Impedance adjusting circuit and switching power supply

Abstract

The embodiment of the utility model discloses an impedance adjusting circuit and a switching power supply, the impedance adjusting circuit comprises a conversion module and an impedance adjusting module, the conversion module is provided with a level input end and a first output end, when the level input end inputs a first level signal, the first output end outputs a first voltage, and when the level input end inputs a second level signal, the first output end outputs a second voltage. The first output end outputs a second voltage; the impedance adjusting module comprises a first impedance module and a second impedance module, the first impedance module is kept in a conducting state, the first end of the second impedance module is connected with the first end of the first impedance module, the second end of the second impedance module is connected with the second end of the first impedance module, and the controlled end of the second impedance module is connected with the first output end; when the first output end outputs the first voltage, the second impedance module is disconnected; when the first output end outputs the second voltage, the second impedance module is switched on. As the conversion module does not need to change the signal type, the conversion module can be composed of simple devices, and the circuit is relatively simple.

Description

Technical Field

[0001] This application relates to the field of switching power supply technology, and in particular to an impedance regulation circuit and a switching power supply. Background Technology

[0002] In a switching power supply, the voltage feedback pin receives a feedback signal from the output terminal, compares the actual output voltage value with the set value, and adjusts the pulse width of the switching transistor based on the comparison result. When the output voltage is lower than the set value, the voltage feedback pin sends a signal to the power management chip, causing it to increase the on-time of the switching transistor, thereby increasing the output voltage. Conversely, when the output voltage is higher than the set value, the voltage feedback pin reduces the on-time of the switching transistor to decrease the output voltage. Through continuous feedback and adjustment, the switching power supply can achieve a constant output voltage.

[0003] In related technologies, switching power supplies adjust the output voltage by adjusting the impedance of the feedback pin; however, circuits with adjustable impedance are usually quite complex. Utility Model Content

[0004] This application provides an impedance adjustment circuit and a switching power supply, which can make the circuit relatively simple.

[0005] In a first aspect, embodiments of this application provide an impedance adjustment circuit, comprising a conversion module and an impedance adjustment module. The conversion module has a level input terminal and a first output terminal. The level input terminal selectively inputs either a first level signal or a second level signal, wherein the magnitude or waveform of the first level signal and the second level signal are different. When the level input terminal inputs the first level signal, the first output terminal outputs a first voltage; when the level input terminal inputs the second level signal, the first output terminal outputs a second voltage. The impedance adjustment module comprises a first impedance module and a second impedance module. A first terminal of the first impedance module is used to connect to an external circuit, and a second terminal of the first impedance module is used to connect to an external circuit or ground. The first impedance module remains in a conducting state. The first terminal of the second impedance module is connected to the first terminal of the first impedance module, and the second terminal of the second impedance module is connected to the second terminal of the first impedance module. The controlled terminal of the second impedance module is connected to the first output terminal. When the first output terminal outputs the first voltage, the second impedance module is disconnected; when the first output terminal outputs the second voltage, the second impedance module is turned on.

[0006] Secondly, embodiments of this application provide a switching power supply, which includes an impedance adjustment circuit, a controller, and a voltage regulation module. The controller is connected to the level input terminal and is capable of outputting a first level signal or a second level signal. The voltage regulation module has a feedback pin, a first terminal of the first impedance module is connected to the feedback pin, and a second terminal of the first impedance module is grounded. The voltage regulation module is used to adjust the output voltage of the switching power supply according to the resistance of the impedance adjustment circuit.

[0007] Beneficial effects: The conversion module of this application converts a first level signal into a first voltage and a second level signal into a second voltage. The first voltage and the second voltage control the on / off state of the second impedance module, thereby adjusting the impedance of the impedance adjustment module. The conversion module does not need to change the signal type. Therefore, the conversion module can be composed of simple components, the circuit is relatively simple, and the cost is low. Attached Figure Description

[0008] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the embodiments 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.

