Low-impulse current ac switch control circuit and application

Abstract

The application discloses a low-impact current AC switch control circuit and application, and the circuit comprises sequentially connected AC voltage detection modules, voltage comparison modules, self-locking circuit modules and execution modules. The AC voltage detection module is coupled to an AC power supply and is used for sampling voltage and outputting a detection signal. The voltage comparison module compares the detection signal with a reference voltage and outputs a trigger signal when the detection signal is lower than the reference voltage. The self-locking circuit module is coupled to the voltage comparison module and an external control signal end and is used for outputting a self-locking signal to turn off the AC voltage detection module when the external control signal is valid and the trigger signal is received. The execution module drives a relay to act according to the trigger signal. The application generates a trigger signal near an AC voltage zero-crossing point, ensures that a relay contact is closed at the AC voltage zero-crossing point, and greatly reduces a start-up impact current.

Description

Technical Field

[0001] This invention relates to the field of AC switch control technology, and in particular to a low-inrush-current AC switch control circuit and its application. Background Technology

[0002] Because the total power of public display video walls is relatively large, their current AC control method is generally to design an AC voltage control board containing multiple relay switches. Each relay switch is responsible for turning one column of displays on and off simultaneously, with a power-on / off delay added between each column to turn them on and off sequentially.

[0003] Traditional AC power switch control for video walls, while dividing the entire video wall into several columns for sequential activation and reducing the total power consumption at the same time, results in random AC voltage phase angles at startup. If the AC voltage phase angle is 90° or 270°, an entire column of machines will start up simultaneously, charging the power frequency capacitors inside each machine. This results in a large total inrush current and a large instantaneous total power, impacting the power supply circuit and frequently triggering overcurrent protection from the leakage current circuit breaker. Summary of the Invention

[0004] The purpose of this invention is to overcome the problems of random AC voltage phase angle and excessive inrush current when the relay is turned on in the original relay control panel circuit. It provides a low inrush current AC switch control circuit and its application, which can control the relay to close its contacts near the zero-crossing point of the AC voltage, thereby achieving zero current inrush or very low inrush current when the device is turned on, and avoiding overcurrent protection of the leakage current protector.

[0005] The technical solution adopted in this invention is:

[0006] A low-inrush-current AC switch control circuit includes an AC voltage detection module, a voltage comparison module, a self-locking circuit module, and an execution module;

[0007] The input terminal of the AC voltage detection module is coupled to the AC power supply to detect the voltage of the AC power supply, sample it, and output a detection signal.

[0008] The first input terminal of the voltage comparison module is coupled to the output terminal of the AC voltage detection module to receive the detection signal; its second input terminal is connected to a reference voltage; the voltage comparison module is used to compare the detection signal with a reference voltage, and when the detection signal is lower than the reference voltage, the output terminal of the voltage comparison module outputs a trigger signal.

[0009] The first input terminal of the self-locking circuit module is coupled to the output terminal of the voltage comparison module to receive a trigger signal. Its second input terminal is connected to a control signal, and its output terminal is coupled to a control terminal of the AC voltage detection module. The self-locking circuit module is used to output a self-locking signal to the control terminal of the AC voltage detection module to turn off the output of the detection signal when the control signal is valid and the trigger signal is received.

[0010] The input of the execution module is coupled to the output of the voltage comparator module to receive a trigger signal, and its output is coupled to the control coil of a relay. The execution module is used to respond to the trigger signal to drive the control coil of the relay to be energized, thereby closing the contacts of the relay.

[0011] The AC voltage detection module's detection signal causes the voltage comparison module to output a trigger signal when the AC power supply's voltage phase is near the zero-crossing point. Furthermore, the delay time of the relay's contact closing action matches the time of triggering the AC voltage zero-crossing point, ensuring that the relay's contacts close at or near the AC power supply's voltage zero-crossing point.

[0012] Furthermore, the AC voltage detection module includes a rectifier unit, a voltage divider unit, and a controlled switch unit;

[0013] The input terminal of the rectifier unit is coupled to an AC power supply to convert AC voltage into DC voltage;

[0014] The input terminal of the voltage divider unit is coupled to the output terminal of the rectifier unit and is used to divide the DC voltage.

