A primary side feedback (FB) pin short circuit protection circuit and method

Abstract

The application discloses a primary side feedback FB pin short circuit protection circuit and method, and the circuit comprises a sampling and latching module, a second comparator, an FB short circuit detection module, a logic judgment module and a main control logic module. A second comparator is added in an AC-DC chip. The negative voltage of an FB pin is compared with the reference value of the second comparator at the opening moment of the internal driving signal, so as to latch through the detection of the negative voltage state of the FB pin, control the main logic circuit to trigger protection, and quickly close the driving, so as to realize FB short circuit protection, ensure that there is no excessively high switching frequency, no excessively high output voltage and VDD voltage problem under the FB pin short circuit to the ground, reduce the risk of device damage, and automatic recovery to normal work can be realized after the fault is removed.

Description

Technical Field

[0001] This application relates to the field of AC-DC chip circuit technology, and more specifically, to a primary-side feedback FB pin short-circuit protection circuit and method. Background Technology

[0002] Currently, in traditional primary-side feedback schemes, the FB pin samples the winding voltage through upper and lower voltage divider resistors. The FB pin serves as the power system feedback pin, such as... Figure 1 The diagram shows a typical application circuit of a primary-side feedback AC / DC power supply chip in a charger. ACL and ACN are connected to AC power, which is rectified and filtered to supply power to the chip's VDD pin. The chip includes VDD, FB, CS, GND, and D pins. The voltage of the primary-side sampling winding of transformer T1 is connected to ground through resistors R3 and R4. The voltage of the sampling winding is divided by resistor R3 and sent to the FB pin for comparison and feedback control, thereby achieving stable output. During production and product use, occasional short circuits may occur between the FB pin and ground or between the sampling voltage divider resistors. The power supply needs to enter a protection state and must not damage other devices or circuits. After the fault is cleared, it can automatically return to normal operation.

[0003] In the existing solution, when the FB pin is short-circuited to ground, the voltage of the FB pin sampled internally by the chip is too low, causing the operating frequency to rise rapidly and the output power to increase. This eventually leads to an increase in the output voltage and VDD voltage, triggering VDD overvoltage protection. The chip enters a protection lockout state, and the VDD capacitor voltage naturally discharges and decreases until it reaches the VDD undervoltage point, at which point VDD restarts. In the existing protection method, there is a rapid surge in the output voltage and VDD voltage, causing the chip to enter a protection lockout state. Furthermore, after protection, the chip will repeatedly attempt to restart, and each restart carries the risk of device damage due to overvoltage.

[0004] Therefore, how to ensure that there is no excessively high switching frequency, output voltage, or VDD voltage when the FB pin is short-circuited to ground, thereby reducing the risk of device damage and enabling automatic recovery to normal operation after the fault is cleared, is a technical problem that needs to be solved. Summary of the Invention

[0005] This invention provides a primary-side feedback FB pin short-circuit protection circuit to solve the technical problem in the prior art where, when the FB pin is short-circuited to ground, the output voltage and VDD voltage rapidly surge, causing the chip to enter a protection lockout state, and repeatedly attempting to restart after protection, with each restart posing a risk of device overvoltage damage. The circuit includes:

[0006] The sampling latch module is used to acquire and store the FB pin signal of the AC-DC chip, and input the FB pin signal exceeding the first preset value into the first comparator, and input the FB pin signal below the second preset value into the second comparator;

[0007] The second comparator is used to compare the input FB pin signal with the second reference value of the second comparator to obtain a second comparison result, and send the second comparator output signal to the FB short circuit detection module according to the comparison result;

[0008] The FB short-circuit detection module is used to detect the FB short-circuit detection signal and the output signal of the second comparator, and send the FB short-circuit detection output signal to the logic judgment module based on the state of the FB short-circuit detection signal and the output signal of the second comparator. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued.

[0009] The logic judgment module is used to send a drive control signal to the main control logic module based on the FB short-circuit detection output signal;

[0010] The main control logic module is used to turn off or maintain the internal drive signal of the AC-DC chip according to the drive control signal.

[0011] In some embodiments of this application, the second comparator is specifically used for:

[0012] When the negative voltage of the FB pin signal is less than the second preset value and greater than the second reference value for at least one cycle, the second comparator output signal is high.