[0009] Figure 1 This is a block diagram of an impedance adjustment circuit in one embodiment of this application;

[0010] Figure 2 This is a block diagram of an impedance adjustment circuit in another embodiment of this application;

[0011] Figure 3 This is a circuit diagram of an impedance adjustment circuit in one embodiment of this application;

[0012] Figure 4 This is a block diagram of an impedance adjustment circuit in another embodiment of this application;

[0013] Figure 5 This is a block diagram of the impedance adjustment circuit in another embodiment of this application;

[0014] Figure 6 This is a block diagram of an impedance adjustment circuit in another embodiment of this application;

[0015] Figure 7 This is a block diagram of a switching power supply in one embodiment of this application.

[0016] Explanation of reference numerals in the attached diagram: 100, Impedance adjustment circuit; 110, Conversion module; 111, Level input terminal; 112, First output terminal; 113, Second output terminal; 114, First voltage divider module; 115, Second voltage divider module; 120, Impedance adjustment module; 121, First impedance module; 122, Second impedance module; 123, Third impedance module; 130, First delay module; 140, Second delay module; 150, Isolation module; R1, First resistor; R2, Second resistor; R3, Third resistor; R4, First voltage divider resistor; R5, Second voltage divider resistor; Q1, First switching transistor; Q2, Second switching transistor; C1, Filter capacitor; ZD1, Zener diode; D1, Discharge diode; 200, Switching power supply; 210, Controller; 220, Voltage regulation module. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0018] like Figure 1 As shown, the first aspect of this application provides an impedance adjustment circuit 100, which is suitable for circuits that require different impedances, such as when the impedance adjustment circuit 100 is applied to a switching power supply to adjust the voltage or current of the switching power supply.

[0019] The impedance adjustment circuit 100 includes a conversion module 110 and an impedance adjustment module 120.

[0020] The impedance adjustment module 120 includes a first impedance module 121 and a second impedance module 122. A first terminal of the first impedance module 121 is used to connect to an external circuit, and a second terminal of the first impedance module 121 is used to connect to an external circuit or ground. For example, the impedance adjustment module 120 can be positioned between two external circuits, or between an external circuit and ground. The first impedance module 121 remains in a conducting state, meaning it is not controlled by the conversion module 110. Regardless of the signal input to the level input terminal 111, the impedance adjustment module 120 at least has the impedance provided by the first impedance module 121. The impedance of the first impedance module 121 is typically one of the impedances required by the impedance adjustment circuit 100. When the impedance of the impedance adjustment circuit 100 is the impedance of the first impedance module 121, other modules of the impedance adjustment circuit 100 do not need to operate, thereby saving power.

[0021] The first end of the second impedance module 122 is connected to the first end of the first impedance module 121, the second end of the second impedance module 122 is connected to the second end of the first impedance module 121, and the controlled end of the second impedance module 122 is connected to the first output end 112.

[0022] The conversion module 110 is used to adjust the impedance of the impedance adjustment module 120 to a desired value. The conversion module 110 has a level input terminal 111 and a first output terminal 112. The level input terminal 111 selectively inputs either a first level signal or a second level signal. The first level signal can, exemplarily, be a fixed level or a fluctuating level, and the second level signal can, exemplarily, be a fixed level or a fluctuating level. It should be noted that a fixed level includes multiple levels of different high and low values, and a fluctuating level includes multiple levels of different fluctuation amplitudes or frequencies. The first level signal and the second level signal are different.

[0023] Depending on the signal input to the level input terminal 111, the first output terminal 112 outputs at least two voltage levels. These at least two voltage levels control the on / off state of the second impedance module 122, thereby adjusting the impedance of the impedance adjustment module 120. For example, when a first level signal is input to the level input terminal 111, the first output terminal 112 outputs a first voltage; when a second level signal is input to the level input terminal 111, the first output terminal 112 outputs a second voltage. It is understood that the first or second level signal is itself a voltage signal; therefore, the conversion module 110 does not need to convert the signal type. That is, the conversion module 110 can be composed of simple components such as resistors and capacitors without the need for a control chip, thus making the conversion module 110 simple in structure and low in cost.