[0015] The controlled switch unit is connected in series between the voltage divider units. The control terminal of the controlled switch unit is coupled to the output terminal of the self-locking circuit module and the external control signal. The controlled switch unit is turned on when the external control signal is valid and no self-locking signal is received, so as to output a detection signal from one voltage divider node of the voltage divider unit.

[0016] Furthermore, the voltage divider unit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor;

[0017] The first resistor and the second resistor are respectively coupled to the two ends of the AC power supply via their respective rectifier units, and the second resistor and the second resistor are connected together to the first end of the third resistor.

[0018] The second end of the third resistor is connected in series with the fourth, fifth, and sixth resistors, and then connected to the first conducting terminal of the controlled switch unit. The second conducting terminal of the controlled switch unit is connected to one end of the seventh resistor, and the other end of the seventh resistor is grounded. The control terminal of the controlled switch unit serves as the control terminal of the aforementioned AC voltage detection module. The voltage divider node is located between the seventh resistor and the second conducting terminal of the controlled switch unit. The AC phase angle corresponding to the reference voltage is set by adjusting the resistance ratio of the multiple series resistors.

[0019] Furthermore, the voltage comparison module includes a controllable precision voltage regulator. The reference terminal of the controllable precision voltage regulator is coupled to the detection signal as the first input terminal of the voltage comparison module. The anode of the controllable precision voltage regulator is grounded, and the cathode of the controllable precision voltage regulator is output as the output terminal of the voltage comparison module to output a trigger signal.

[0020] Furthermore, the self-locking circuit module includes a first transistor, a second transistor, a first capacitor, and an eighth resistor;

[0021] The base of the first transistor is coupled to the output of the voltage comparator module via the first capacitor and grounded via the eighth resistor;

[0022] The emitter of the first transistor is grounded, and the collector of the first transistor is coupled to the base of the second transistor; the emitter of the second transistor is coupled to the control terminal of the AC voltage detection module, and the collector of the second transistor is coupled to the base of the first transistor to form a positive feedback structure.

[0023] When the trigger signal is generated, the first capacitor is charged and the voltage drop generated across the eighth resistor drives the first transistor to conduct, thereby triggering the first transistor and the second transistor to enter a saturated conduction self-locking state, forming a self-locking signal output to the control terminal of the AC voltage detection module.

[0024] Furthermore, the self-locking circuit module also includes a first diode, the anode of which is grounded and the cathode of which is coupled to the common connection point of the first capacitor and the eighth resistor, for providing a discharge circuit for the first capacitor when the external control signal is invalid.

[0025] Furthermore, the execution module includes a switching transistor, a Zener diode, and a relay; the control terminal of the switching transistor is coupled to the output terminal (trigger signal) of the voltage comparator module via the Zener diode; the first conducting terminal of the switching transistor is grounded, and the second conducting terminal of the switching transistor is coupled to one end of the control coil of the relay; the other end of the control coil of the relay is coupled to a DC power supply.

[0026] Furthermore, the switching device in the execution module is a metal-oxide-semiconductor field-effect transistor.

[0027] Furthermore, the execution module also includes a freewheeling diode, the cathode of which is coupled to a DC power supply and the anode of which is coupled to the second conducting terminal of the switching transistor, for providing a freewheeling circuit for the induced electromotive force generated by the relay coil when the switching transistor is turned off.

[0028] Furthermore, the average delay time from the relay coil being energized to the contact closing is 5 milliseconds, the AC power supply is 50Hz or 60Hz industrial frequency, and the voltage divider network is configured to generate a trigger signal when the AC voltage phase angle is 18 degrees.

[0029] A video wall system includes at least one display unit and a low-inrush current AC switch control circuit, which controls the AC power input of the display unit (typically a row).

