An overcurrent protection circuit with adjustable overcurrent time

Abstract

This utility model relates to the field of switching power supply technology, and in particular to a protection circuit with adjustable overcurrent time. It includes a current sampling module for sampling the output current and converting it into a voltage signal I_OCP; a delay circuit module including resistor R83 and capacitor C51 for delaying the overcurrent time through the charging and discharging process; and a reference voltage source for providing a reference voltage VREF. A control logic module includes comparator U1-B, whose input is connected to the delay circuit module and the reference voltage source. It compares the delayed voltage signal I_OCP with the reference voltage VREF and outputs a control signal to turn off the DC-DC converter based on the control signal. This overcurrent time-adjustable protection circuit controls the on and off times of maximum output power through a charging and discharging delay circuit using operational amplifiers, diodes, resistors, and capacitors. The control logic is simple, low-cost, and highly reliable.

Description

Technical Field

[0001] This utility model relates to the field of switching power supply technology, and in particular to a protection circuit with adjustable overcurrent time. Background Technology

[0002] With the development of switching power supply technology, high power density and high efficiency have become the trend. However, existing secondary overcurrent protection schemes have shortcomings: when there is an overcurrent or short circuit, the output current increases, exceeding the overcurrent point setting, resulting in excessive current stress on the power switching transistors, which may damage the devices. Traditional methods use current-limiting resistors to sample the current, convert it into a voltage signal, and then compare it through an amplification circuit to put the DC-DC converter into a constant current state, limiting the output current. However, as the load increases, the output voltage decreases, and the stress on the secondary side of the power supply increases. If the converter operates in a low-voltage, high-current mode for a long time, the losses of switching and magnetic components increase, leading to the risk of power supply failure. Utility Model Content

[0003] To address the problem of long-term low-voltage, high-current operation causing losses in existing secondary overcurrent protection systems, this invention provides a protection circuit with an adjustable overcurrent time. This circuit uses an RC delay circuit to charge and discharge the I_OCP signal, controlling the switching time. The adjustable overcurrent time extends the operating time to provide more energy during mild overloads and shortens the time to reduce device stress during severe overloads, protecting power switching transistors and magnetic components, and improving product reliability.

[0004] This utility model provides a protection circuit with an adjustable overcurrent time, including... The current sampling module is used to sample the output current and convert it into a voltage signal I_OCP. The delay circuit module, connected to the current sampling module, includes resistor R83 and capacitor C51. It is used to achieve overcurrent time delay during the charging and discharging process. The charging path consists of resistor R83, diode D20, and capacitor C51, while the discharging path consists of capacitor R71, diode D24, and capacitor C51. A reference voltage source is used to provide the reference voltage VREF. The control logic module includes a comparator U1-B. The input of the comparator U1-B is connected to the delay circuit module and the reference voltage source. It is used to compare the delayed voltage signal with the reference voltage and output a control signal to turn off the DC-DC converter according to the control signal.

[0005] When the output current increases, the I_OCP voltage increases linearly and proportionally with the output current. By setting a time, the circuit compares the I_OCP voltage with the reference voltage VREF via comparator U1-B to determine whether to turn off the DC-DC converter. Under mild overload conditions, where the I_OCP voltage is slightly greater than the reference voltage VREF, the delay circuit module will delay for a pre-set time. During this delay, the circuit will not immediately turn off the DC-DC converter but will extend its operating time to provide more energy to the load. This design can, to some extent, meet the operating requirements of loads with fluctuating energy demands, improving the circuit's adaptability and flexibility. Under severe overload conditions, where the I_OCP voltage is much greater than the reference voltage VREF, the delay time of the delay circuit module will be shortened accordingly. This is to quickly turn off the DC-DC converter within a short time, reducing the stress on the power switching transistors and magnetic components, and minimizing damage caused by overcurrent. In this way, critical components in the circuit can be effectively protected, improving product reliability and lifespan. Furthermore, this protection circuit is adjustable. Users can flexibly adjust the parameters of resistor R83 and capacitor C51 in the delay circuit module according to the actual application scenario and load requirements, thereby achieving precise setting of the overcurrent time.

