An output short-circuit current limiting circuit and a switching power supply

Abstract

This invention relates to the field of switching power supply technology, specifically to an output short-circuit current limiting circuit and a switching power supply. The circuit includes a current detection unit, a comparison unit, a power chip, a timing unlocking unit, and a soft-start unit. Through the cooperation of the timing unlocking unit and the soft-start unit, when a short circuit occurs at the switching power supply output, the power supply performs periodic detection of the short-circuit fault with a minimum duty cycle current. This ensures that the system can perform periodic restart detection of the short circuit on time, while effectively reducing the peak and effective values ​​of the short-circuit current in the power supply circuit, thereby reducing power consumption and overheating risk, and mitigating or even eliminating noise generated by periodic restarts. Simultaneously, after the short-circuit fault in the circuit is cleared, the soft-start unit can control the power supply to soft-start in an incremental manner, thereby reducing the inrush current in the circuit and achieving circuit protection.

Description

Technical Field

[0001] This invention relates to the field of switching power supply technology, specifically to an output short-circuit current limiting circuit and a switching power supply. Background Technology

[0002] In industrial applications (such as industrial vehicles), switching power supplies often require constant current output when short-circuited. Typically, the maximum short-circuit constant current is 1.2 times the rated current, resulting in higher power consumption under short-circuit constant current conditions compared to full-load operation. Simultaneously, concentrated losses can cause some components to overheat. If the power supply remains in a short-circuit constant current state for an extended period, there is a risk of overheating and failure.

[0003] Prior art CN 113848785 B discloses a switching current output circuit, including an MCU (microcontroller unit), intermediate circuits, and an output device, used for drive control of the load with at least two levels of current protection. The MCU outputs a control signal and a hiccup control signal (a square wave signal of a preset frequency) in real time. The control signal keeps the circuit in normal operating mode, while the hiccup control signal triggers a current limiting protection mode during overcurrent, causing the output device (such as the first MOSFET Q1) to alternately turn off and on, entering a periodic hiccup mode. After the overcurrent fault is cleared, the circuit automatically recovers to normal operating mode based on voltage changes, realizing a self-recovery function.

[0004] However, in the actual hiccup control process, due to the existence of short circuit faults, the power circuit will generate a large current surge every time it restarts. This will not only generate electrical noise and mechanical vibration, affecting sensitive loads, but the frequent surges of large current will also lead to a decrease in the lifespan of electrical components. Summary of the Invention

[0005] To address the technical problem of large current surge during hiccup mode restart in existing technologies, this application provides an output short-circuit current limiting circuit, comprising: A current detection unit is used to collect the output current of the power supply circuit. The comparison unit is used to calculate the real-time state voltage based on the output current and compare the real-time state voltage with the reference voltage. A power supply chip is used to control the current in a power supply circuit. A timing unlocking unit is used to lock the in-phase input voltage of the comparison unit during the detection cycle; A soft-start unit is used to control the duty cycle of the power chip; When the real-time state voltage is greater than the reference voltage, the comparison unit controls the power chip to stop working, the timing unlocking unit starts timing the detection cycle, and locks the non-inverting input of the comparison unit to a high level during the detection cycle. When the real-time state voltage is less than or equal to the reference voltage, the soft-start unit compares the duty cycle of the power chip with the system's required duty cycle. If the duty cycle of the power chip is less than the system's required duty cycle, the soft-start unit increases the duty cycle of the power chip sequentially according to the interval duty cycle. At the end of the detection cycle, the timing unlocking unit sets the non-inverting input of the comparison unit to a low level, so that the soft-start unit controls the power chip to operate at the lowest duty cycle.

[0006] The present invention also provides a switching power supply, including the above-described output short-circuit current limiting circuit.

[0007] The technical effects and advantages of this invention are as follows: The output short-circuit current limiting circuit provided by this invention, through the cooperation of a timing unlocking unit and a soft-start unit, limits the short-circuit current in the circuit by controlling the duty cycle of the power supply when a short circuit occurs at the output of the switching power supply. This allows the power supply to complete the periodic detection of short-circuit faults with the minimum duty cycle current. While ensuring that the system can perform periodic restart detection of short circuits on time, it can also effectively reduce the peak and effective values ​​of the short-circuit current in the power supply circuit, thereby reducing power consumption and overheating risk, and mitigating or even eliminating noise caused by periodic restarts. Simultaneously, after the short-circuit fault in the circuit is cleared, the soft-start unit can control the power supply to soft-start in an incremental manner, thereby reducing the inrush current in the circuit and achieving circuit protection. Attached Figure Description

[0008] Figure 1 This is a schematic diagram of the overall structure of the circuit provided by the present invention.