[0013] When the negative voltage of the FB pin signal is less than or equal to the second reference value for at least one cycle, the second comparator output signal is low.

[0014] In some embodiments of this application, the FB short-circuit detection module is specifically used for:

[0015] When the FB short-circuit detection signal is high and the second comparator output signal is high, the FB short-circuit detection output signal is high.

[0016] When the FB short-circuit detection signal is high and the second comparator output signal is low, the FB short-circuit detection output signal is low.

[0017] In some embodiments of this application, the logical judgment module specifically comprises:

[0018] When the FB short-circuit detection output signal is high, a drive shutdown signal is sent to the main control logic module, and the main control logic module is controlled to shut down the internal drive signal of the AC-DC chip after receiving the drive shutdown signal.

[0019] When the FB short-circuit detection output signal is low, a drive hold signal is sent to the main control logic module, and the main control logic module is controlled to hold the internal drive signal of the AC-DC chip after receiving the drive hold signal.

[0020] In some embodiments of this application, the system further includes the first comparator, a multi-mode control module, and a zero-crossing detection module.

[0021] The zero-crossing detection module is used to detect the zero-crossing state of the FB pin signal of the AC-DC chip. When the FB pin signal crosses zero, a valley signal is obtained and the valley signal is sent to the multi-mode control module.

[0022] The first comparator is used to compare the input FB pin signal with the first reference value of the first comparator to obtain a first comparison result, and send the first comparator output signal to the multi-mode control module according to the comparison result;

[0023] A multi-mode control module is used to generate a multi-mode control signal based on the valley signal and the output signal of the first comparator, send the multi-mode control signal to the main control logic module, select a multi-mode control type for the main control logic module, and control the main control logic module to adjust the driving frequency and duty cycle of the internal drive signal of the AC-DC chip according to the multi-mode control type and the multi-mode control signal. The multi-mode control type includes a PFM and PWM hybrid control mode or a constant current / constant voltage mode.

[0024] In some embodiments of this application, the circuit further includes a VDD over / under voltage protection module, which is directly connected to the main control logic module.

[0025] The VDD over / under voltage protection module is used to detect the VDD voltage value of the AC-DC chip. When the VDD voltage value exceeds a first preset voltage value, it sends a shutdown signal to the main control logic module, controlling the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal. When the VDD voltage value is lower than a second preset voltage value, it sends a power supply shutdown signal to the main control logic module, controlling the main control logic module to stop supplying power to the AC-DC chip after receiving the power supply shutdown signal.

[0026] In some embodiments of this application, the circuit further includes a short-circuit protection detection module, which is connected to the main control logic module through the logic judgment module.

[0027] The short-circuit protection detection module is used to detect whether the CS pin of the AC-DC chip is short-circuited. When the CS pin is short-circuited, the logic judgment module sends a shutdown signal to the main control logic module, and controls the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal.

[0028] In some embodiments of this application, the circuit further includes an over-temperature protection detection module, and the short-circuit protection detection module is connected to the main control logic module through the logic judgment module.

[0029] The over-temperature protection detection module is used to send a shutdown signal to the main control logic module through the logic judgment module when the chip temperature of the AC-DC chip reaches a preset temperature value, and control the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal.

[0030] Accordingly, the present invention also proposes a method for short-circuit protection of the primary-side feedback FB pin, the method comprising:

[0031] The sampling latch module collects and stores the FB pin signal of the AC-DC chip, and inputs the FB pin signal exceeding the first preset value into the first comparator, and inputs the FB pin signal below the second preset value into the second comparator.

[0032] The FB pin signal input to the second comparator is compared with the second reference value of the second comparator to obtain a second comparison result, and the second comparator output signal is sent to the FB short circuit detection module according to the comparison result;

[0033] The FB short-circuit detection module sends an FB short-circuit detection output signal to the logic judgment module based on the second comparator output signal and the FB short-circuit detection signal. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued.

[0034] The logic judgment module sends a drive control signal to the main control logic module based on the FB short-circuit detection output signal.

[0035] The main control logic module receives the over / under voltage output signal sent by the VDD over / under voltage protection module and the drive control signal, and controls the internal drive signal of the AC-DC chip based on the over / under voltage output signal and the drive control signal.