[0006] Furthermore, one end of resistor R83 is connected to the voltage signal I_OCP, and the other end is connected to capacitor C51 through diode D20. The other end of capacitor C51 is grounded. One end of resistor R71 is connected to the voltage signal I_OCP, and the other end is connected to the cathode of diode D24. The anode of diode D24 is connected to the inverting input pin 6 of comparator U1-B.

[0007] Furthermore, the reference voltage VREF is grounded through resistors R50 and R47 connected in series, and the non-inverting input pin 5 of comparator U1-B is connected to the node of resistors R50 and R47. Voltage division through resistors R50 and R47 provides a stable reference potential for the non-inverting input pin 5 of comparator U1-B.

[0008] Furthermore, the non-inverting input pin 5 of comparator U1-B is connected to resistor R39 via diode D12. The other end of resistor R39 is connected to output pin 7 of comparator U1-B, and the other end of output pin 7 is connected to the control signal. This creates a feedback loop. Diode D12 prevents reverse current, ensuring unidirectional signal transmission, so that the signal output from output pin 7 of comparator U1-B can reach the non-inverting input pin 5 in a predetermined direction via resistor R39.

[0009] Furthermore, the reference voltage source includes an adjustable regulator U10 for stabilizing the reference voltage. The supply voltage VCC is connected to the positive pin 2 of the adjustable regulator U10 through resistor R44, and the negative pin 3 of the adjustable regulator U10 is grounded. Resistors R45 and R46 are connected in series between the positive and negative pins of the adjustable regulator U10. The reference pin 1 of the adjustable regulator U10 is connected to the node of resistors R45 and R46. A capacitor C45 is connected between the positive and negative pins of the adjustable regulator U10, with one end of capacitor C45 connected to the reference voltage VREF and the other end grounded. The adjustable regulator U10 uses an AZ431AN and can provide a stable and reliable reference voltage for the circuit.

[0010] Furthermore, the current sampling module includes operational amplifier U1-A. The non-inverting input pin 3 of operational amplifier U1-A is connected to the current signal AGND through resistor R49. The node between resistor R49 and the current signal AGND is grounded through capacitor C40. The inverting input pin 2 of operational amplifier U1-A is connected to the current signal CURRENT- through resistor R48. The node between resistor R48 and the current signal CURRENT- is grounded through capacitor C38. A capacitor C37 is connected between the non-inverting input pin 3 and the inverting input pin 2 of operational amplifier U1-A. The positive power supply pin 8 of operational amplifier U1-A is connected to the supply voltage VCC. The negative power supply pin 4 of operational amplifier U1-A is grounded. The output pin 1 of operational amplifier U1-A outputs the voltage signal I_OCP. A capacitor C34 is connected between the positive power supply pin 8 and the output pin 1 of operational amplifier U1-A. A capacitor C35 is connected between the inverting input pin 2 and the output pin 1. A resistor R38 is connected in parallel across capacitor C35. The current sampling module can accurately sample and process the current signal. The operational amplifier U1-A plays a key role in signal amplification and conversion, converting the input current signal into a voltage signal I_OCP that can be used for subsequent circuit processing.

[0011] The beneficial effects of this utility model are as follows: This invention provides a protection circuit with an adjustable overcurrent protection time. It controls the on / off time of maximum output power through a charging / discharging delay circuit using an operational amplifier, diodes, resistors, and capacitors. The control logic is simple, low-cost, and highly reliable. The adjustable overcurrent protection time circuit effectively protects power devices and magnetic core devices from prolonged overpower failure. When the output current increases, the I_OCP voltage increases linearly proportionally to the output current. By setting the adjustable time, a comparator compares the voltage with a reference voltage VREF to determine whether to turn off the DC-DC converter. This avoids the risk of power device and magnetic device failure due to prolonged overload operation of the DC-DC converter under long-term constant current conditions, thus improving product reliability. Attached Figure Description

[0012] To more clearly illustrate the specific embodiments of this utility model or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this utility model. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Figure 1 This is an overcurrent protection circuit diagram; Detailed Implementation

[0013] The technical solution of this utility model will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are some embodiments of this utility model, but not all embodiments.