[0024] When a first level signal is input to the level input terminal 111, the first output terminal 112 outputs a first voltage. The conversion module 110 controls the second impedance module 122 to disconnect through the first output terminal 112, at which time the first impedance module 121 independently provides impedance. When a second level signal is input to the level input terminal 111, the first output terminal 112 outputs a second voltage. The conversion module 110 controls the second impedance module 122 to conduct through the first output terminal 112, at which time the first impedance module 121 and the second impedance module 122 are connected in parallel and jointly provide impedance. For example, a switch can be provided in the second impedance module 122. By turning the switch on or off through the first output terminal 112 of the conversion module 110, the connection of the second impedance module 122 in parallel with the first impedance module 121 can be controlled. The switch can, for example, be a diode, transistor, field-effect transistor, IGBT, thyristor, optocoupler, etc.

[0025] The conversion module 110 of this application converts a first level signal into a first voltage and a second level signal into a second voltage. It controls the on / off state of the second impedance module 122 by using the first voltage and the second voltage, thereby adjusting the impedance of the impedance adjustment module 120. The conversion module 110 does not need to change the signal type. Therefore, the conversion module 110 can be composed of simple components, resulting in fewer components in the impedance adjustment circuit, smaller circuit board space, simpler and more reliable circuit, easier debugging, and lower cost.

[0026] like Figure 2 As shown, in some embodiments, the impedance adjustment module 120 further includes a third impedance module 123, the first end of the third impedance module 123 is connected to the first end of the first impedance module 121, the second end of the third impedance module 123 is connected to the second end of the first impedance module 121, and the controlled end of the third impedance module 123 is connected to the second output end 113.

[0027] The level input terminal 111 can selectively input a first level signal, a second level signal, or a third level signal, wherein the third level signal is different from the first level signal and also different from the second level signal. The third level signal can be, for example, a fixed level or a fluctuating level.

[0028] The conversion module 110 also has a second output terminal 113. Depending on the signal input to the level input terminal 111, the second output terminal 113 outputs at least two levels of voltage, thereby controlling the on / off state of the third impedance module 123 to adjust the impedance of the impedance adjustment module 120.

[0029] For example, when a first level signal is input to the level input terminal 111, the second output terminal 113 outputs a third voltage; when a second level signal is input to the level input terminal 111, the second output terminal 113 outputs a fourth voltage; when a third level signal is input to the level input terminal 111, the first output terminal 112 outputs a second voltage, and the second output terminal 113 outputs either a third voltage or a fifth voltage. Both the third voltage and the fifth voltage can disconnect the third impedance module 123. It is understood that the third impedance module 123 can be disconnected by multiple voltages. Therefore, when a third level signal is input to the level input terminal 111, the second output terminal 113 can output either the third voltage or a fifth voltage different from the third voltage.

[0030] When a first level signal is input to the level input terminal 111, the first output terminal 112 outputs a first voltage. The conversion module 110 controls the second impedance module 122 to disconnect through the first output terminal 112, and the second output terminal 113 outputs a third voltage. The conversion module 110 controls the third impedance module 123 to disconnect through the second output terminal 113. At this time, the first impedance module 121 independently provides impedance. The first voltage and the third voltage can be the same or different.

[0031] When a second level signal is input to the level input terminal 111, the first output terminal 112 outputs a second voltage. The conversion module 110 controls the second impedance module 122 to conduct through the first output terminal 112, and the second output terminal 113 outputs a fourth voltage. The conversion module 110 also controls the third impedance module 123 to conduct through the second output terminal 113. At this time, the first impedance module 121, the second impedance module 122, and the third impedance module 123 are connected in parallel to provide impedance. The second voltage and the fourth voltage can be the same or different.

[0032] It is understood that the second impedance module 122 can have multiple conduction voltages. For example, the second impedance module 122 can have a second voltage or a fifth voltage, and the second voltage and the fifth voltage are different. When a third level signal is input to the level input terminal 111, the first output terminal 112 outputs the second voltage or the fifth voltage, and the conversion module 110 controls the second impedance module 122 to conduct through the first output terminal 112.

[0033] It is also understandable that the third impedance module 123 can have multiple conduction voltages. For example, the third impedance module 123 can have a third voltage or a sixth voltage, and the third voltage and the sixth voltage are different. When the level input terminal 111 inputs a third level signal, the second output terminal 113 outputs a third voltage or a sixth voltage. The conversion module 110 controls the third impedance module 123 to disconnect through the second output terminal 113. At this time, the first impedance module 121 and the second impedance module 122 are connected in parallel to provide impedance together.

