Circuit for automatically unlocking NCP1252 overcurrent protection locking mode

Abstract

The utility model discloses a circuit for automatically unlocking an NCP1252 overcurrent protection locking mode. The circuit comprises a PWM controller chip U2 with the model of NCP1252, a timer chip U1 with the model of NE555, a filter capacitor C2, a decoupling capacitor C3 and a charging and discharging loop composed of a resistor R1, a resistor R2, a capacitor C1, a diode D1 and an N-channel MOS tube Q1. A pin 2, a pin 3 and a pin 6 of the U1 are connected with the charging and discharging loop, a pin 7 is connected with a pin 2 of the U2, and a pin 6 of the U2 is a PWM driving output end and is connected with a grid electrode of the Q1. And when overcurrent is detected, the U2 stops outputting and is locked, the Q1 is turned off, the voltage of the pin 2 and the pin 6 of the U1 is increased, the pin 7 of the U1 and the pin 2 of the U2 are turned to low levels, the U2 is unlocked, and the PWM waves are output again. The power supply system is simple in circuit design and low in cost, not only improves the automation degree of the power supply system, but also is wide in application scene and has important economic value.

Description

Technical Field

[0001] The utility model relates to the field of switching power supplies, in particular to a circuit for automatically unlocking an NCP1252 overcurrent protection lock mode. Background Art

[0002] The NCP1252 is a current-mode PWM controller chip commonly used in switching power supplies with forward and flyback topologies. Current-mode control offers faster response and better dynamic performance than traditional voltage-mode control by monitoring and regulating the inductor current in real time. In switching power supplies, current-mode controllers not only maintain output voltage stability but also provide precise current control and overcurrent protection. When an overcurrent condition is detected, the NCP1252 immediately shuts down output and enters latching mode to prevent damage to the circuit. However, this protection mechanism introduces some new challenges. In latching mode, the NCP1252 stops operating and does not automatically recover. It must be manually released by repowering or pulling down a specific pin, such as the BO pin. This approach is not ideal for power systems requiring automatic recovery, especially in unmanned or high-reliability applications, where manual reset is inconvenient and impractical.

[0003] To address the shortcomings of existing technologies, this utility model aims to provide a circuit that automatically unlocks and restores normal operation after the NCP1252 enters the overcurrent protection lock state. This circuit not only improves the power supply system's self-recovery capability and reduces manual intervention, but also enhances system stability and reliability, making it suitable for a wider range of application scenarios. Summary of the Invention

[0004] To achieve the above-mentioned purpose, the technical solution of the present invention is: a circuit for automatically unlocking the overcurrent protection lock mode of NCP1252, including a current mode PWM controller chip U2, an automatic unlocking chip U1, a filter capacitor C2, a decoupling capacitor C3 and a charge and discharge circuit composed of a resistor R1, a resistor R2, a capacitor C1, a diode D1, and an N-channel MOS tube Q1; the model of chip U2 is NCP1252, which is a current mode PWM controller chip for monitoring and controlling power supply output and providing overcurrent protection function; the model of chip U1 is NE555, which is a timer for generating a control signal to automatically unlock the overcurrent protection lock mode of NCP1252; the charge and discharge circuit is used to control the charging and discharging process of the voltage, generate the necessary control signal and combine with chip U1 to automatically unlock the overcurrent protection lock mode of NCP1252.

[0005] The technical effects of the present invention are as follows: First, the present invention simplifies the design and reduces costs by adding the NE555 timer chip and a small number of peripheral components, making it suitable for large-scale application and production. This circuit design does not require manual operation or repowering, and achieves automatic reset and unlocking through an additional control circuit, which greatly facilitates the maintenance and operation of the power supply system, especially in unmanned application scenarios, improving the reliability and automation of the system. Furthermore, the automatic unlocking function avoids the problem of long shutdowns caused by overcurrent protection lockout, allowing the power supply system to quickly resume normal operation, reducing equipment downtime caused by power failures, thereby improving the overall reliability and stability of the power supply system, and improving work efficiency and reducing costs. In addition, this technical solution is applicable to a variety of power supply topologies and can be widely used in consumer electronics, communication equipment, industrial control, electric vehicles and other fields. It is particularly suitable for power supply systems that require high reliability and automatic recovery functions. In short, the present invention improves the automation, reliability and safety of the power supply system through the circuit design of automatically unlocking the NCP1252 overcurrent protection lockout mode. The design is simple and effective, reduces costs, is applicable to a wide range of application scenarios, and has important economic value and practical significance. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] Figure 1 It is a circuit principle diagram of the utility model;

[0007] Figure 2 This is the internal functional structure diagram of NE555;

[0008] Figure 3 This is the NE555 pin voltage status diagram. DETAILED DESCRIPTION

[0009] The present invention will be further described below with reference to the accompanying drawings:

[0010] like Figure 1-3 As shown, the circuit for automatically unlocking the overcurrent protection lock mode of NCP1252 includes a current mode PWM controller chip U2, an automatic unlocking chip U1, a filter capacitor C2, a decoupling capacitor C3, and a charge and discharge circuit composed of a resistor R1, a resistor R2, a capacitor C1, a diode D1, and an N-channel MOS tube Q1;

[0011] The specific circuit connection is as follows: Pin 6-DRV of chip U2 is connected to the gate of N-channel MOS transistor Q1, Pin 2-BO of chip U2 is connected to Pin 7-DISCH of chip U1, Pin 1-GND of chip U1 is grounded, Pin 2-TRIG of chip U1 is respectively connected to Pin 6-THRES of chip U1, the drain of N-channel MOS transistor Q1, one end of resistor R1 and one end of capacitor C1, Pin 3-OUT of chip U1 is connected to the cathode of diode D1, Pin 4-RESET of chip U1 is connected to the positive power supply VCC, Pin 5-CONT of chip U1 is connected to one end of capacitor C2, the other end of capacitor C2 is grounded GND, Pin 8-VCC of chip U1 is connected to the positive power supply and one end of capacitor C3, the other end of capacitor C3 is grounded GND, the other end of capacitor C1 and the source of N-channel MOS transistor Q1 are connected to analog ground AGND, the other end of resistor R1 is respectively connected to one end of resistor R2 and the anode of diode D1, and the other end of resistor R2 is connected to the positive power supply VCC.