[0014] To effectively protect power devices and prevent power switches and magnetic components from failing under prolonged overpower conditions, a protection circuit with adjustable overcurrent time is designed, such as... Figure 1 As shown, the system includes a current sampling module for sampling the output current and converting it into a voltage signal I_OCP; a delay circuit module connected to the current sampling module, including resistor R83 and capacitor C51, used to achieve overcurrent time delay through the charging and discharging process, with resistor R83, diode D20, and capacitor C51 forming the charging path, and capacitor R71, diode D24, and capacitor C51 forming the discharging path; a reference voltage source for providing a reference voltage VREF; and a control logic module including comparator U1-B, whose input is connected to the delay circuit module and the reference voltage source, used to compare the delayed voltage signal with the reference voltage and output a control signal to turn off the DC-DC converter according to the control signal.

[0015] When the output is overcurrent or short-circuited, the output current will increase as the output voltage decreases. The short-circuit current often exceeds the setting of the overcurrent point, and the current stress on the power switch tube will be very large, which may damage the power device. To reduce the current stress on the power tube and meet the requirements of output short-circuit protection, it is necessary to limit the current magnitude when the output is overcurrent. The overcurrent time can be set in the protection circuit to achieve overcurrent time delay by adjusting the voltage level. The on and off times of the maximum output power are controlled by the charge and discharge delay circuit of the operational amplifier, diode, resistor, and capacitor. The control logic is simple, the cost is low, and the reliability is high. The overcurrent protection time can be set in the circuit to control the working time under different overload conditions. Under the condition that the overload of the rated power is not serious, more output energy can be provided to ensure the operation of the subsequent load device. When the load seriously exceeds the standard, the sampling voltage of I_OCP will linearly increase as the current increases. The faster the rising slope of the reference voltage VREF at pin 6 of U1-B reaches through the time setting circuit of resistor R83 and capacitor C51, the shorter the working time of the DC-DC converter under the overload condition. While providing peak power, the stress on the power device and magnetic device is effectively reduced, and the reliability of the product is improved.

[0016] Under normal conditions (no overcurrent), the output current is converted into a voltage through R48 and R49. U1-A is configured as a unity-gain buffer and outputs the voltage signal I_OCP. The reference voltage source TL431 generates a stable VREF = 2.5V by dividing the voltage through R44 and R45. The voltage of capacitor C51 (close to 0V) < VREF, making the output of U1-B high level, and the DC-DC operates normally; in the light overload state, the voltage of I_OCP slowly charges capacitor C51 through resistor R83 and diode D20. The charging time constant τ = R83 × C51, which supports the short-time startup requirements of loads such as motors; in the serious short-circuit state, the voltage of capacitor C51 rises rapidly. The voltage of capacitor C51 > VREF, making the output of U1-B low level, and the DC-DC stops operating. Capacitor C51 discharges through R71. When the voltage of capacitor C51 discharges to < VREF, the output of U1-B resumes high level, and the DC-DC restarts. An adaptive mechanism for faster protection under more serious overcurrent is achieved by controlling the RC charging rate through voltage.

[0017] One end of resistor R83 is connected to the voltage signal I_OCP, and the other end is connected to capacitor C51 through diode D20. The other end of capacitor C51 is grounded; one end of resistor R71 is connected to the voltage signal I_OCP, and the other end is connected to the cathode of diode D24. The anode of diode D24 is connected to the inverting input pin 6 of comparator U1-B.

[0018] The voltage signal I_OCP charges capacitor C51 through resistor R83 and diode D20. The charging process of capacitor C51 is affected by the resistance value of resistor R83; the larger the resistance value, the longer the charging time, thus changing the delay time of the delay circuit module. The capacitance value of capacitor C51 also affects the charging speed; a larger capacitance value increases the charging time, thereby extending the delay time. By controlling the charging process of capacitor C51 in this way, the delay time during overcurrent can be flexibly adjusted to adapt to different load requirements and application scenarios.

[0019] The reference voltage VREF is grounded through resistors R50 and R47 connected in series. The non-inverting input pin 5 of comparator U1-B is connected to the node of resistors R50 and R47. This configuration allows the reference voltage VREF to be divided by resistors R50 and R47, providing a stable reference potential for the non-inverting input pin 5 of comparator U1-B.