[0034] In this embodiment, the impedance adjustment module 120 has three impedance levels, and the required impedance level can be selected according to the needs.

[0035] In other embodiments, the impedance adjustment module 120 further includes multiple impedance modules, thereby providing multiple impedance adjustment levels. Exemplarily, the impedance adjustment module 120 also includes a fourth impedance module, with a first terminal connected to a first terminal of the first impedance module 121 and a second terminal connected to a second terminal of the first impedance module 121. The conversion module 110 also has a third output terminal that outputs at least two voltage levels to control the switching of the fourth impedance module, thereby adjusting the impedance of the impedance adjustment module 120.

[0036] like Figure 3As shown, in some embodiments, the first impedance module 121 includes a first resistor R1. A first terminal of the first resistor R1 is used to connect to an external circuit, and a second terminal of the first resistor R1 is grounded. By providing impedance through the first resistor R1, the number of components in the first impedance module 121 is reduced, resulting in lower cost and less space occupied on the circuit board. It is understood that the first impedance module 121 may also include multiple resistors, which can be connected in series, parallel, or a combination thereof to combine conventional resistors to achieve different resistance values.

[0037] The second impedance module 122 includes a second resistor R2 and a first switch Q1. The first end of the second resistor R2 is connected to the first end of the first resistor R1, and the second end of the second resistor R2 is connected to the input terminal of the first switch Q1. The output terminal of the first switch Q1 is grounded, and the controlled terminal of the first switch Q1 is connected to the first output terminal 112. The first switch Q1 can be, for example, a MOSFET, a transistor, etc. The second impedance module 122 can be switched on and off using a single resistor and a single switch. Because the second impedance module 122 has a small number of components, its cost is low, and it occupies less space on the circuit board. It is understood that the second impedance module 122 can also include multiple resistors and multiple switches. Multiple resistors can be connected in series, parallel, or a combination thereof to create different resistance values. Multiple switches can be connected in series to further improve the isolation effect.

[0038] The third impedance module 123 includes a third resistor R3 and a second switch Q2. The first end of the third resistor R3 is connected to the first end of the first resistor R1, and the second end of the third resistor R3 is connected to the input terminal of the second switch Q2. The output terminal of the second switch Q2 is grounded, and the controlled terminal of the second switch Q2 is connected to the second output terminal 113. The second switch Q2 can be, for example, a MOSFET or a transistor. The third impedance module 123 can be switched on and off using a single resistor and a single switch. Because the number of components in the third impedance module 123 is relatively small, the cost is low, and it occupies less space on the circuit board. It is understood that the third impedance module 123 can also include multiple resistors and multiple switches. Multiple resistors can be connected in series, parallel, or a combination thereof to create different resistance values. Multiple switches can be connected in series to further improve the isolation effect.

[0039] like Figure 4As shown, in some embodiments, the conversion module 110 includes a first voltage divider module 114 and a second voltage divider module 115. The first terminal of the first voltage divider module 114 is connected to the level input terminal 111 and the first output terminal 112, and the second terminal of the first voltage divider module 114 is grounded. The first voltage divider module 114 is used to divide the voltage of the level input terminal 111, thereby providing the required voltage to the first output terminal 112.

[0040] The first terminal of the second voltage divider module 115 is connected to the first terminal of the first voltage divider module 114, the second terminal of the second voltage divider module 115 is connected to the second terminal of the first voltage divider module 114, and the third terminal of the second voltage divider module 115 is connected to the second output terminal 113. Based on the voltage division by the first voltage divider module 114, the second voltage divider module 115 divides the voltage at the first output terminal 112, thereby providing the required voltage to the second output terminal 113.

[0041] By using two voltage divider modules, the first output terminal 112 and the second output terminal 113 can output different or the same voltage.

[0042] In some embodiments, the first voltage divider module 114 has a voltage dividing effect on steady DC power, the second voltage divider module 115 has a voltage dividing effect on fluctuating DC power, the first level signal and the second level signal can be stable level signals, and the third level signal can be a fluctuating level signal.

