, such as Figure 2 As shown, the load current detection circuit 100 also includes a second controller U2. In one example, the second controller U2 is a rectifier control chip. The second controller U2 is connected to the control terminal of the switching transistor Q1, for example, connected to the gate of the switching transistor Q1, and is used to output the aforementioned drive signal PWM1 to the gate of the switching transistor Q1 to drive the switching transistor Q1 to turn on or off.

[0041] The protocol chip U1 is connected to the gate of the switching transistor Q1, which can also be understood as being connected to the port where the second controller U2 outputs the drive signal PWM1. Therefore, the protocol chip U1 can be used to detect the drive signal PWM1 and obtain the switching period T and conduction timing Ton of the switching transistor Q1 based on the drive signal PWM1.

[0042] Please refer to the above. Figure 3 , Figure 3 This is a waveform diagram of the drive signal of the rectifier switch in the load current detection circuit of this application embodiment. The waveform of the drive signal PWM1 for switch Q1 is shown below. Figure 3 As shown. The drive signal PWM1 includes a high-level timing sequence and a low-level timing sequence within one period T. When the drive signal PWM1 is high, the drive switch Q1 is turned on, and the high-level timing sequence is the turn-on timing sequence Ton. When the drive signal PWM1 is low, the drive switch Q1 is turned off. Therefore, the protocol chip U1 can obtain the switching period T and the turn-on timing sequence Ton based on the high or low level of the drive signal PWM1.

[0043] In some embodiments, continue to refer to Figure 2 The second controller U2 includes a control port Gate, a ground port GND, and ports such as Rset, HV, VS, and VCC.

[0044] The control port Gate is connected to the gate of the switching transistor Q1 and also to the second sampling port GPIO of the protocol chip U1. The control port Gate is used to output the aforementioned drive signal PWM1.

[0045] The grounding port GND is connected to the grounding line of output circuit 20, for example, by connecting it to the negative (-) terminal of output filter capacitor EC1 to achieve grounding. The Rset port is connected to the grounding terminal GND through resistor R2. The Rset port is used to set the minimum on-time of the control port Gate of the second controller U2 to prevent malfunction of rectifier switch Q1. The HV port is connected to output circuit 20, for example, by connecting it to the positive (+) terminal of output filter capacitor EC1, providing voltage Vout to the second controller U2 through output circuit 20 to power the second controller U2. The VS port is connected to the grounded end of the transformer secondary winding NS through resistor R1. The VCC port is connected to the grounding terminal GND through capacitor C1.

[0046] In some embodiments, such as Figure 2 As shown, the load current detection circuit 100 also includes an output switch Q2. The output switch Q2 is connected in series in the output circuit 20, for example, between the positive (+) terminal of the output filter capacitor EC1 and the voltage terminal V+ of the output port. By turning the output switch Q2 on and off, the output circuit 20 can be controlled to be turned on or off. The control port Gate of the protocol chip U1 is connected to the control terminal of the output switch Q2, and is used to control the output switch Q2 to be turned on or off. When the output switch Q2 is on, the output circuit 20 is turned on; when the output switch Q2 is off, the output circuit 20 is turned off.

[0047] In some embodiments, the output switch Q2 is a MOSFET. The gate of the output switch Q2 is its control terminal. The source of the output switch Q2 is connected to the voltage terminal V+ of the output port, and the drain is connected to the positive (+) terminal of the output filter capacitor EC1.

[0048] In some embodiments, continue to refer to Figure 2 The load current detection circuit 100 also includes an input switch Q3 and a third controller U3. The input switch Q3 is connected to the primary winding NP of the transformer and grounded. The control terminal of the input switch Q3 is connected to the third controller U3. The third controller U3 is used to control the input switch Q3 to turn on or off. In practical applications, the third controller U3 can be a PWM controller, used to provide a drive signal PWM2 to the control terminal of the input switch Q3, thereby controlling the input switch Q3 to turn on or off.