[0036] In some embodiments of this application, the internal drive signal of the AC-DC chip is controlled based on the over / under voltage output signal and the drive control signal, specifically as follows:

[0037] When the VDD voltage exceeds the first preset voltage value, VDD is in an overvoltage state and sends a shutdown signal to the main control logic module, controlling the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal;

[0038] When the VDD voltage value is lower than the second preset voltage value, VDD is in an undervoltage state and sends a power supply shutdown signal to the main control logic module, controlling the main control logic module to stop supplying power to the AC-DC chip after receiving the power supply shutdown signal;

[0039] When the FB short-circuit detection signal is high and the negative voltage of the FB pin signal is less than the second preset value and greater than the second reference value for at least one cycle, the FB short-circuit detection output signal is high, the logic judgment module sends a drive shutdown signal to the main control logic module, and controls the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the drive shutdown signal.

[0040] When the FB short-circuit detection signal is low and the negative voltage of the FB pin signal is less than or equal to the second reference value for at least one cycle, the FB short-circuit detection output signal is low, the logic judgment module sends a drive hold signal to the main control logic module, and controls the main control logic module to hold the internal drive signal of the AC-DC chip after receiving the drive hold signal.

[0041] By applying the above technical solutions, a primary-side feedback FB pin short-circuit protection circuit is proposed. The circuit includes: a sampling latch module for acquiring and storing the FB pin signal of the AC-DC chip, inputting FB pin signals exceeding a first preset value to a first comparator, and inputting FB pin signals below a second preset value to a second comparator; the second comparator for comparing the input FB pin signal with a second reference value of the second comparator to obtain a second comparison result, and sending a second comparator output signal to an FB short-circuit detection module based on the comparison result; and the FB short-circuit detection module for detecting the FB short-circuit detection signal and the second comparator output signal, and based on the states of the FB short-circuit detection signal and the second comparator output signal... The logic judgment module sends an FB short-circuit detection output signal, which is generated synchronously when the internal drive signal of the AC-DC chip is emitted. The logic judgment module is used to send a drive control signal to the main control logic module according to the FB short-circuit detection output signal. The main control logic module is used to turn off or maintain the internal drive signal of the AC-DC chip according to the drive control signal, thereby latching by detecting the negative voltage state of the FB pin, controlling the main logic circuit to trigger protection, and quickly shutting down the drive, thereby realizing FB short-circuit protection. This ensures that there is no excessively high switching frequency, no excessively high output voltage or VDD voltage when the FB pin is short-circuited to ground, reducing the risk of device damage, and can automatically restore normal operation after the fault is cleared. Attached Figure Description

[0042] 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.

[0043] Figure 1 This diagram illustrates the application circuit of a primary-side feedback AC / DC power supply chip in a charger in the prior art.

[0044] Figure 2 This diagram illustrates a structural schematic of a primary-side feedback FB pin short-circuit protection circuit proposed in an embodiment of the present invention.

[0045] Figure 3 A flowchart illustrating a primary-side feedback FB pin short-circuit protection method proposed in an embodiment of the present invention is shown.

[0046] Figure 4 The waveform diagram of the application circuit of the primary-side feedback AC / DC power supply chip in the charger in the prior art is shown;

[0047] Figure 5The diagram shows a waveform of a primary-side feedback FB pin short-circuit protection circuit proposed in an embodiment of the present invention. Detailed Implementation

[0048] 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 some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0049] This application provides a short-circuit protection circuit for the primary-side feedback FB pin, such as... Figure 2 As shown, the circuit includes:

[0050] The sampling latch module is used to acquire and store the FB pin signal of the AC-DC chip, and input the FB pin signal exceeding the first preset value into the first comparator, and input the FB pin signal below the second preset value into the second comparator;

[0051] The second comparator is used to compare the input FB pin signal with the second reference value of the second comparator to obtain a second comparison result, and send the second comparator output signal to the FB short circuit detection module according to the comparison result;

[0052] The FB short-circuit detection module is used to detect the FB short-circuit detection signal and the output signal of the second comparator, and send the FB short-circuit detection output signal to the logic judgment module based on the state of the FB short-circuit detection signal and the output signal of the second comparator. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued.

[0053] The logic judgment module is used to send a drive control signal to the main control logic module based on the FB short-circuit detection output signal;

[0054] The main control logic module is used to turn off or maintain the internal drive signal of the AC-DC chip according to the drive control signal.