[0043] When a first-level signal is input to the signal input terminal, the second voltage divider module 115 does not perform voltage division, and the first output terminal 112 and the second output terminal 113 output the same voltage, thereby causing the second impedance module 122 and the third impedance module 123 to be disconnected. For example, the first-level signal is a low-level signal, at which time the first voltage is 0 volts and the third voltage is 0 volts.

[0044] When a second-level signal is input to the signal input terminal, the second voltage divider module 115 does not perform voltage division, and the first output terminal 112 and the second output terminal 113 output the same voltage, thereby causing the second impedance module 122 and the third impedance module 123 to be disconnected. For example, the second-level signal is a high-level signal, at which time the first voltage is 7.5 volts and the third voltage is 7.5 volts.

[0045] When a third-level signal is input to the signal input terminal, the second voltage divider module 115 performs voltage division, resulting in different voltages output from the first output terminal 112 and the second output terminal 113. This causes the second impedance module 122 to conduct and the third impedance module 123 to deactivate. For example, the third-level signal is a square wave signal. The second voltage divider module 115 includes a filter module. When a square wave signal is input to the level input terminal 111, the filter module divides the square wave signal to make the third voltage lower than the fourth voltage, or the sixth voltage lower than the fourth voltage, thus preventing the second impedance module from reaching its conduction voltage. For example, the fourth voltage is 7.5 volts, the third voltage is 0 volts, and the sixth voltage is 5 volts. The frequency of the square wave signal can, for example, be 1 kHz, and the duty cycle can, for example, be 50%.

[0046] It is understandable that high-level, low-level, and square wave signals are all relatively common signals in switching power supplies. Therefore, there is no need to add special components to generate high-level, low-level, and square wave signals, thereby reducing circuit complexity and saving costs. It should be noted that the duty cycle and voltage value of the square wave signal can be adjusted. By inputting square wave signals of different waveforms, the voltage at the third output terminal can be adjusted. Furthermore, in this embodiment, the specifications of the second impedance module 122 and the third impedance module 123 can be the same to save costs.

[0047] like Figure 3 As shown, in some embodiments, the first voltage divider module 114 includes a first voltage divider resistor R4. The first end of the first voltage divider resistor R4 is connected to the level input terminal 111 and the first output terminal 112, and the second end of the first voltage divider resistor R4 is grounded. By using the first voltage divider resistor R4 for voltage division, the number of components in the first voltage divider module 114 is reduced, resulting in lower cost and less space occupied on the circuit board. It is understood that the first voltage divider module 114 may also include multiple voltage divider resistors, which can be connected in series, parallel, or a mixed configuration to achieve the voltage value obtained by voltage division using conventional resistors.

[0048] The second voltage divider module 115 includes a second voltage divider resistor R5 and a filter capacitor C1. The first end of the second voltage divider resistor R5 is connected to the first end of the first voltage divider resistor R4. The second end of the second voltage divider resistor R5 is connected to the second output terminal 113 and the first end of the filter capacitor C1. The second end of the filter capacitor C1 is connected to the second end of the first voltage divider resistor R4. By forming an RC filter circuit with a single resistor and capacitor, the second voltage divider module 115 achieves the effect of passing high frequencies and blocking low frequencies.

[0049] like Figure 3As shown, in some embodiments, the second voltage divider module 115 further includes a Zener diode ZD1. The positive terminal of the Zener diode ZD1 is connected to the second terminal of the second voltage divider resistor R5, and the negative terminal of the Zener diode ZD1 is connected to the second output terminal 113. When a square wave signal is input to the signal input terminal, although the second voltage divider module 115 performs voltage division, the voltage at the third terminal of the second voltage divider module 115 is still greater than zero, that is, the voltage at the second output terminal 113 is greater than zero. By setting the Zener diode ZD1, the forward voltage of the Zener diode ZD1 is greater than the voltage at the third terminal of the second voltage divider module 115 at this time, that is, the forward voltage of the Zener diode ZD1 is greater than the voltage at the second terminal of the voltage divider resistor. The Zener diode ZD1 cannot be turned on, that is, the Zener diode ZD1 can play a cutoff role, thereby making the voltage at the second output terminal 113 zero, so as to further reduce the probability of the second impedance module 122 being mis-turned on.