[0049] Understandably, in practical applications, the input switch Q3 is the main switch of transformer T1B, used to control the input power or stop the input power of the primary winding NP of transformer T1B. Specifically, when the third controller U3 controls the input switch Q3 to be turned on, the primary winding NP of transformer T1B forms a circuit with ground through resistor R3, so the primary winding NP can input power and the secondary winding NS can output power; when the third controller U3 controls the input switch Q3 to be turned off, the primary winding NP of transformer T1B is disconnected from ground, so the primary winding NP stops inputting power and the secondary winding NS also stops outputting power. The third controller U3 can control the input power of the primary winding NP by adjusting the duty cycle of the drive signal PWM2, thereby controlling the output power of the secondary winding NS.

[0050] In some embodiments, the input switch Q3 is a MOSFET. In this case, the gate of the input switch Q3 is its control terminal. The gate of the input switch Q3 is connected to the third controller U3, the source is grounded (for example, the source can be connected to the ground terminal GND through resistor R3), and the drain is connected to the primary winding NP of the transformer.

[0051] In some embodiments, continue to refer to Figure 2 The first controller U1 (protocol chip U1) is connected to the third controller U3 via a feedback circuit. In one example, the feedback circuit may include an optocoupler comprising a light-emitting diode U3A and a phototransistor U3B coupled to each other. The anode of the light-emitting diode U3A is connected to the feedback port FB of the first controller U1, and its cathode is grounded, for example, connected to the ground port GND of the first controller U1. The emitter of the phototransistor U3B is grounded, and its collector is connected to the third controller U3.

[0052] Understandably, the first controller U1 can control the optocoupler to turn on or off through the feedback port FB, thereby adjusting the drive signal PWM2 output by the third controller U3 and thus achieving negative feedback control of the input switch Q3.

[0053] For example, in practical applications, the first controller U1 can be used to: when the calculated load current exceeds the current threshold, or the output power of the switching power supply exceeds the power threshold, or when the output voltage of the output circuit is detected to exceed the voltage threshold, output a feedback signal to the third controller U3 through the aforementioned feedback circuit, so that the third controller U3 controls the input switch Q3 to turn off. Specifically, the first controller U1 can control the feedback port FB to output a high level. At this time, the light-emitting diode U3A conducts and emits light, causing the phototransistor U3B to also conduct. As a result, the voltage at the port connected to the third controller U3 and the phototransistor U3B is pulled down to ground, i.e., a low level. The third controller U3 can then control the input switch Q3 to turn off based on this low-level signal.

[0054] The principle of the load current detection circuit in the embodiments of this application will be explained below.

[0055] First, it should be noted that, according to the law of electromagnetic induction, the magnetic flux Φ of an inductor coil and the current I satisfy the following relationship: Φ=L*I Where L is the inductance of the inductor coil, and the inductance L is an inherent parameter of the inductor coil.

[0056] According to the law of electromagnetic induction, the induced voltage ε across the inductor is equal to the rate of change of the magnetic flux Φ, which satisfies equation two: ε = ΔΦ / ΔT, where T represents time.

[0057] Combining relation one and relation two above, we can obtain the following relation three: ε=L*ΔI / ΔT Furthermore, we can obtain the following relation four: ΔI / ΔT=ε / L The basic operating process of a flyback transformer (such as transformer T1B in the embodiments of this application) is as follows: Process a, the primary winding of the transformer stores energy; then process b, the secondary winding of the transformer releases energy. These two processes do not occur simultaneously; in either process a or process b, the flyback transformer can be considered as an inductor. In process b, the induced voltage across the secondary winding of the flyback transformer is clamped at Vout + Vf, where Vout is the aforementioned output voltage, and Vf is the on-state voltage drop of the switching transistor Q1. Combining the above relationship four, the following relationship five can be obtained: Where Ls is the inductance of the secondary winding NS of transformer T1B, and Ls is an inherent parameter of the secondary winding NS, the value of which is fixed. Since the clamping voltage Vout+Vf is also fixed, the value of (Vout+Vf) / Ls is also fixed. Since process b releases the energy stored in process a, the energy of the transformer in process b gradually decreases, that is, the magnetic flux Φ gradually decreases. Therefore, according to Equation 1, the current in the secondary winding NS gradually decreases. Thus, ΔI / ΔT can be understood as the slope of the current decrease in the secondary winding NS, and this slope is a fixed value.