[0020] The non-inverting input pin 5 of comparator U1-B is connected to resistor R39 via diode D12. The other end of resistor R39 is connected to output pin 7 of comparator U1-B, and the other end of output pin 7 is connected to a control signal. This creates a feedback loop. Diode D12 prevents reverse current, ensuring unidirectional signal transmission, so that the signal output from output pin 7 of comparator U1-B can reach the non-inverting input pin 5 in a predetermined direction via resistor R39.

[0021] Resistor R39 limits the current and divides the voltage of the signal, adjusting the strength of the feedback signal to prevent excessively large signals from damaging or affecting the normal operation of comparator U1-B. When the control signal is high, output pin 7 of comparator U1-B outputs a high level. This high-level signal is fed back to the non-inverting input pin 5 through resistor R39 and diode D12, increasing the potential of the non-inverting input pin 5. This makes it easier for comparator U1-B to output a high level during comparison, enhancing the stability and response speed of the circuit. Conversely, when the control signal is low, output pin 7 outputs a low level, and the signal fed back to the non-inverting input pin 5 lowers its potential, making it easier for comparator U1-B to output a low level, adapting to different operating states.

[0022] The reference voltage source includes an adjustable regulator U10 for stabilizing the reference voltage. The supply voltage VCC is connected to the positive pin 2 of the adjustable regulator U10 through resistor R44. The negative pin 3 of the adjustable regulator U10 is grounded. Resistors R45 and R46 are connected in series between the positive and negative pins of the adjustable regulator U10. The reference pin 1 of the adjustable regulator U10 is connected to the node of resistors R45 and R46. Capacitor C45 is connected between the positive and negative pins of the adjustable regulator U10. One end of capacitor C45 is connected to the reference voltage VREF, and the other end is grounded.

[0023] The adjustable voltage regulator U10 uses an AZ431AN, providing a stable and reliable reference voltage for the circuit. In actual operation, the supply voltage VCC provides a suitable voltage to the positive pin 2 of the adjustable voltage regulator U10 via resistor R44. Resistor R44 limits current, preventing excessive current from damaging the adjustable voltage regulator U10. By adjusting the resistance ratio of resistors R45 and R46, the magnitude of the reference voltage can be precisely adjusted to meet the requirements of different circuits. Capacitor C45 acts as a filter, effectively filtering out high-frequency noise and ripple in the power supply, ensuring the stability and purity of the reference voltage VREF. When the power supply voltage fluctuates or interference exists in the circuit, capacitor C45 can respond quickly, absorbing or releasing charge to keep the reference voltage VREF near the set stable value. This reference voltage source design allows the overcurrent protection circuit with adjustable overcurrent time to obtain a stable reference voltage under different operating conditions, thereby improving the performance and reliability of the circuit, ensuring that the circuit can accurately judge and handle overcurrent situations, and achieving effective protection for the circuit.

[0024] The current sampling module includes operational amplifier U1-A. The non-inverting input pin 3 of operational amplifier U1-A is connected to the current signal AGND through resistor R49. The node between resistor R49 and the current signal AGND is grounded through capacitor C40. The inverting input pin 2 of operational amplifier U1-A is connected to the current signal CURRENT- through resistor R48. The node between resistor R48 and the current signal CURRENT- is grounded through capacitor C38. A capacitor C37 is connected between the non-inverting input pin 3 and the inverting input pin 2 of operational amplifier U1-A. The positive power supply pin 8 of operational amplifier U1-A is connected to the supply voltage VCC. The negative power supply pin 4 of operational amplifier U1-A is grounded. The output pin 1 of operational amplifier U1-A outputs the voltage signal I_OCP. A capacitor C34 is connected between the positive power supply pin 8 and the output pin 1 of operational amplifier U1-A. A capacitor C35 is connected between the inverting input pin 2 and the output pin 1. A resistor R38 is connected in parallel across capacitor C35.