[0050] like Figure 3 As shown, in some embodiments, the second voltage divider module 115 further includes a discharge diode D1. The positive terminal of the discharge diode D1 is connected to the first terminal of the second voltage divider resistor R5, and the negative terminal of the discharge diode D1 is connected to the second terminal of the second voltage divider resistor R5. The discharge diode D1 can accelerate the discharge speed of the filter capacitor C1, resulting in better filtering performance.

[0051] like Figure 5 As shown, in some embodiments, the adjustment circuit further includes a first delay module 130 and a second delay module 140. The first end of the first delay module 130 is connected to the first output terminal 112, and the second end of the first delay module 130 is grounded.

[0052] The first terminal of the second delay module 140 is connected to the second output terminal 113, and the second terminal of the first delay module 130 is grounded. The first delay module 130 allows the second impedance module 122 to conduct with a delay after the first output terminal 112 reaches the second voltage for a certain period, and to deactivate with a delay after the first output terminal 112 falls below the second voltage for a certain period. In other words, the first delay module 130 provides a certain degree of anti-interference, making the state of the second impedance module 122 more stable and reducing the probability of malfunction. Similarly, the second delay module 140 allows the third impedance module 123 to conduct with a delay after the second output terminal 113 reaches the fourth voltage for a certain period, and to deactivate with a delay after the second output terminal 113 falls below the fourth voltage for a certain period. In other words, the second delay module 140 provides a certain degree of anti-interference, making the state of the third impedance module 123 more stable and reducing the probability of malfunction.

[0053] For example, such as Figure 3As shown, the first delay module 130 includes a resistor R6 and a capacitor C2. The resistor R6 and capacitor C2 are connected in parallel between the gate and source of the MOSFET Q1 to generate an RC delay, thereby reducing inrush current and slowing down the switching speed of the MOSFET Q1. The second delay module 140 includes a resistor R7 and a capacitor C3. The resistor R7 and capacitor C3 are connected in parallel between the gate and source of the MOSFET Q2 to generate an RC delay, thereby reducing inrush current and slowing down the switching speed of the MOSFET Q2.

[0054] like Figure 6 As shown, in some embodiments, the impedance adjustment circuit 100 further includes an isolation module 150. The input terminal of the isolation module 150 is used to selectively input a fourth level signal, a fifth level signal, and a sixth level signal. The output terminal of the isolation module 150 is connected to the level input terminal 111. When the fourth level signal is input to the input terminal of the isolation module 150, the output terminal of the isolation module 150 outputs a first level signal; when the fifth level signal is input to the input terminal of the isolation module 150, the output terminal of the isolation module 150 outputs a second level signal; and when the sixth level signal is input to the input terminal of the isolation module 150, the output terminal of the isolation module 150 outputs a third level signal. The isolation module 150 can improve the electrical isolation effect of the adjustment circuit by connecting the signal at the input terminal of the isolation module 150 to the level input terminal 111, thereby reducing circuit noise and improving the stability and reliability of the circuit. The isolation module 150 is particularly suitable for circuits requiring primary and secondary safety isolation.

[0055] In some embodiments, such as Figure 3 As shown, the isolation module 150 includes an optocoupler U1, which can realize level conversion between input and output. The following explanation uses an example where VCC voltage is 10V and the impedances of the first resistor R1, the second resistor R2, and the third resistor R3 are all 5.1KΩ. When VCON1 is low, the transmitter of optocoupler U1 is in the cutoff state, and the receiver of optocoupler U1 is in the off state. The gate voltages of the drive pins (G) of MOSFETs Q1 and Q2 are both zero, so MOSFETs Q1 and Q2 are in the cutoff state, DS is off, and the impedance of FB to ground is the impedance across R1, approximately 5.1KΩ.

[0056] When VCON1 is high, the transmitter of optocoupler U1 is in the on state, and the receiver of optocoupler U1 is also in the on state. The voltage across R4 is about 8.2V, so the gate voltage of the drive pins of MOSFETs Q1 and Q2 is about 7.5V. MOSFETs Q1 and Q2 are in the on state, DS is on, and the impedance of FB to ground is R1 / / R4 / / R5, with an impedance value of about 1.7KΩ.