[0030] The present invention, employing the above technical solution, has the following beneficial effects compared with the prior art: 1) By precisely controlling the relay to close at (or near) the AC voltage zero-crossing point, the huge surge current generated during traditional random phase start-up is fundamentally avoided. This significantly reduces the instantaneous impact on the power supply circuit, effectively preventing the problem of triggering the front-end leakage protection device or air switch overcurrent protection due to excessive surge current, and improving the start-up reliability of the entire video wall system. 2) The start-up surge current of the present invention is greatly reduced, improving the reliability of the power supply of a single display screen, and also reducing the aging or damage of components caused by frequent high current surges, thereby extending the service life of the entire video wall system. 3) By adjusting the resistance value of the voltage divider resistor in the AC voltage detection circuit, the AC voltage phase angle corresponding to the trigger threshold can be flexibly set, enabling the circuit to adapt to relays of different models and with different action delay times. Through calculation and matching, it can always be ensured that the relay contacts are aligned with the voltage zero-crossing point at the actual closing moment, enhancing the versatility and engineering adaptability of the solution. 4) A self-locking circuit module has been introduced. Once the relay is successfully triggered and closed at the zero-crossing point, the circuit enters a self-locking state and stops continuous detection of AC voltage. This avoids malfunction of the relay during the conduction period, ensures the stability of the switching state, and also reliably resets when the power-off signal (PS_ON goes low) arrives, preparing for the next zero-impact power-on.

[0031] This invention achieves "soft start" of the AC power supply for video walls by matching the zero-crossing phase control with the mechanical delay of the relay, fundamentally solving the industry problem of excessive inrush current. It has significant advantages such as high reliability, good adaptability, and ease of implementation. Attached Figure Description

[0032] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments;

[0033] Figure 1This is a schematic diagram of the structure of a low-inrush-current AC switch control circuit and its application according to the present invention;

[0034] Figure 2 This is a schematic diagram of the relay's operation process time report, which is a specific example of the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings.

[0036] like Figure 1 As shown in Figure 2, the present invention discloses a low-inrush current AC switch control circuit, including an AC voltage detection module, a voltage comparison module, a self-locking circuit module, and an execution module.

[0037] The input terminal of the AC voltage detection module is coupled to the AC power supply to detect the voltage of the AC power supply, sample it, and output a detection signal.

[0038] The first input terminal of the voltage comparison module is coupled to the output terminal of the AC voltage detection module to receive the detection signal; its second input terminal is connected to a reference voltage; the voltage comparison module is used to compare the detection signal with a reference voltage, and when the detection signal is lower than the reference voltage, the output terminal of the voltage comparison module outputs a trigger signal.

[0039] The first input terminal of the self-locking circuit module is coupled to the output terminal of the voltage comparison module to receive a trigger signal. Its second input terminal is connected to a control signal, and its output terminal is coupled to a control terminal of the AC voltage detection module. The self-locking circuit module is used to output a self-locking signal to the control terminal of the AC voltage detection module to turn off the output of the detection signal when the control signal is valid and the trigger signal is received.

[0040] The input of the execution module is coupled to the output of the voltage comparator module to receive a trigger signal, and its output is coupled to the control coil of a relay. The execution module is used to respond to the trigger signal to drive the control coil of the relay to be energized, thereby closing the contacts of the relay.

[0041] The AC voltage detection module's detection signal causes the voltage comparison module to output a trigger signal when the AC power supply's voltage phase is near the zero-crossing point. Furthermore, the delay time of the relay's contact closing action matches the time of triggering the AC voltage zero-crossing point, ensuring that the relay's contacts close at or near the AC power supply's voltage zero-crossing point.

[0042] Furthermore, the AC voltage detection module includes a rectifier unit, a voltage divider unit, and a controlled switch unit;

[0043] The input terminal of the rectifier unit is coupled to an AC power supply to convert AC voltage into DC voltage;

[0044] The input terminal of the voltage divider unit is coupled to the output terminal of the rectifier unit and is used to divide the DC voltage.

[0045] The controlled switch unit is connected in series between the voltage divider units. The control terminal of the controlled switch unit is coupled to the output terminal of the self-locking circuit module and the external control signal. The controlled switch unit is turned on when the external control signal is valid and no self-locking signal is received, so as to output a detection signal from one voltage divider node of the voltage divider unit.

[0046] Furthermore, the voltage divider unit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor;

[0047] The first resistor and the second resistor are respectively coupled to the two ends of the AC power supply via their respective rectifier units, and the second resistor and the second resistor are connected together to the first end of the third resistor.