[0055] In this embodiment, a second comparator is set inside the AC-DC chip. The FB pin signal of the AC-DC chip is collected by the sampling latch module. The FB pin signal that is lower than the second preset value is input to the second comparator. The second comparator sends a second comparator output signal to the FB short-circuit detection module according to the comparison result between the input FB pin signal and the second reference value of the second comparator. The FB short-circuit detection module sends an FB short-circuit detection output signal to the logic judgment module according to the state of the FB short-circuit detection signal and the second comparator output signal. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued. The logic judgment module sends a drive control signal to the main control logic module according to the FB short-circuit detection output signal, and then controls the internal drive signal of the AC-DC chip through the main control logic module.

[0056] In order to accurately identify the negative voltage of the FB pin signal and control the second comparator to output the corresponding output signal, in some embodiments of this application, the second comparator is specifically used for:

[0057] When the negative voltage of the FB pin signal is less than the second preset value and greater than the second reference value for at least one cycle, the second comparator output signal is high.

[0058] When the negative voltage of the FB pin signal is less than or equal to the second reference value for at least one cycle, the second comparator output signal is low.

[0059] To accurately detect whether the negative voltage of the FB pin is within a safe range, in some embodiments of this application, the FB short-circuit detection module is specifically used for:

[0060] When the FB short-circuit detection signal is high and the second comparator output signal is high, the FB short-circuit detection output signal is high.

[0061] When the FB short-circuit detection signal is high and the second comparator output signal is low, the FB short-circuit detection output signal is low.

[0062] In order to send control signals to the main control logic module based on the actual situation of the FB pin signal, in some embodiments of this application, the logic judgment module specifically includes:

[0063] When the FB short-circuit detection output signal is high, a drive shutdown signal is sent to the main control logic module, and the main control logic module is controlled to shut down the internal drive signal of the AC-DC chip after receiving the drive shutdown signal.

[0064] When the FB short-circuit detection output signal is low, a drive hold signal is sent to the main control logic module, and the main control logic module is controlled to hold the internal drive signal of the AC-DC chip after receiving the drive hold signal.

[0065] In this embodiment, when the FB short-circuit detection output signal is high, it indicates that the FB pin is short-circuited to ground, and the internal drive signal of the AC-DC chip needs to be turned off. At this time, a drive shutdown signal is sent to the main control logic module. After receiving the drive shutdown signal, the main control logic module turns off the internal drive signal of the AC-DC chip. When the FB short-circuit detection output signal is low, it indicates that the FB pin signal is normal, and a drive hold signal is sent to the main control logic module. After receiving the drive hold signal, the main control logic module holds the internal drive signal of the AC-DC chip.

[0066] To adjust the driving frequency and duty cycle of the internal drive signal of the AC-DC chip, some embodiments of this application further include the first comparator, a multi-mode control module, and a zero-crossing detection module.

[0067] The zero-crossing detection module is used to detect the zero-crossing state of the FB pin signal of the AC-DC chip. When the FB pin signal crosses zero, a valley signal is obtained and the valley signal is sent to the multi-mode control module.

[0068] The first comparator is used to compare the input FB pin signal with the first reference value of the first comparator to obtain a first comparison result, and send the first comparator output signal to the multi-mode control module according to the comparison result;

[0069] A multi-mode control module is used to generate a multi-mode control signal based on the valley signal and the output signal of the first comparator, send the multi-mode control signal to the main control logic module, select a multi-mode control type for the main control logic module, and control the main control logic module to adjust the driving frequency and duty cycle of the internal drive signal of the AC-DC chip according to the multi-mode control type and the multi-mode control signal. The multi-mode control type includes a PFM and PWM hybrid control mode or a constant current / constant voltage mode.

[0070] In this embodiment, the multi-mode control module logic judges the valley signal of the FB pin and the output signal of the first comparator, and sends the output signal to the main control logic module. Multi-mode refers to PWM+PFM (PFM and PWM mixed control) and CC / CV (constant current / constant voltage) modes. The output signal of the multi-mode control module is used to adjust the driving frequency and duty cycle of the internal drive signal.

[0071] To monitor the over / under voltage status of the VDD terminal in real time, in some embodiments of this application, the circuit further includes a VDD over / under voltage protection module, which is directly connected to the main control logic module.