[0009] Figure 2 This is an electrical schematic diagram of an embodiment of the timing unlocking unit of the present invention. Detailed Implementation

[0010] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0011] refer to Figure 1 This invention provides an output short-circuit current limiting circuit, which can limit the peak value of the short-circuit current in the power supply circuit when the output of the switching power supply is short-circuited, thereby protecting the circuit and reducing power consumption during short circuits. The circuit specifically includes a current detection unit, a comparison unit, a power chip, a timing unlocking unit, and a soft-start unit.

[0012] The current detection unit is used to acquire the output current of the power supply circuit. The comparison unit is used to calculate the output voltage based on the output current and compare the output voltage with a reference voltage. The power chip is used to control the power supply circuit based on the comparison result output by the comparison unit. The timing unlock unit is used to periodically control the in-phase input voltage of the comparison unit based on the comparison result output by the comparison unit. The soft-start unit is used to gradually increase the duty cycle of the power chip when a low level is received from the comparison unit to achieve soft-start of the power supply.

[0013] The current detection unit is electrically connected to the non-inverting input of the comparator unit. The current detection unit samples the output current Iamp of the power supply circuit in real time and transmits the detected output current Iamp to the non-inverting input of the comparator unit. The inverting input of the comparator unit is connected to the reference voltage REF, and calculates the real-time state voltage of the power supply circuit based on the output current Iamp. The real-time state voltage is then compared with the reference voltage REF. The output of the comparator unit is electrically connected to the input of the soft-start unit, the CS pin of the power supply chip, and the timing unlock unit. The output of the timing unlock unit is connected to the non-inverting input of the comparator unit, and the output of the soft-start unit is electrically connected to the COMP pin of the power supply chip.

[0014] When a short-circuit current exists in the power supply circuit, if the real-time state voltage calculated based on the output current Iamp is greater than the reference voltage REF, the comparator unit outputs a high level to the CS pin of the power chip and the timing unlock unit. The power chip enters cycle-by-cycle current limiting mode, with a duty cycle of 0, controlling the power supply to stop outputting current to the power circuit. Simultaneously, the timing unlock unit receives the high level output from the comparator unit, begins the detection cycle timing, locks the voltage at the non-inverting input of the comparator unit, keeps the comparator unit outputting a high level, and thus keeps the power chip in a state with a duty cycle of 0 during the detection cycle.

[0015] After the detection cycle ends, the timing unlock unit sets the non-inverting input of the comparator unit to a low level, causing the comparator unit to output a low level to the CS pin of the power chip, thus starting the power chip and supplying power to the power circuit. Simultaneously, the soft-start unit receives the low level from the comparator unit and first pulls the duty cycle of the power chip low, allowing it to start operating at the lowest duty cycle. The current detection unit continues to sample the output current Iamp of the power circuit. If a short circuit still exists in the power circuit, the comparator unit outputs a high level again, the power chip stops operating again, and the timing unlock unit enters a new detection cycle. This process repeats until the short circuit fault in the power circuit is cleared and the current detection unit detects that the current in the power conversion circuit has returned to normal. When there is no short circuit in the power circuit, the real-time state voltage calculated based on the output current Iamp is less than the reference voltage REF. The comparator unit outputs a low level to the CS pin of the power chip and the input of the soft-start circuit. The power chip gradually increases its duty cycle from the lowest duty cycle until it reaches the system's required duty cycle. The power circuit then begins to supply power to the power conversion circuit stably and normally, ensuring the stable operation of the entire circuit system. By combining the timing unlocking unit and the soft-start unit, the peak output current is limited and the short-circuit current surge is reduced when short-circuit protection is performed in hiccup mode. This not only effectively protects the circuit from the impact of short-circuit current, but also further reduces the power consumption of the circuit during short circuits, as well as the electrical noise and mechanical vibration caused by frequent restarts.