[0048] The second end of the third resistor is connected in series with the fourth, fifth, and sixth resistors, and then connected to the first conducting terminal of the controlled switch unit. The second conducting terminal of the controlled switch unit is connected to one end of the seventh resistor, and the other end of the seventh resistor is grounded. The control terminal of the controlled switch unit serves as the control terminal of the AC voltage detection module. The voltage divider node is located between the seventh resistor and the second conducting terminal of the controlled switch unit. The AC phase angle corresponding to the reference voltage is set by adjusting the resistance ratio of the multiple series resistors.

[0049] Furthermore, the voltage comparison module includes a controllable precision voltage regulator. The reference terminal of the controllable precision voltage regulator is coupled to the detection signal as the first input terminal of the voltage comparison module. The anode of the controllable precision voltage regulator is grounded, and the cathode of the controllable precision voltage regulator is output as the output terminal of the voltage comparison module to output a trigger signal.

[0050] Furthermore, the self-locking circuit module includes a first transistor, a second transistor, a first capacitor, and an eighth resistor;

[0051] The base of the first transistor is coupled to the output of the voltage comparator module via the first capacitor and grounded via the eighth resistor;

[0052] The emitter of the first transistor is grounded, and the collector of the first transistor is coupled to the base of the second transistor; the emitter of the second transistor is coupled to the control terminal of the AC voltage detection module, and the collector of the second transistor is coupled to the base of the first transistor to form a positive feedback structure.

[0053] When the trigger signal is generated, the first capacitor is charged and the voltage drop generated across the eighth resistor drives the first transistor to conduct, thereby triggering the first transistor and the second transistor to enter a saturated conduction self-locking state, forming a self-locking signal output to the control terminal of the AC voltage detection module.

[0054] Furthermore, the self-locking circuit module also includes a first diode, the anode of which is grounded and the cathode of which is coupled to the common connection point of the first capacitor and the eighth resistor, for providing a discharge circuit for the first capacitor when the external control signal is invalid.

[0055] Furthermore, the execution module includes a switching transistor, a Zener diode, and a relay; the control terminal of the switching transistor is coupled to the output terminal (trigger signal) of the voltage comparator module via the Zener diode; the first conducting terminal of the switching transistor is grounded, and the second conducting terminal of the switching transistor is coupled to one end of the control coil of the relay; the other end of the control coil of the relay is coupled to a DC power supply.

[0056] Furthermore, the switching device in the execution module is a metal-oxide-semiconductor field-effect transistor.

[0057] Furthermore, the execution module also includes a freewheeling diode, the cathode of which is coupled to a DC power supply and the anode of which is coupled to the second conducting terminal of the switching transistor, for providing a freewheeling circuit for the induced electromotive force generated by the relay coil when the switching transistor is turned off.

[0058] Furthermore, the average delay time from the relay coil being energized to the contact closing is 5 milliseconds, the AC power supply is 50Hz or 60Hz industrial frequency, and the voltage divider network is configured to generate a trigger signal when the AC voltage phase angle is 18 degrees.

[0059] A video wall system includes at least one display unit and a low-inrush current AC switch control circuit, which controls the AC power input of the display unit (typically a row).

[0060] The circuit working principle of the present invention will be described in detail below:

[0061] The AC switch control circuit of a specific embodiment of the present invention includes the following circuit modules: AC voltage detection module, voltage comparison module, self-locking circuit module, and execution module.

[0062] (1) Circuit connection relationship of AC voltage detection module: The positive terminal of diode D9910 is connected to the live wire (L) of AC power grid, and the negative terminal is connected to one end of resistor R9941; the positive terminal of diode D9911 is connected to the neutral wire (N) of AC power grid, and the negative terminal is connected to one end of resistor R9942; diode D9910 and resistor R9941 and diode D9911 and resistor R9942 constitute a rectifier bridge structure.