[0057] When VCON1 is a square wave signal (1KHz PWM -50% cycle), the transmitter and receiver of optocoupler U1 are also in PWM mode. The gate voltage of MOSFET Q1 is approximately 7.5V, and Q1 is in the on state, as is DS. However, due to filtering by R7 and C3, the voltage across Zener diode ZD1 is lower than 5.6V, preventing the gate voltage of MOSFET Q2 from reaching the turn-on voltage, thus keeping it in the off state. At this time, the impedance of FB to ground is R1 / / R4, with an impedance value of approximately 2.55KΩ.

[0058] In some embodiments, the first voltage divider module 114 further includes a diode D2, which can prevent current backflow, and the second voltage divider module 115 further includes a diode D3, which can prevent current backflow.

[0059] like Figure 7 As shown, a second aspect of this application provides a switching power supply 200, which includes an impedance adjustment circuit 100, a controller 210, and a voltage regulation module 220.

[0060] The controller 210 is connected to the level input terminal 111. The controller 210 can output a first level signal, a second level signal and a third level signal, thereby changing the resistance of the impedance adjustment circuit 100.

[0061] The voltage regulating module 220 has a feedback pin. The first end of the first impedance module 121 is connected to the feedback pin, and the second end of the first impedance module 121 is grounded. The voltage regulating module 220 is used to adjust the output voltage of the switching power supply 200 according to the resistance of the impedance adjustment circuit 100. The voltage regulating module 220 can be applied to the primary winding or the secondary winding of the transformer.

[0062] The voltage regulation module 220 can be, exemplarily, a DC-DC converter. The impedance adjustment circuit 100 can cooperate with the voltage divider circuit to form a feedback voltage Vfb. The feedback voltage is compared with a reference voltage, and the duty cycle is adjusted according to the comparison result, thereby regulating the output voltage. By dynamically changing the resistance value of the feedback resistor, the feedback voltage can be changed, thereby adjusting the output voltage.

[0063] In the accompanying drawings of this embodiment, the same or similar reference numerals correspond to the same or similar components. In the description of this application, it should be understood that if terms such as "upper," "lower," "left," "right," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, they 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, or be constructed and operated in a specific orientation. Therefore, the terms used to describe positional relationships in the drawings are only for illustrative purposes and should not be construed as limiting this application. For those skilled in the art, the specific meaning of the above terms can be understood according to the specific circumstances.

[0064] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. An impedance adjustment circuit, characterized in that, include: The conversion module has a level input terminal and a first output terminal. The level input terminal is used to input a first level signal or a second level signal. The first level signal and the second level signal have different magnitudes or waveforms. When the first level signal is input to the level input terminal, the first output terminal outputs a first voltage. When the second level signal is input to the level input terminal, the first output terminal outputs a second voltage. An impedance adjustment module includes a first impedance module and a second impedance module. A first terminal of the first impedance module is used to connect to an external circuit, and a second terminal of the first impedance module is used to connect to an external circuit or ground. The first impedance module is kept in a conducting state. A first terminal of the second impedance module is connected to the first terminal of the first impedance module, and a second terminal of the second impedance module is connected to the second terminal of the first impedance module. The controlled terminal of the second impedance module is connected to the first output terminal. Specifically, when the first output terminal outputs the first voltage, the second impedance module is disconnected; when the first output terminal outputs the second voltage, the second impedance module is turned on.

2. The impedance adjustment circuit according to claim 1, characterized in that, The conversion module also has a second output terminal, and the level input terminal can selectively input the first level signal, the second level signal, or the third level signal, wherein the third level signal is different in magnitude or waveform from the first level signal, and the third level signal is different in magnitude or waveform from the second level signal; When the first level signal is input to the level input terminal, the second output terminal outputs a third voltage; when the second level signal is input to the level input terminal, the second output terminal outputs a fourth voltage. When the third level signal is input at the level input terminal, the first output terminal outputs the second voltage or the fifth voltage, and the second output terminal outputs the third voltage or the sixth voltage. The impedance adjustment module further includes a third impedance module, the first end of which is connected to the first end of the first impedance module, the second end of which is connected to the second end of the first impedance module, and the controlled end of the third impedance module is connected to the second output end. Specifically, when the first output terminal outputs the fifth voltage, the second impedance module is turned on; when the second output terminal outputs the third voltage or the sixth voltage, the third impedance module is turned off; when the second output terminal outputs the fourth voltage, the third impedance module is turned on.