[0016] Specifically, the comparison unit can use a high-speed comparator to implement the voltage comparison function, which is existing technology and will not be elaborated here.

[0017] Generally, in order to reduce circuit costs, the timing function of the timing unlocking unit can be implemented in hardware, such as through an RC charging circuit, and using a switching transistor to control the discharge of the capacitor. When the voltage of the timing capacitor is greater than the conduction voltage of the switching transistor, the timing capacitor is grounded to the non-inverting input of the comparator, thereby realizing the periodic reset of the timing unlocking unit and the periodic control of the power supply startup.

[0018] Specifically, refer to Figure 2 The timing unlocking unit includes: a first switch Q1, a second switch Q2, a third switch Q3, a timing capacitor C1, and a first resistor R1. The control terminal of the first switch Q1 is connected to the output terminal of the comparator unit, and its first power terminal is connected to the control power supply VCC. The second power terminal is connected to the first terminal of the timing capacitor C1 through the first resistor R1. The second terminal of the timing capacitor C1 is connected to the control terminal of the second switch Q2. The first power terminal of the second switch Q2 is grounded. The second power terminal is connected to the control terminal of the third switch Q3 and the control power supply VCC. The first power terminal of the third switch Q3 is connected to the output terminal of the comparator unit, and its second power terminal is connected to the non-inverting input terminal of the comparator unit.

[0019] When the comparator outputs a high level, the first switch Q1 is turned on, and the control power supply VCC charges the timing capacitor C1, starting the detection cycle. At this time, the control terminal voltage of the second switch Q2 is lower than the conduction threshold, and the control terminal voltage of the third switch Q3 is determined by the control power supply VCC and is greater than its conduction threshold, so the third switch Q3 is turned on. The output terminal of the comparator is directly connected to the non-inverting input terminal, keeping the non-inverting input terminal always at a high level. When the voltage of the timing capacitor C1 rises above the conduction threshold of the second switch Q2, the second switch Q2 is turned on, grounding the control terminal of the third switch Q3, turning off the third switch Q3. Simultaneously, the timing capacitor C1 begins to discharge. The voltage at the non-inverting input terminal of the comparator is determined by the output current Iamp sampled by the current detection unit, detecting whether a short circuit fault still exists in the power supply circuit.

[0020] When the comparator outputs a low level, the first switch Q1 is not turned on, and the entire timing and unlocking circuit does not work.

[0021] The first switch Q1, the second switch Q2, and the third switch Q2 can be implemented using either MOSFETs or transistors. When using a MOSFET, the control terminal is the gate, and the first and second power terminals are the source and drain, respectively. When using a transistor, the control terminal is the base, and the first and second power terminals are the emitter and collector, respectively.

[0022] However, since the detection cycle of a hardware-implemented timing unlock unit is fixed, it is difficult to adapt to complex and ever-changing application scenarios. Therefore, the timing function of the timing unlock unit can also be implemented in software. For example, the timing unlock unit can use a MOSFET connected to an MCU controller to control the charging and discharging of its internal capacitor, thereby achieving an adjustable detection cycle and improving adaptability to different scenarios. Another advantage of using a MOSFET to control the timing unlock unit is that when a short-circuit fault in the circuit is cleared, the MCU controller can force the exit from the detection cycle, causing the power supply to restart immediately and respond promptly to load requirements.

[0023] To improve adaptability to complex environments, the timing unlocking unit can use a MOSFET connected to the MCU controller to implement the timing function, allowing the detection cycle to be adjusted via software. Specifically, the detection cycle can be adjusted in the following ways: S21. When the comparison unit first sends a high level, the timing unlock unit starts timing the detection cycle and starts counting the cycles. The duration of the detection cycle can be calculated according to the following formula: T_te=n*T_ba In the formula, n is the number of detection cycles within this short-circuit fault, and T_ba is the base cycle duration.

[0024] S22. When the comparison unit outputs a low level, the cycle count is set to 1.