[0063] The other end of resistor R9942 is connected to the other end of resistor R9941 and one end of resistor R9943; the other end of resistor R9943 is connected to one end of resistor R9952, the other end of resistor R9952 is connected to one end of resistor R9953, the other end of resistor R9953 is connected to one end of resistor R9944, and the other end of resistor R9944 is connected to the drain of MOSFET Q9907, which acts as a controlled switch; the source terminal of MOSFET Q9907 is connected to one end of resistor R9947, the reference terminal of voltage regulator U9906, and the cathode of diode D9914; the other end of resistor R9947 is grounded; the gate of MOSFET Q9907 is connected to one end of C9976, one end of resistor R9964, one end of resistor R9961, and one end of resistor R9963; the other ends of capacitor C9976 and resistor R9964 are both grounded; the other end of resistor R9963 is connected to the PS_ON control signal terminal.

[0064] The AC sinusoidal voltage from the power grid is rectified into a half-sinusoidal voltage by diodes D9910 and D9911. Resistors R9941 and R9942 are current-limiting resistors to prevent overvoltage failure of diodes D9910 and D9911 due to lightning strikes. The rectified half-sinusoidal voltage is then divided by resistors R9941, R9942, R9943, R9952, R9953, R9944, the drain-source junction of MOSFET Q9907, and resistor R9947. When the PS_ON control signal is high, MOSFET Q9907, acting as a controlled switch, is saturated and turned on. The voltage across resistor R9947 serves as the AC voltage detection signal, which is output to the voltage comparator module.

[0065] (2) Circuit connection of voltage comparison module: The reference terminal of voltage regulator U9906 is connected to the negative terminal of diode D9914, one end of resistor R9947, and the other end of resistor R9947 is grounded; the positive terminal of diode D9914 is connected to one end of resistor R9971, one end of resistor R9972, and the drain of MOSFET Q9908; the other end of resistor R9972 is grounded; the other end of resistor R9971 is connected to the Vcc_12V power supply terminal; the S terminal of MOSFET Q9908 is grounded, and the MOSFET Q9908... The G terminal of 08 is connected to one end of resistor R9973, one end of capacitor C9927, and one end of resistor R9974; the other ends of resistor R9973 and capacitor C9927 are grounded; the other end of resistor R9974 is connected to the PS_ON control signal terminal; the anode of voltage regulator U9906 is grounded; the cathode of voltage regulator U9906 is connected to one end of resistor R9966, one end of capacitor C9974, and the negative terminal of Zener diode ZD9110; the other end of resistor R9966 is connected to the Vcc_12V power supply terminal.

[0066] When PS_ON is low, MOSFETs Q9907 and Q9908 are both off. The voltage across resistor R9972 is VCC_12V, which is divided across resistors R9971 and R9972. This voltage is then applied to the reference terminal of voltage regulator U9906 via diode D9914. This voltage is higher than the internal reference voltage of 1.25V at the reference terminal of voltage regulator U9906. Therefore, voltage regulator U9906 is in saturation at this time, and the voltage across its anode and cathode is 1.25V, which is lower than the voltage regulation value of Zener diode ZD9110. Zener diode ZD9110 is then off.

[0067] When PS_ON is high, MOSFETs Q9907 and Q9908 are both saturated and conducting. The voltage across resistor R9947 is the AC voltage detection signal. The voltage across resistor R9972 is pulled down to zero volts by MOSFET Q9908, so diode D9914 is cut off. When the voltage across resistor R9947 is lower than the internal reference voltage of 1.25V at the reference terminal of voltage regulator U9906, the anode and cathode voltages of voltage regulator U9906 rise rapidly. When the anode and cathode voltages of voltage regulator U9906 are greater than the voltage regulation value of Zener diode ZD9110 and the gate Miller plateau voltage of MOSFET Q803 (which acts as a switching device), MOSFET Q803 is saturated and conducting.

[0068] (3) Circuit connection relationship of the self-locking circuit module: one end of capacitor C9974 is connected to the cathode of voltage regulator U9906, one end of resistor R9966, and the cathode of voltage regulator diode ZD9110; the other end of resistor R9966 is connected to VCC_12V; the other end of capacitor C9974 is connected to one end of resistor R9970, the cathode of diode D9913, and one end of resistor R9958; the anode of diode D9913 and the other end of resistor R9970 are grounded, and the other end of resistor R9958 is connected to one end of capacitor C9975. The collector of transistor Q9906 is connected to the base of transistor Q9905; the other end of capacitor C9975 is grounded; the emitter of transistor Q9905 is grounded; the collector of transistor Q9905 is connected to the base of transistor Q9906; the emitter of transistor Q9906 is connected to one end of resistor R9961; the other end of resistor R9961 is connected to one end of resistor R9963; one end of resistor R9964 is connected to one end of capacitor C9976; and the gate of MOSFET Q9907 is connected to one end of resistor R9963; the other end of resistor R9963 is connected to the PS_ON control signal terminal.