[0072] The VDD over / under voltage protection module is used to detect the VDD voltage value of the AC-DC chip. When the VDD voltage value exceeds a first preset voltage value, it sends a shutdown signal to the main control logic module, controlling the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal. When the VDD voltage value is lower than a second preset voltage value, it sends a power supply shutdown signal to the main control logic module, controlling the main control logic module to stop supplying power to the AC-DC chip after receiving the power supply shutdown signal.

[0073] In this embodiment, when VDD is overvoltage, the main control logic module shuts down the internal drive signal of the chip, causing the chip to enter a protection latch state. When VDD is undervoltage, the main control logic module shuts down the power supply to the chip.

[0074] Preferably, the output signals of the over / under voltage protection module and the output signals of the logic judgment module are protection logic. As long as one of the protection is triggered, that is, either output signal is high, the internal drive signal can be shut down.

[0075] To achieve short-circuit protection of the circuit, in some embodiments of this application, the circuit further includes a short-circuit protection detection module, which is connected to the main control logic module through the logic judgment module.

[0076] The short-circuit protection detection module is used to detect whether the CS pin of the AC-DC chip is short-circuited. When the CS pin is short-circuited, the logic judgment module sends a shutdown signal to the main control logic module, and controls the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal.

[0077] To achieve over-temperature protection, in some embodiments of this application, the circuit further includes an over-temperature protection detection module, which is connected to the main control logic module through the logic judgment module.

[0078] The over-temperature protection detection module is used to send a shutdown signal to the main control logic module through the logic judgment module when the chip temperature of the AC-DC chip reaches a preset temperature value, and control the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal.

[0079] Preferably, the logic judgment module judges the output signals of the FB short-circuit protection detection module, the CS short-circuit protection detection module, and the over-temperature protection detection module, and controls the generation and shutdown of the drive signal through the main control logic module. If any one of the three signals is high, the internal drive signal is shut down to ensure circuit safety.

[0080] Preferably, the circuit of this solution also includes a VCC overvoltage protection module and an OLP overload module to further improve the safety of the chip. Specifically, the VCC overvoltage protection module causes the chip to immediately stop switching when the VCC voltage exceeds its typical value. This causes VCC to drop, and when the VCC voltage falls below the turn-off voltage VCC_OFF, the system will restart. The OLP overload module detects whether the output load exceeds the power limit and limits the current cycle by CS, causing the output and FB voltages to drop, thereby achieving protection.

[0081] By applying the above technical solutions, a primary-side feedback FB pin short-circuit protection circuit is proposed. The circuit includes: a sampling latch module for acquiring and storing the FB pin signal of the AC-DC chip, inputting FB pin signals exceeding a first preset value to a first comparator, and inputting FB pin signals below a second preset value to a second comparator; the second comparator for comparing the input FB pin signal with a second reference value of the second comparator to obtain a second comparison result, and sending a second comparator output signal to an FB short-circuit detection module based on the comparison result; and the FB short-circuit detection module for detecting the FB short-circuit detection signal and the second comparator output signal, and based on the states of the FB short-circuit detection signal and the second comparator output signal... The logic judgment module sends an FB short-circuit detection output signal, which is generated synchronously when the internal drive signal of the AC-DC chip is emitted. The logic judgment module is used to send a drive control signal to the main control logic module according to the FB short-circuit detection output signal. The main control logic module is used to turn off or maintain the internal drive signal of the AC-DC chip according to the drive control signal, thereby latching by detecting the negative voltage state of the FB pin, controlling the main logic circuit to trigger protection, and quickly shutting down the drive, thereby realizing FB short-circuit protection. This ensures that there is no excessively high switching frequency, no excessively high output voltage or VDD voltage when the FB pin is short-circuited to ground, reducing the risk of device damage, and can automatically restore normal operation after the fault is cleared.

[0082] This application also proposes a method for short-circuit protection of the primary-side feedback FB pin, such as... Figure 3 As shown, the method includes:

[0083] Step S101: The sampling latch module collects and stores the FB pin signal of the AC-DC chip, and inputs the FB pin signal exceeding the first preset value into the first comparator, and inputs the FB pin signal below the second preset value into the second comparator.

[0084] Step S102: The FB pin signal input to the second comparator is compared with the second reference value of the second comparator to obtain a second comparison result, and the second comparator output signal is sent to the FB short circuit detection module according to the comparison result;

[0085] Step S103: The FB short-circuit detection module sends an FB short-circuit detection output signal to the logic judgment module based on the second comparator output signal and the FB short-circuit detection signal. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued.