[0058] Please refer to the above. Figure 4 , Figure 4 This is a current waveform diagram of the transformer secondary winding in the load current detection circuit of this application embodiment. Where T represents the switching period of switch Q1, Ton represents the conduction sequence, and Is represents the maximum current of the secondary winding NS. For a flyback transformer operating in DCM mode, the current of the secondary winding NS will drop to 0 at the end of the conduction sequence Ton, therefore, the following relationship can be obtained: Combining relation five and relation six above, we can obtain the following relation seven: At the same time, by Figure 4 From the current change waveform diagram, the following relationship can be obtained: Where Iavg represents the average current over one switching cycle.

[0059] From the basic principle of flyback switching power supplies, we know that the output current Iout is equal to the average current Iavg over one switching cycle. Therefore, combining Equation 8 above, we can obtain the following Equation 9: By combining relation seven and relation nine above, we can obtain the following relation ten: Therefore, the first controller U1 can calculate the output current Iout according to the above relationship, and the output current Iout is the load current in the output circuit. Wherein, Vout is the output voltage of the output circuit, Vf is the on-state voltage drop of the switch Q1, Ls is the inductance of the secondary winding NS, T is the switching period of the switch Q1, and Ton is the on-time of the switch Q1.

[0060] The load current detection circuit of this application embodiment can calculate the load current Iout based on the output voltage Vout, the switching period T of the rectifier switch and the conduction sequence Ton. It eliminates the need for a sampling resistor in series in the output circuit, thereby reducing the power loss caused by the sampling resistor and improving the efficiency of the switching power supply.

[0061] Understandably, the clamping voltage Vout+Vf is a fixed value, and the inductance Ls of the secondary winding NS is also a fixed value. Therefore, in practical applications, the magnitude of the load current Iout depends on the value of the following expression: Therefore, for this expression, a preset threshold K can be set, and when the first controller U1 determines that the expression is satisfied... When the current exceeds the current threshold, it can be considered that the output current Iout exceeds the current threshold. At this time, the first controller U1 outputs a feedback signal to the third controller U3 through the feedback circuit, so that the third controller U3 controls the input switch Q3 to turn off, thereby realizing overcurrent protection, for example, limiting the output current Iout to within 8A.

[0062] Understandably, the output power of a switching power supply is calculated using the following formula: Therefore, based on the above analysis, the magnitude of the output power P also depends on the expression. The value. Therefore, when the first controller U1 determines that the condition is satisfied... This can also be considered as the output power exceeding the power threshold. At this time, the first controller U1 outputs a feedback signal to the third controller U3 through the feedback circuit, so that the third controller U3 controls the input switch Q3 to turn off, thereby realizing overload protection (OLP), for example, limiting the output power P to within 100W.

[0063] Understandably, based on the above analysis, the clamping voltage Vout+Vf is a fixed value. However, in practical applications, abnormal situations may occur, such as internal short circuits in the switching power supply or external interference, causing the output voltage Vout to rise abnormally. To address this, a voltage threshold can be preset. When the first controller U1 determines that the output voltage Vout exceeds the voltage threshold, the first controller U1 outputs a feedback signal to the third controller U3 through a feedback circuit, causing the third controller U3 to control the input switch Q3 to turn off, thereby achieving overvoltage protection (OVP), for example, limiting the output voltage Vout to below 30V.

[0064] In practical applications, the negative feedback control of the input switch Q3 by the first controller U1 may fail, for example, due to feedback circuit failure or external interference. Therefore, the output control of the switching power supply can be achieved through the output switch Q2.

[0065] Wherein, when the first controller U1 determines that the condition is satisfied When the output current Iout exceeds the current threshold, or the output power P exceeds the power threshold, the first controller U1 can output a low-level drive signal to the output switch Q2 through the control port Gate, thereby controlling the output switch Q2 to turn off, thus achieving overcurrent protection or overload protection.

[0066] In addition, when the first controller U1 determines that the output voltage Vout exceeds the voltage threshold, it can also control the output switch Q2 to turn off to achieve overvoltage protection.