[0069] When PS_ON is low, MOSFETs Q9907 and Q9908 are off. The voltage across resistor R9972, minus the forward voltage drop of diode D9914, is still greater than the internal reference voltage of 1.25V at the reference terminal of regulator U9906. Therefore, the anode and cathode voltages of regulator U9906 drop rapidly. The voltage across capacitor C9974 discharges rapidly through diode D9913 to the anode and cathode of regulator U9906, and the anode and cathode voltages quickly stabilize to 1.25V.

[0070] When PS_ON goes high, MOSFETs Q9907 and Q9908 are saturated and conducting, the voltage across resistor R9972 is pulled down to zero, and diode D9914 is cut off. When the voltage across resistor R9947 is lower than the internal reference voltage of 1.25V at the reference terminal of voltage regulator U9906, the voltage at the anode and cathode of voltage regulator U9906 rises rapidly. At this time, VCC_12V charges capacitor C9974 through resistor R9966, capacitor C9974, and resistor R9970. When the voltage drop across resistor R9970 is higher than the junction voltage of the BE junction of transistor Q9905, current is injected into the base of transistor Q9905, turning on transistor Q9905. Simultaneously, transistor Q9906 also begins to conduct, with current flowing into transistor Q9905. The collector current amplifies the current injected into the base by a factor of β_transistor Q9905. This current is provided by the base of transistor Q9906, which then amplifies its base current by a factor of β_transistor Q9906 and injects it into the base of transistor Q9905. This process is a positive feedback process, instantly causing transistors Q9905 and Q9906 to enter saturation conduction, grounding resistor R9961. The PS_ON voltage drop across resistors R9961 and R9964 is lower than the gate threshold voltage of MOSFET Q9907, causing MOSFET Q9907 to turn off. The AC voltage detection circuit is blocked and maintains a latched state, and the voltage across resistor R9947 remains at zero volts. When PS_ON changes from high to low, transistors Q9906 and Q9905 return to cutoff.

[0071] (4) Circuit connection relationship of the execution module: The negative terminal of the Zener diode ZD9910 is connected to the cathode of the voltage regulator U9906, one end of the capacitor C9974, and one end of the resistor R9966; the positive terminal of the Zener diode ZD9910 is connected to one end of the resistor R9956 and the gate of the MOSFET Q803; the other end of the resistor R9956 is grounded; the source of the MOSFET Q803 is grounded; the drain of the MOSFET Q803 is connected to the positive terminal of the diode D9915 and the PIN5 terminal of the relay RL1; the negative terminal of the diode D9915 is connected to VCC_12V; the PIN6 terminal of the relay RL1 is connected to VCC_12V; the PIN1 terminal of the relay RL1 is connected to the neutral line (N) of the AC mains; the PIN3 terminal of the relay RL1 is connected to the neutral line (N) of the internal power supply; the PIN2 terminal of the relay RL1 is connected to the live line (L) of the AC mains; the PIN4 terminal of the relay RL1 is connected to the live line (L) of the internal power supply.

[0072] When the R PIN voltage of voltage regulator U9906 is higher than its internal reference voltage of 1.25V, voltage regulator U9906 is in saturation operation. Its anode and cathode voltages are 1.25V, which is lower than the voltage regulation value of Zener diode ZD9110. Therefore, Zener diode ZD9110 and MOSFET Q803 are cut off, and relay RL1 is in an open circuit state.

[0073] When the voltage at pin R of voltage regulator U9906 is lower than its internal reference voltage of 1.25V, voltage regulator U9906 is turned off. VCC_12V drives MOSFET Q803 to saturate and conduct through resistor R9966, Zener diode ZD9110, and resistor R9956. The two contacts of relay RL1 close and connect, and the AC voltage from the mains supplies power to the machine.