[0086] Step S104: The logic judgment module sends a drive control signal to the main control logic module based on the FB short-circuit detection output signal;

[0087] In step S105, the main control logic module receives the over / under voltage output signal sent by the VDD over / under voltage protection module and the drive control signal, and controls the internal drive signal of the AC-DC chip based on the over / under voltage output signal and the drive control signal.

[0088] In this embodiment, Figure 1 An FB negative voltage detection circuit is added to the existing circuit. The negative voltage state of the FB pin is detected and latched to control the main logic circuit to trigger protection and quickly shut down the drive, thereby realizing FB short circuit protection.

[0089] Specifically: The voltage is sampled through the FB pin, and a short-circuit detection signal is synchronously generated by the internal drive signal. A second comparator (negative voltage comparator) is added inside the AC-DC chip. When the internal drive signal is turned on, the negative voltage of the FB pin is compared with the reference value of the second comparator. The reference value of the negative terminal of the negative voltage comparator is -0.3V, and the reference value range is [-0.2, -0.5]. The comparison is made to see if the negative voltage of the FB pin meets the limit requirement (greater than -0.3V and less than 0V). If the FB short-circuit detection module detects that the negative voltage does not meet the limit requirement within one or more cycles (within 10 cycles), the short-circuit detection module will detect the short voltage. When the FB short-circuit detection signal is present, the output signal of the FB short-circuit detection module is judged by the logic judgment module and then triggered to the main control logic module, which shuts down the internal drive signal. The chip enters the protection latch state until the system experiences VDD undervoltage and then re-issues the internal drive signal, causing the system to restart. When the system restarts, the internal drive signal is issued and the FB short-circuit detection signal is generated simultaneously. The FB short-circuit detection module starts to detect the negative voltage limit of the FB pin. If the negative voltage fails to meet the limit requirement for one cycle (or multiple cycles), the above protection process is repeated until the negative voltage limit of the FB pin is detected normally, the fault is cleared, and the chip works normally.

[0090] In order to control the internal drive signals of the AC-DC chip, in some embodiments of this application, a shutdown signal is sent to the main control logic module to control the main control logic module to shut down the internal drive signals of the AC-DC chip after receiving the shutdown signal;

[0091] When the VDD voltage value is lower than the second preset voltage value, VDD is in an undervoltage state and sends a power supply shutdown signal to the main control logic module, controlling the main control logic module to stop supplying power to the AC-DC chip after receiving the power supply shutdown signal;

[0092] When the FB short-circuit detection signal is high and the negative voltage of the FB pin signal is less than the second preset value and greater than the second reference value for at least one cycle, the FB short-circuit detection output signal is high, the logic judgment module sends a drive shutdown signal to the main control logic module, and controls the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the drive shutdown signal.

[0093] When the FB short-circuit detection signal is low and the negative voltage of the FB pin signal is less than or equal to the second reference value for at least one cycle, the FB short-circuit detection output signal is low, the logic judgment module sends a drive hold signal to the main control logic module, and controls the main control logic module to hold the internal drive signal of the AC-DC chip after receiving the drive hold signal.

[0094] To further illustrate the practical effects of this application, the following is combined with... Figure 1 The waveform diagrams of the existing circuit and the circuit of this scheme are explained.

[0095] like Figure 4 The waveform diagram for the existing circuit is shown below. The horizontal axis represents time, and the vertical axis represents voltage. Gate is the internal drive signal of the chip, VDS is the drain-source voltage signal of the MOSFET, FB is the chip feedback pin signal, VDD is the chip supply voltage signal, and VOUT is the chip output voltage signal. Initially, a positive pulse drive signal is applied to the gate terminal, and a positive DC operating voltage is applied to the VDD terminal. The chip starts to work, and there is a positive output voltage at the Vout terminal. When the output voltage of the FB pin is detected to be 0, the internal drive signal of the chip continues to emit pulses, and the pulse signal frequency increases. VDD and the output voltage experience a rapid surge until the VDD voltage rises to the chip's overvoltage protection point, the overvoltage protection is activated, and the chip enters the protection latch state. The VDD voltage drops naturally as the capacitor discharges, and when it drops to the VDD undervoltage point, the system restarts. The rapid surge of VDD and the output voltage poses a risk of overvoltage damage to the device.