[0025] When a short circuit fault occurs in the power supply circuit, the timing unlocking unit begins periodic short circuit fault detection at detection cycles. The duration of the first detection cycle is the base cycle duration. After the detection cycle ends, the power chip restarts and checks if a short circuit fault still exists in the power supply circuit. If it still exists, it indicates that the short circuit fault may be difficult to eliminate, and the detection cycle is extended. The extension rule is the number of detection cycles executed multiplied by the base cycle duration. That is, the more detection cycles executed, the more difficult it is to eliminate the short circuit fault. Therefore, it is unnecessary to perform fault detection frequently, reducing the short circuit fault detection frequency, which can effectively reduce power consumption during a short circuit.

[0026] When a short circuit fault in the power supply circuit is cleared, or when the current in the power supply circuit is detected to be less than the short circuit current, the timing unlocking unit clears the count of the detection cycle. This allows the fault detection and restart to begin again with the reference cycle duration when a short circuit fault occurs again. This ensures that the system can respond quickly when a short circuit fault occurs again, making the short circuit protection more flexible and improving its adaptability to complex and ever-changing power environments.

[0027] Specifically, the baseline detection period can be set between 0.1 seconds and 0.5 seconds, which is the standard setting for a hiccup cycle. The baseline detection period can also be set to a longer time as needed.

[0028] Specifically, the minimum duty cycle of the power chip can be set to the shortest current pulse length that the high-speed comparator can recognize. When the timing unlocking unit contacts the lock of the power chip, the power chip controls the power supply to send a short current pulse to the power circuit. The high-speed comparator uses this current pulse to determine whether there is still a short circuit fault in the power circuit. If there is, the short circuit protection continues. If not, the soft start unit increases the duty cycle of the power chip according to the interval duty cycle and sends another current pulse to the power circuit. This step is repeated until the duty cycle of the power chip reaches the system's required duty cycle, thus completing the power supply startup.

[0029] In the above process, the duty cycle (Duty) of the power supply chip can be calculated using the following formula: Duty = m * Du_da + Du_ba In the formula, m is the number of pulse currents emitted by the power supply circuit after eliminating the short circuit fault, Du_da is the interval duty cycle, and Du_ba is the minimum duty cycle.

[0030] In the above steps, the duty cycle determines the power supply's startup speed. When the power supply starts with the minimum duty cycle, it supplies power to the circuit in pulses. The high-speed comparator circuit detects that the voltage in the circuit is lower than the reference voltage and sends a low-level pulse to the soft-start circuit. The soft-start circuit adjusts the duty cycle for each low-level pulse received. For circuits with a fixed PWM pulse frequency, each PWM cycle is fixed, but the duration of each pulse is different and related to the duty cycle. To ensure the switching power supply's response time to the load, the duty cycle needs to be adjusted based on the system's required duty cycle and the minimum duty cycle. When the interval duty cycle is large, fewer pulses are needed to achieve the system's required duty cycle, thus shortening the response time to the load. When the interval duty cycle is small, more pulses are needed to achieve the system's required duty cycle, thus extending the system's response time to the load.

[0031] In summary, if it is necessary to ensure that the response time of the switching power supply to the load remains constant, the interval duty cycle can be set as the difference between the system demand duty cycle and the minimum duty cycle, divided by the load response time. When the system demand duty cycle is large, the interval duty cycle is large; when the system demand duty cycle is small, the interval duty cycle is small. This ensures that the system response time to the load remains constant and guarantees the stability of system performance.

[0032] Specifically, the duty cycle can be set to a fixed value, thereby maintaining a fixed starting characteristic of the power supply, which is more conducive to reducing the impact of the starting current on electrical components and extending the service life of the circuit.