[0012] Chip U2, an NCP1252 current-mode PWM controller, monitors and controls the power supply output and provides overcurrent protection. It enters lockout mode when an overcurrent condition is detected and resumes normal operation after being unlocked by an external control signal.

[0013] The chip U1 is NE555, which is used as a timer to generate a control signal to help automatically unlock the overcurrent protection lock mode of NCP1252.

[0014] The main function of the charge-discharge circuit is to control the voltage charge and discharge process, thereby generating the necessary control signals and combining them with chip U1 to automatically unlock the NCP1252 overcurrent protection lock mode. Resistors R2 and R1 control the charge and discharge speed of the charge-discharge circuit and regulate voltage changes. Together with capacitor C1, they determine the charge and discharge time constants, affecting the output control signal timing of the NE555. Capacitor C1 acts as an energy storage element, controlling the voltage change of the charge-discharge circuit. It charges in the overcurrent protection lock state. When the voltage reaches the threshold, it triggers the NE555 to change its output state, and then discharges to restore the system to its initial state. Diode D1 prevents reverse current flow and protects circuit components. During the discharge process, it provides a unidirectional conduction path to ensure the correct current direction and prevent damage to components. N-channel MOS transistor Q1 acts as a switching element, controlling the conduction and cutoff of the charge-discharge circuit. Under the control signal of the NCP1252, it controls the charging and discharging process of capacitor C1, affecting the operating state of the circuit.

[0015] The working principle and working process of this utility model are as follows:

[0016] 1. Normal working status:

[0017] When NCP1252 is operating normally, U2's pin 6-DRV continuously outputs a PWM wave, turning on Q1 and C1's voltage is 0 V. At this point, the voltages on U1's pins 2-TRIG and 6-THRES are both less than 1 / 3 VCC, and U1's pin 7-DISCH and U2's pin 2-BO are high.

[0018] 2. Entering the overcurrent protection lock state:

[0019] When the NCP1252 detects an overcurrent condition, it automatically enters a locked state. U2's pin 6-DRV stops outputting PWM waveforms, Q1 turns off, and C1 begins charging through R1 and D1. As C1 charges, the voltage on U1's pin 2-TRIG and pin 6-THRES gradually rises. When the voltage exceeds 2 / 3 VCC, U1's pin 7-DISCH and U2's pin 2-BO flip to a low level, unlocking the NCP1252's overcurrent protection lockout mode.

[0020] 3. Automatic recovery work:

[0021] When the NCP1252 exits lock mode, U2's pin 6-DRV resumes outputting the PWM waveform, and the circuit enters normal operation. Q1 turns on again, and C1 discharges through R1 and D1. As C1 discharges, the voltages on U1's pins 2-TRIG and 6-THRES drop below 1 / 3 VCC. U1's pin 7-DISCH and U2's pin 2-BO flip to high levels, and the system returns to normal.

Claims

1. A circuit for automatically unlocking the NCP1252 overcurrent protection lock mode, characterized in that: It includes a current-mode PWM controller chip U2, an automatic unlocking chip U1, a filter capacitor C2, a decoupling capacitor C3, and a charge-discharge circuit consisting of a resistor R1, a resistor R2, a capacitor C1, a diode D1, and an N-channel MOS tube Q1; the chip U2 model is NCP1252, which is a current-mode PWM controller chip used to monitor and control power supply output and provide overcurrent protection function; the chip U1 model is NE555, which is used as a timer to generate a control signal and automatically unlock the overcurrent protection lock mode of NCP1252; the charge-discharge circuit is used to control the charging and discharging process of the voltage, generate the necessary control signal and combine with chip U1 to automatically unlock the overcurrent protection lock mode of NCP1252.

2. The circuit for automatically unlocking the NCP1252 overcurrent protection lock mode according to claim 1, characterized in that: The specific connections of the circuit are as follows: pin 6-DRV of chip U2 is connected to the gate of N-channel MOS transistor Q1, pin 2-BO of chip U2 is connected to pin 7-DISCH of chip U1, pin 1-GND of chip U1 is grounded, pin 2-TRIG of chip U1 is respectively connected to pin 6-THRES of chip U1, the drain of N-channel MOS transistor Q1, one end of resistor R1 and one end of capacitor C1, pin 3-OUT of chip U1 is connected to the cathode of diode D1, pin 4-RESET of chip U1 is connected to the positive power supply VCC, pin 5-CONT of chip U1 is connected to one end of capacitor C2, the other end of capacitor C2 is grounded GND, pin 8-VCC of chip U1 is connected to the positive power supply and one end of capacitor C3, the other end of capacitor C3 is grounded GND, the other end of capacitor C1 and the source of N-channel MOS transistor Q1 are connected to analog ground AGND, the other end of resistor R1 is respectively connected to one end of resistor R2 and the anode of diode D1, and the other end of resistor R2 is connected to the positive power supply VCC.

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