[0096] like Figure 5 The waveform diagram of the improved circuit is shown below. The horizontal axis represents time and the vertical axis represents voltage. Gate is the internal drive signal of the chip, VDS is the drain-source voltage signal of the MOS transistor, FB is the chip feedback pin signal, FB short-circuit detection signal is the signal to detect the short circuit status of the FB pin to ground, VDD is the chip power supply voltage signal, and VOUT is the chip output voltage signal.

[0097] Initially, a positive pulse drive signal is applied to the gate terminal. The FB short-circuit detection signal is synchronized with the internal drive signal. A positive DC operating voltage is applied to the VDD terminal, and the chip starts working, with a positive output voltage at the Vout terminal. At time t1, the output voltage of the FB pin is detected to be 0. At time t2, a positive pulse drive signal is continued to be issued, and a short-circuit detection signal for the FB pin is generated synchronously. At this time, the FB short-circuit detection module detects that the negative voltage of the FB pin does not meet the limit requirement, confirming that the FB pin is short-circuited. The internal drive signal is shut down through the main control logic module, and the FB short-circuit detection signal is also shut down synchronously. The chip enters the latch protection state. t3-t At time t4, capacitor C3 discharges, and the voltage of VDD naturally decreases as capacitor C3 discharges until it drops to the chip's undervoltage point. During the period from t4 to t5, the system restarts, and the VDD voltage begins to rise to the chip's startup point. At time t5, the internal drive signal and the FB short-circuit detection signal continue to send pulse signals to detect the current short-circuit state. At this time, it is still short-circuited, and VDD and VOUT continue to decrease until the VDD voltage drops to the chip's undervoltage point, after which the system restarts again. When the short circuit on the FB pin disappears, the chip works normally. Generally, the voltage at the VDD startup point is relatively small, so there will be no phenomenon of excessively high output voltage or VDD voltage.

[0098] In summary, this invention adds an FB negative voltage detection circuit to the existing technology, and latches the negative voltage state of the FB pin to control the main logic circuit to trigger protection and quickly shut down the drive, thereby realizing FB short circuit protection.

[0099] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A primary-side feedback FB pin short-circuit protection circuit, characterized in that, The circuit includes: The sampling latch module is used to acquire and store the FB pin signal of the AC-DC chip, and will store signals exceeding... The FB pin signal with the first preset value is input to the first comparator, and the FB pin signal with the second preset value is input to the second comparator. The second comparator is used to compare the input FB pin signal with the second reference value of the second comparator to obtain a second comparison result, and send the second comparator output signal to the FB short circuit detection module according to the comparison result; The FB short-circuit detection module is used to detect the FB short-circuit detection signal and the output signal of the second comparator, and send the FB short-circuit detection output signal to the logic judgment module based on the state of the FB short-circuit detection signal and the output signal of the second comparator. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued. The logic judgment module is used to send a drive control signal to the main control logic module based on the FB short-circuit detection output signal; The main control logic module is used to turn off or maintain the internal drive signal of the AC-DC chip according to the drive control signal; It also includes the first comparator, a multi-mode control module, and a zero-crossing detection module. The zero-crossing detection module is used to detect the zero-crossing state of the FB pin signal of the AC-DC chip. When the FB pin signal crosses zero, a valley signal is obtained, and the valley signal is sent to the multi-mode control module. The first comparator is used to compare the input FB pin signal with the first reference value of the first comparator to obtain a first comparison result, and send a first comparator output signal to the multi-mode control module according to the comparison result. The multi-mode control module is used to generate a multi-mode control signal according to the valley signal and the first comparator output signal, send the multi-mode control signal to the main control logic module, select a multi-mode control type for the main control logic module, and control the main control logic module to adjust the driving frequency and duty cycle of the internal drive signal of the AC-DC chip according to the multi-mode control type and the multi-mode control signal. The multi-mode control type includes a PFM and PWM hybrid control mode or a constant current / constant voltage mode. The circuit also includes a VDD over / under voltage protection module, which is directly connected to the main control logic module. The VDD over / under voltage protection module is used to detect the VDD voltage value of the AC-DC chip. When the VDD voltage value exceeds a first preset voltage value, it sends a shutdown signal to the main control logic module, controlling the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal. When the VDD voltage value is lower than a second preset voltage value, it sends a power supply shutdown signal to the main control logic module, controlling the main control logic module to stop supplying power to the AC-DC chip after receiving the power supply shutdown signal. The circuit also includes a short-circuit protection detection module, which is connected to the main control logic module through the logic judgment module. The short-circuit protection detection module is used to detect whether the CS pin of the AC-DC chip is short-circuited. When the CS pin is short-circuited, the logic judgment module sends a shutdown signal to the main control logic module, which then controls the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal.