[0074] When the MOSFET Q803 switches from saturation conduction to cutoff, the induced electromotive force of the control coil of relay RL1 is clamped by diode D9915 to prevent overvoltage failure of the emitter of MOSFET Q803.

[0075] Because there is a delay between the control coil of relay RL1 turning on and the contact closing, a relay with a stable delay time must be selected. The voltage divider resistor value of the detection circuit should be set according to its delay time characteristic so that the contact closing moment of relay RL1 coincides with or is near the zero-crossing point of the AC voltage.

[0076] like Figure 2 The figure shows the contact action time (i.e., delay time) CPK value of the relay HF30F-12-2HTF. From this test data, it can be seen that the average delay time is approximately 5ms, which is exactly one cycle of the rectified half-sine wave voltage of a 50Hz AC voltage.

[0077] The present invention, employing the above technical solution, has the following beneficial effects compared with the prior art: 1) By precisely controlling the relay to close at (or near) the AC voltage zero-crossing point, the huge surge current generated during traditional random phase start-up is fundamentally avoided. This significantly reduces the instantaneous impact on the power supply circuit, effectively preventing the problem of triggering the front-end leakage protection device or air switch overcurrent protection due to excessive surge current, and improving the start-up reliability of the entire video wall system. 2) The start-up surge current of the present invention is greatly reduced, improving the reliability of the power supply of a single display screen, and also reducing the aging or damage of components caused by frequent high current surges, thereby extending the service life of the entire video wall system. 3) By adjusting the resistance value of the voltage divider resistor in the AC voltage detection circuit, the AC voltage phase angle corresponding to the trigger threshold can be flexibly set, enabling the circuit to adapt to relays of different models and with different action delay times. Through calculation and matching, it can always be ensured that the relay contacts are aligned with the voltage zero-crossing point at the actual closing moment, enhancing the versatility and engineering adaptability of the solution. 4) A self-locking circuit module has been introduced. Once the relay is successfully triggered and closed at the zero-crossing point, the circuit enters a self-locking state and stops continuous detection of AC voltage. This avoids malfunction of the relay during the conduction period, ensures the stability of the switching state, and also reliably resets when the power-off signal (PS_ON goes low) arrives, preparing for the next zero-impact power-on.

[0078] This invention achieves "soft start" of the AC power supply for video walls by matching the zero-crossing phase control with the mechanical delay of the relay, fundamentally solving the industry problem of excessive inrush current. It has significant advantages such as high reliability, good adaptability, and ease of implementation.

[0079] Obviously, the described embodiments are only a part of the embodiments of this application, not all of them. Without conflict, the embodiments and features in the embodiments of this application can be combined with each other. The components of the embodiments of this application described and illustrated herein can generally be arranged and designed in various different configurations. Therefore, the detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

1. A low-inrush-current AC switch control circuit, characterized in that, It includes an AC voltage detection module, a voltage comparison module, a self-locking circuit module, and an execution module; The input terminal of the AC voltage detection module is coupled to the AC power supply to detect the voltage of the AC power supply, sample it, and output a detection signal. The first input terminal of the voltage comparison module is coupled to the output terminal of the AC voltage detection module to receive the detection signal; Its second input terminal is connected to a reference voltage; the voltage comparison module is used to compare the detection signal with a reference voltage, and when the detection signal is lower than the reference voltage, the output terminal of the voltage comparison module outputs a trigger signal; The first input terminal of the self-locking circuit module is coupled to the output terminal of the voltage comparison module to receive a trigger signal. Its second input terminal is connected to a control signal, and its output terminal is coupled to a control terminal of the AC voltage detection module. The self-locking circuit module is used to output a self-locking signal to the control terminal of the AC voltage detection module to turn off the output of the detection signal when the control signal is valid and the trigger signal is received. The input of the execution module is coupled to the output of the voltage comparison module to receive the trigger signal, and its output is coupled to the control coil of a relay. The execution module is used to respond to trigger signals to energize the control coil of the relay, thereby closing the relay contacts; The AC voltage detection module's detection signal causes the voltage comparison module to output a trigger signal when the AC power supply's voltage phase is near the zero-crossing point. Furthermore, the delay time of the relay's contact closing action matches the time of triggering the AC voltage zero-crossing point, ensuring that the relay's contacts close at or near the AC power supply's voltage zero-crossing point.