[0025] The current sampling module accurately samples and processes the current signal. Operational amplifier U1-A plays a crucial role in signal amplification and conversion, transforming the input current signal into a voltage signal I_OCP that can be processed by subsequent circuits. Resistors R49 and R48 are used for voltage division and current limiting of the input current signal to prevent excessive current from damaging the op-amp. Capacitors C40 and C38 act as filters, removing high-frequency noise from the current signal and making the signal input to the op-amp cleaner. Capacitor C37 is connected between the non-inverting and inverting input pins of op-amp U1-A, improving the op-amp's frequency response characteristics and reducing signal distortion. Capacitor C34 is connected between the positive power supply pin 8 and the output pin 1 of op-amp U1-A, helping to stabilize the output voltage and reduce the impact of power supply fluctuations on the output signal. Capacitor C35 and resistor R38 are connected in parallel between the inverting input pin 2 and the output pin 1, forming a negative feedback network that can adjust the op-amp's gain, maintaining a stable linear relationship between the output voltage signal I_OCP and the input current signal. By properly adjusting the parameters of capacitor C35 and resistor R38, precise control of the gain can be achieved to meet the requirements of current sampling accuracy in different application scenarios.

[0026] The above description is illustrative only and not restrictive of this utility model. Those skilled in the art will understand that many modifications, variations or equivalents can be made without departing from the spirit and scope defined by the appended claims, and all such modifications, variations or equivalents will fall within the protection scope of this utility model.

Claims

1. A protection circuit with adjustable overcurrent time, characterized in that: include The current sampling module is used to sample the output current and convert it into a voltage signal I_OCP. The delay circuit module, connected to the current sampling module, includes resistor R83 and capacitor C51. It is used to achieve overcurrent time delay during the charging and discharging process. The charging path consists of resistor R83, diode D20, and capacitor C51, while the discharging path consists of capacitor R71 and diode D24. A reference voltage source is used to provide the reference voltage VREF. The control logic module includes a comparator U1-B. The input of the comparator U1-B is connected to the delay circuit module and the reference voltage source. It is used to compare the delayed voltage signal I_OCP with the reference voltage VREF and output a control signal to turn off the DC-DC converter according to the control signal.

2. The overcurrent protection circuit according to claim 1, wherein: One end of resistor R83 is connected to the voltage signal I_OCP, and the other end is connected to capacitor C51 through diode D20. The other end of capacitor C51 is grounded. One end of resistor R71 is connected to the voltage signal I_OCP, and the other end is connected to the cathode of diode D24. The anode of diode D24 is connected to the inverting input pin 6 of comparator U1-B.

3. The overcurrent protection circuit according to claim 2, wherein: The reference voltage VREF is grounded through resistors R50 and R47 connected in series. The non-inverting input pin 5 of comparator U1-B is connected to the node of resistors R50 and R47.

4. The overcurrent protection circuit according to claim 3, wherein: The non-inverting input pin 5 of comparator U1-B is connected to resistor R39 through diode D12. The other end of resistor R39 is connected to the output pin 7 of comparator U1-B, and the output pin 7 of comparator U1-B is connected to the control signal.

5. The overcurrent protection circuit according to claim 1, wherein: The reference voltage source includes an adjustable regulator U10 for stabilizing the reference voltage. The supply voltage VCC is connected to the positive pin 2 of the adjustable regulator U10 through resistor R44, and the negative pin 3 of the adjustable regulator U10 is grounded. Resistors R45 and R46 are connected in series between the positive and negative pins of the adjustable regulator U10. The reference pin 1 of the adjustable regulator U10 is connected to the node of resistors R45 and R46. Capacitor C45 is connected across the series resistors R45 and R46. One end of capacitor C45 outputs the reference voltage VREF, and the other end is grounded.

6. The overcurrent protection circuit according to claim 1, wherein: The current sampling module includes operational amplifier U1-A. The non-inverting input pin 3 of operational amplifier U1-A is connected to the current signal AGND through resistor R49. The node between resistor R49 and the current signal AGND is grounded through capacitor C40. The inverting input pin 2 of operational amplifier U1-A is connected to the current signal CURRENT- through resistor R48. The node between resistor R48 and the current signal CURRENT- is grounded through capacitor C38. A capacitor C37 is connected between the non-inverting input pin 3 and the inverting input pin 2 of operational amplifier U1-A. The positive power supply pin 8 of operational amplifier U1-A is connected to the supply voltage VCC. The negative power supply pin 4 of operational amplifier U1-A is grounded. The output pin 1 of operational amplifier U1-A outputs the voltage signal I_OCP. A capacitor C34 is connected between the positive power supply pin 8 and the output pin 1 of operational amplifier U1-A. A capacitor C35 is connected between the inverting input pin 2 and the output pin 1. A resistor R38 is connected in parallel across capacitor C35.

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