2. The circuit as described in claim 1, characterized in that, The second comparator is specifically used for: When the negative voltage of the FB pin signal is less than the second preset value and greater than the second reference value for at least one cycle, the second comparator output signal is high. When the negative voltage of the FB pin signal is less than or equal to the second reference value for at least one cycle, the second comparator output signal is low.

3. The circuit as described in claim 1, characterized in that, The FB short-circuit detection module is specifically used for: When the FB short-circuit detection signal is high and the second comparator output signal is high, the FB short-circuit detection output signal is high. When the FB short-circuit detection signal is high and the second comparator output signal is low, the FB short-circuit detection output signal is low.

4. The circuit as described in claim 1, characterized in that, The logical judgment module is specifically as follows: When the FB short-circuit detection output signal is high, a drive shutdown signal is sent to the main control logic module, and the main control logic module is controlled to shut down the internal drive signal of the AC-DC chip after receiving the drive shutdown signal. When the FB short-circuit detection output signal is low, a drive hold signal is sent to the main control logic module, and the main control logic module is controlled to hold the internal drive signal of the AC-DC chip after receiving the drive hold signal.

5. The circuit as described in claim 1, characterized in that, The circuit also includes an over-temperature protection detection module, which is connected to the main control logic module via the logic judgment module. The over-temperature protection detection module is used to send a shutdown signal to the main control logic module through the logic judgment module when the chip temperature of the AC-DC chip reaches a preset temperature value, and control the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal.

6. A method for short-circuit protection of the primary-side feedback FB pin, characterized in that, The method is applied to the primary-side feedback FB pin short-circuit protection circuit as described in any one of claims 1-5, and the method includes: The sampling latch module collects and stores the FB pin signal of the AC-DC chip, and inputs the FB pin signal exceeding the first preset value into the first comparator, and inputs the FB pin signal below the second preset value into the second comparator. The FB pin signal input to the second comparator is compared with the second reference value of the second comparator to obtain a second comparison result, and the second comparator output signal is sent to the FB short circuit detection module according to the comparison result; The FB short-circuit detection module sends an FB short-circuit detection output signal to the logic judgment module based on the second comparator output signal and the FB short-circuit detection signal. The short-circuit detection signal is generated synchronously when the internal drive signal of the AC-DC chip is issued. The logic judgment module sends a drive control signal to the main control logic module based on the FB short-circuit detection output signal. The main control logic module receives the over / under voltage output signal sent by the VDD over / under voltage protection module and the drive control signal, and controls the internal drive signal of the AC-DC chip based on the over / under voltage output signal and the drive control signal.

7. The method as described in claim 6, characterized in that, The internal drive signal of the AC-DC chip is controlled based on the over / under voltage output signal and the drive control signal, specifically as follows: When the VDD voltage exceeds the first preset voltage value, VDD is in an overvoltage state and sends a shutdown signal to the main control logic module, controlling the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the shutdown signal; When the VDD voltage value is lower than the second preset voltage value, VDD is in an undervoltage state and sends a power supply shutdown signal to the main control logic module, controlling the main control logic module to stop supplying power to the AC-DC chip after receiving the power supply shutdown signal; When the FB short-circuit detection signal is high and the negative voltage of the FB pin signal is less than the second preset value and greater than the second reference value for at least one cycle, the FB short-circuit detection output signal is high, the logic judgment module sends a drive shutdown signal to the main control logic module, and controls the main control logic module to shut down the internal drive signal of the AC-DC chip after receiving the drive shutdown signal. When the FB short-circuit detection signal is low and the FB pin signal has a negative voltage and is less than or equal to the second reference value for at least one cycle, the FB short-circuit detection output signal is low. The logic judgment module sends a drive hold signal to the main control logic module and controls the main control logic module to hold the internal drive signal of the AC-DC chip after receiving the drive hold signal.

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