2. The low-inrush-current AC switch control circuit according to claim 1, characterized in that, The AC voltage detection module includes a rectifier unit, a voltage divider unit, and a controlled switch unit; The input terminal of the rectifier unit is coupled to an AC power supply to convert AC voltage into DC voltage; The input terminal of the voltage divider unit is coupled to the output terminal of the rectifier unit and is used to divide the DC voltage. The controlled switch unit is connected in series between the voltage divider units. The control terminal of the controlled switch unit is coupled to the output terminal of the self-locking circuit module and the external control signal. The controlled switch unit is turned on when the external control signal is valid and no self-locking signal is received, so as to output a detection signal from one voltage divider node of the voltage divider unit.

3. The low-inrush current AC switch control circuit according to claim 2, characterized in that, The voltage divider unit includes a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, and a seventh resistor; The first resistor and the second resistor are respectively coupled to the two ends of the AC power supply via their respective rectifier units, and the second resistor and the second resistor are connected together to the first end of the third resistor. The second end of the third resistor is connected in series with the fourth, fifth, and sixth resistors, and then connected to the first conducting terminal of the controlled switch unit. The second conducting terminal of the controlled switch unit is connected to one end of the seventh resistor, and the other end of the seventh resistor is grounded. The control terminal of the controlled switch unit serves as the control terminal of the AC voltage detection module. The voltage divider node is located between the seventh resistor and the second conducting terminal of the controlled switch unit. The AC phase angle corresponding to the reference voltage is set by adjusting the resistance ratio of the multiple series resistors.

4. The low-inrush current AC switch control circuit according to claim 1, characterized in that, The voltage comparison module includes a controllable precision voltage regulator. The reference terminal of the controllable precision voltage regulator is used as the first input terminal of the voltage comparison module and coupled to the detection signal. The anode of the controllable precision voltage regulator is grounded, and the cathode of the controllable precision voltage regulator is used as the output terminal of the voltage comparison module to output a trigger signal.

5. The low-inrush current AC switch control circuit according to claim 1, characterized in that, The self-locking circuit module includes a first transistor, a second transistor, a first capacitor, and an eighth resistor; The base of the first transistor is coupled to the output of the voltage comparator module via the first capacitor and grounded via the eighth resistor; The emitter of the first transistor is grounded, and the collector of the first transistor is coupled to the base of the second transistor; the emitter of the second transistor is coupled to the control terminal of the AC voltage detection module, and the collector of the second transistor is coupled to the base of the first transistor to form a positive feedback structure. When the trigger signal is generated, the first capacitor is charged and the voltage drop generated across the eighth resistor drives the first transistor to conduct, thereby triggering the first transistor and the second transistor to enter a saturated conduction self-locking state, forming a self-locking signal output to the control terminal of the AC voltage detection module.

6. The low-inrush current AC switch control circuit according to claim 1, characterized in that, The self-locking circuit module also includes a first diode, the anode of which is grounded and the cathode of which is coupled to the common connection point of the first capacitor and the eighth resistor, for providing a discharge circuit for the first capacitor when the external control signal is invalid.

7. The low-inrush current AC switch control circuit according to claim 1, characterized in that, The execution module includes a switching transistor, a Zener diode, and a relay; the control terminal of the switching transistor is coupled to the output terminal of the voltage comparator module via the Zener diode; the first conducting terminal of the switching transistor is grounded, and the second conducting terminal of the switching transistor is coupled to one end of the control coil of the relay; the other end of the control coil of the relay is coupled to a DC power supply.

8. The low-inrush current AC switch control circuit according to claim 7, characterized in that, The execution module also includes a freewheeling diode, the cathode of which is coupled to a DC power supply and the anode of which is coupled to the second conducting terminal of the switching transistor, for providing a freewheeling circuit for the induced electromotive force generated by the relay coil when the switching transistor is turned off.

9. A video wall system, characterized in that, It includes at least one display unit and a low-inrush current AC switch control circuit according to any one of claims 1 to 8, wherein the low-inrush current AC switch control circuit is used to control the AC power input of the display unit.

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