[0067] Understandably, the first controller U1 can use negative feedback control to turn off the input switch Q3 to achieve overcurrent, overload, and overvoltage protection. It can also directly control the output switch Q2 to turn off for the same purposes. Therefore, this dual protection mechanism enhances the effectiveness of overcurrent, overload, and overvoltage protection. In the event of overcurrent, overload, or overvoltage, it promptly disconnects the power supply output, effectively protecting the power supply from damage.

[0068] This application also provides a switching power supply, including the load current detection circuit of any of the above embodiments. In practical applications, the switching power supply can be a flyback switching power supply.

[0069] In the description of this application, it should be understood that terms such as “first” and “second” are used only to distinguish similar objects and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated.

[0070] It should be noted that in the embodiments of this application, "connection" can be understood as electrical connection. The connection between two electrical components can be a direct or indirect connection between the two electrical components. For example, the connection between A and B can be a direct connection between A and B, or an indirect connection between A and B through one or more other electrical components.

[0071] The load current detection circuit and switching power supply provided in the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the embodiments above are only for the purpose of helping to understand this application. Furthermore, those skilled in the art will recognize that, based on the ideas of this application, there will be changes in the specific implementation methods and application scope. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A load current detection circuit for a switching power supply, characterized in that, include: A transformer, wherein the secondary winding of the transformer is connected to an output circuit, the output circuit being used to connect a load; The rectifier switch is connected in series in the output circuit; The first controller is connected to the control terminal of the output circuit and the rectifier switch, and is used to detect the output voltage of the output circuit, detect the switching period and conduction sequence of the rectifier switch, and calculate the load current based on the output voltage, the switching period and the conduction sequence.

2. The load current detection circuit according to claim 1, characterized in that, The first controller calculates the load current using the following formula: Wherein, Iout is the load current, Vout is the output voltage, Vf is the on-state voltage drop of the rectifier switch, Ls is the inductance of the secondary winding, T is the switching period of the rectifier switch, and Ton is the on-time of the rectifier switch.

3. The load current detection circuit according to claim 1, characterized in that, It also includes a second controller, which is connected to the control terminal of the rectifier switch, and is used to output a drive signal to the control terminal to drive the rectifier switch to turn on or off; The first controller is used to detect the drive signal and obtain the switching period and the conduction timing.

4. The load current detection circuit according to any one of claims 1 to 3, characterized in that, It also includes input switching transistors and a third controller; The input switch is connected to the primary winding of the transformer and grounded. The control terminal of the input switch is connected to the third controller, which is used to control the input switch to be turned on or off.

5. The load current detection circuit according to claim 4, characterized in that, The first controller is connected to the third controller via a feedback circuit; The first controller is configured to: when the load current exceeds a current threshold, or the output power of the switching power supply exceeds a power threshold, or when the output voltage exceeds a voltage threshold, output a feedback signal to the third controller through the feedback circuit, so that the third controller controls the input switch to turn off.

6. The load current detection circuit according to claim 5, characterized in that, The first controller is configured to output the feedback signal to the third controller via the feedback circuit when the following relationship is satisfied: Where T is the switching period of the rectifier switch, Ton is the conduction timing of the rectifier switch, and K is a preset threshold.

7. The load current detection circuit according to any one of claims 1 to 3, characterized in that, It also includes an output switch transistor, which is connected in series in the output circuit; The first controller is connected to the control terminal of the output switch and is used to control the output switch to be turned on or off.

8. The load current detection circuit according to claim 7, characterized in that, The first controller is configured to control the output switch to turn off when the following relationship is satisfied: Where T is the switching period of the rectifier switch, Ton is the conduction timing of the rectifier switch, and K is a preset threshold.

9. The load current detection circuit according to any one of claims 1 to 3, characterized in that, The output circuit includes an output filter capacitor, one end of which is connected to one end of the secondary winding, and the other end of which is connected to the other end of the secondary winding.

10. A switching power supply, characterized in that, Includes the load current detection circuit as described in any one of claims 1 to 9.

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