3. The impedance adjustment circuit according to claim 2, characterized in that, The first impedance module includes a first resistor, a first end of which is used to connect to an external circuit, and a second end of which is grounded. The second impedance module includes a second resistor and a first switching transistor. The first end of the second resistor is connected to the first end of the first resistor, the second end of the second resistor is connected to the input end of the first switching transistor, the output end of the first switching transistor is grounded, and the controlled end of the first switching transistor is connected to the first output end. The third impedance module includes a third resistor and a second switching transistor. The first end of the third resistor is connected to the first end of the first resistor, the second end of the third resistor is connected to the input end of the second switching transistor, the output end of the second switching transistor is grounded, and the controlled end of the second switching transistor is connected to the second output end.

4. The impedance adjustment circuit according to claim 2, characterized in that, The conversion module includes: A first voltage divider module, wherein a first terminal of the first voltage divider module is connected to the level input terminal and the first output terminal, and a second terminal of the first voltage divider module is grounded; The second voltage divider module has a first terminal connected to the first terminal of the first voltage divider module, a second terminal connected to the second terminal of the first voltage divider module, and a third terminal connected to the second output terminal.

5. The impedance adjustment circuit according to claim 4, characterized in that, The third level signal includes a square wave signal, and the second voltage divider module includes a filter module. When the square wave signal is input to the level input terminal, the filter module divides the square wave signal to make the third voltage lower than the fourth voltage, or to make the sixth voltage lower than the fourth voltage.

6. The impedance adjustment circuit according to claim 4, characterized in that, The first voltage divider module includes a first voltage divider resistor, the first end of the first voltage divider resistor is connected to the level input terminal and the first output terminal, and the second end of the first voltage divider resistor is grounded; The second voltage divider module includes a second voltage divider resistor and a filter capacitor. The first end of the second voltage divider resistor is connected to the first end of the first voltage divider resistor. The second end of the second voltage divider resistor is connected to the second output terminal and the first end of the filter capacitor. The second end of the filter capacitor is connected to the second end of the first voltage divider resistor.

7. The impedance adjustment circuit according to claim 6, characterized in that, The second voltage divider module further includes a Zener diode, the anode of which is connected to the second terminal of the second voltage divider resistor, and the cathode of which is connected to the second output terminal. When the third level signal is input to the level input terminal, the voltage at the second terminal of the voltage divider resistor is less than the forward voltage of the Zener diode; and / or The second voltage divider module further includes a discharge diode, the positive terminal of which is connected to the first end of the second voltage divider resistor, and the negative terminal of which is connected to the second end of the second voltage divider resistor.

8. The impedance adjustment circuit according to claim 2, characterized in that, The regulating circuit also includes: The first delay module has a first terminal connected to the first output terminal and a second terminal grounded. The second delay module has its first terminal connected to the second output terminal and its second terminal grounded.

9. The impedance adjustment circuit according to any one of claims 2-8, characterized in that, The impedance adjustment circuit further includes an isolation module. The input terminal of the isolation module is used to select one of a fourth level signal, a fifth level signal, and a sixth level signal. The output terminal of the isolation module is connected to the level input terminal. When the fourth level signal is input to the input terminal of the isolation module, the output terminal of the isolation module outputs the first level signal. When the fifth level signal is input to the input terminal of the isolation module, the output terminal of the isolation module outputs the second level signal. When the sixth level signal is input to the input terminal of the isolation module, the output terminal of the isolation module outputs the third level signal.

10. A switching power supply, characterized in that, include: The impedance adjustment circuit as described in any one of claims 1-9; A controller is connected to the level input terminal, and the controller is capable of outputting the first level signal and the second level signal; and The voltage regulation module has a feedback pin, a first terminal of the first impedance module is connected to the feedback pin, and a second terminal of the first impedance module is grounded. The voltage regulation module is used to adjust the output voltage of the switching power supply according to the resistance of the impedance adjustment circuit.

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