[0033] If a high-speed comparator is used in the comparison unit, its extremely fast response speed, capable of responding to pulse currents of several hundred nanoseconds, allows it to determine the presence of a short-circuit current within a single PWM current pulse cycle. When the timing unlock unit pulls down the voltage at the non-inverting input of the comparator, the high-speed comparator outputs a low level to the power chip and soft-start unit, activating the power chip. The soft-start unit controls the power chip to supply power to the power circuit with a lower duty cycle, i.e., the power supply sends a short pulse current to the power circuit. The current detection unit samples this pulse current and transmits it to the high-speed comparator. The high-speed comparator determines whether a short-circuit fault exists based on the received short pulse current. If a short-circuit fault exists, it sends a high level to the power chip and soft-start unit, stopping the power supply. If no short-circuit fault exists, the soft-start circuit continues to increase the duty cycle of the power chip, which then controls the power supply to send a pulse current with an even higher duty cycle to the circuit, again detecting the presence of a short-circuit fault. By repeatedly performing the above steps, when a short-circuit current exists in the circuit, periodic short-circuit detection and restart are achieved with an extremely low duty cycle. Once the short-circuit fault is cleared, the duty cycle of the power supply chip is gradually increased until the required system duty cycle is reached, thus achieving soft-start of the power supply. This reduces the output current during a short circuit while providing short-circuit protection for the switching power supply, thereby reducing the power consumption required for short-circuit restart and avoiding the risk of overheating.

[0034] Specifically, the system duty cycle requirement refers to the duty cycle transmitted by the vehicle's main controller when the switching power supply is operating normally.

[0035] The present invention also provides a switching power supply, including the above-described output short-circuit current limiting circuit.

[0036] In summary, the output short-circuit current limiting circuit provided by this invention, through the cooperation of a timing unlocking unit and a soft-start unit, limits the short-circuit current in the circuit by controlling the duty cycle of the power supply when a short circuit occurs at the output of the switching power supply. This allows the power supply to complete periodic detection of short-circuit faults with a minimum duty cycle. While ensuring that the system can perform periodic restart detection of short circuits on time, it can also effectively reduce the peak and effective values ​​of the short-circuit current in the power supply circuit, thereby reducing power consumption and overheating risk, and mitigating or even eliminating noise caused by periodic restarts. Simultaneously, after the short-circuit fault in the circuit is cleared, the soft-start unit can control the power supply to soft-start in an incremental manner, thereby reducing the inrush current in the circuit and achieving circuit protection.

[0037] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. An output short-circuit current limiting circuit, characterized in that, include The current detection unit is used to collect the output current of the power supply circuit. The comparison unit is used to calculate the real-time state voltage based on the output current and compare the real-time state voltage with the reference voltage. Power supply chip, used to control the output current of the power supply; A timing unlocking unit is used to lock the in-phase input voltage of the comparison unit during the detection cycle; A soft-start unit is used to control the duty cycle of the power chip; When the real-time state voltage is greater than the reference voltage, the comparison unit controls the power chip to stop working, the timing unlocking unit starts timing the detection cycle, and locks the non-inverting input of the comparison unit to a high level during the detection cycle. When the real-time state voltage is less than or equal to the reference voltage, the soft-start unit compares the duty cycle of the power chip with the system's required duty cycle. If the duty cycle of the power chip is less than the system's required duty cycle, the soft-start unit increases the duty cycle of the power chip sequentially according to the interval duty cycle. At the end of the detection cycle, the timing unlocking unit sets the non-inverting input of the comparison unit to a low level, so that the soft-start unit controls the power chip to operate at the lowest duty cycle.

2. The circuit according to claim 1, characterized in that, The timing unlocking unit includes: The first switching transistor has its control terminal connected to the output terminal of the comparison unit and its first power terminal connected to the control power supply. A timing capacitor, the first end of which is connected to the second power terminal of the first switching transistor; The second switching transistor has its control terminal connected to the second terminal of the timing capacitor, and its first power terminal grounded. The third switching transistor has its control terminal connected to both the second power terminal of the second switching transistor and the control power supply. Its first power terminal is connected to the output terminal of the comparator unit, and its second power terminal is connected to the non-inverting input terminal of the comparator unit.

3. The circuit according to claim 2, characterized in that, The timing unlocking unit also includes a first resistor connected in series between the timing capacitor and the second power terminal of the first switching transistor.

4. The circuit according to claim 1, characterized in that, The input terminal of the soft-start circuit is connected to the output terminal of the comparator unit, and the output terminal of the soft-start circuit is connected to the COMP pin of the power chip. When the input terminal of the soft-start circuit receives a high level, the soft-start circuit adjusts the duty cycle of the power chip to zero. When the input terminal of the soft-start circuit receives a low level, the soft-start circuit gradually increases the duty cycle of the power chip.

5. A switching power supply, characterized in that, Includes the circuit described in any one of claims 1 to 4.

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