A load protection circuit with adjustable protection threshold

Abstract

The application discloses a load protection circuit with adjustable protection threshold, comprising a DAC circuit, a comparison circuit, a load acquisition circuit and a MOS tube isolation driving circuit, wherein the DAC circuit and the MOS tube isolation driving circuit are connected with a digital controller, the DAC circuit inputs a protection threshold voltage to the comparison circuit through a constant current and constant voltage circuit, the comparison circuit is connected with the load acquisition circuit and outputs a protection signal to the digital controller. The technical defects of the prior art, such as fixed protection threshold, poor adaptability and the need to redesign the circuit when replacing the load, are solved. The protection threshold is digitally and flexibly adjusted, the digital controller sends a control instruction to the DAC circuit, the protection threshold voltage output by the DAC circuit can be accurately adjusted in real time online, the traditional passive device fixed value design is replaced, the protection threshold adjustment can be completed online without power-off, hardware circuit change and equipment disassembly, different load overcurrent and overload protection requirements can be adapted, and the system normal operation is not interrupted during the adjustment process.

Description

Technical Field

[0001] This invention relates to the field of electronic circuit protection technology, specifically to a load protection circuit with an adjustable protection threshold, applicable to overcurrent and overload protection scenarios for various loads in fields such as industrial control, intelligent devices, and power electronics. Background Technology

[0002] Load protection circuits are commonly used circuit modules in system control. Their core function is to monitor and protect the overcurrent and overload conditions of the load in real time during operation, so as to prevent the load or system from being damaged by abnormal current. This is crucial to the safety and stability of the system.

[0003] Most conventional load protection circuits in China are fixed-threshold designs, where the protection threshold is determined by the parameter settings of passive components such as resistors and capacitors. They can only be designed specifically for the rated operating current and maximum withstand current of a particular load. This type of circuit has two major drawbacks: First, the protection threshold cannot be flexibly adjusted. When the system is replaced with loads of different power and types, the threshold of the original protection circuit becomes incompatible with the operating parameters of the new load, leading to either protection failure and load burnout, or false protection and system malfunction. Second, it has poor adaptability. For different application scenarios and load requirements, the hardware circuit needs to be redesigned and the parameters of passive components adjusted, which not only increases the product development cycle and production costs but also reduces the versatility and reusability of the circuit module. Summary of the Invention

[0004] The purpose of this invention is to address the technical shortcomings of existing load protection circuits, such as fixed protection thresholds, poor adaptability, and the need for circuit redesign when replacing loads, by providing a load protection circuit template with an adjustable protection threshold. This template uses a digital controller in conjunction with a DAC circuit to achieve digital adjustment of the protection threshold voltage. Combined with a load acquisition circuit and a comparison circuit, it completes real-time monitoring and protection. It can adapt to different types and parameters of loads without requiring redesign of the hardware circuit, significantly improving the versatility and flexibility of the load protection circuit.

[0005] The technical solution of this invention: An adjustable protection threshold load protection circuit includes a DAC circuit, a comparator circuit, a load acquisition circuit, and a MOSFET isolation drive circuit. The DAC circuit and the MOSFET isolation drive circuit are both connected to a digital controller. The DAC circuit inputs a protection threshold voltage to the comparator circuit through a constant current and constant voltage circuit. The comparator circuit is connected to the load acquisition circuit and outputs a protection signal to the digital controller.

[0006] The DAC circuit includes a chip U4. The SDI, SCLK, and CS pins of chip U4 are connected to the corresponding pins of the digital controller, the VDD pin is connected to a 3.3V digital power supply, the AGND and DGND are connected to analog ground and digital ground, respectively, the VREF pin is connected to a 2.5V reference voltage, and the VOUT pin outputs an analog signal to the input of operational amplifier U6.2. The inverting input of operational amplifier U6.2 is shorted to its output and connected to a comparator circuit.

[0007] The chip U4 is a DA8830ICDR analog-to-digital converter.

[0008] The comparator circuit includes operational amplifiers U7.2 and U8.2. The non-inverting input of operational amplifier U7.2 is connected to the output of operational amplifier U6.2. The output of operational amplifier U7.2 is connected to the inverting input of operational amplifier U8.2 and resistor R6 through resistor R5. The output of operational amplifier U8.2 and resistor R6 are connected to the non-inverting input IN+ of comparator U1. The non-inverting input of operational amplifier U8.2 is connected to the sampling circuit and grounded through resistor R1. The output of comparator U1 outputs the I_SHOUT signal to the digital controller. The power supply pin VDD is connected to a 3.3V power supply and is connected to resistor R3. Resistor R3 is connected to the inverting input IN- of comparator U1 and resistor R4. Resistor R4 is grounded.

[0009] U1 is a GS8743-TR comparator.

[0010] The sampling circuit includes a sampling chip U10. The positive terminal of the input of the sampling chip U10 is connected to the source of the MOS transistor Q1, and the negative terminal of the input is grounded. The VIOUT pin is connected to the positive input of the operational amplifier U8.2 through a resistor R2. The VCC pin is connected to a +5V power supply and grounded through a capacitor C4. The FILTER pin is grounded through a capacitor and its GND pin.

[0011] The chip U10 is an ACS712ELCTR-20A-T current sensor.

[0012] The MOS transistor isolation drive circuit includes a diode Q2 and an optocoupler U9. The base of diode Q2 is connected to the P_CTRL signal of the digital controller, and the collector is connected to a 3V3 power supply. The emitter is connected to the positive input terminal of optocoupler U9, the negative input terminal is grounded, the positive output terminal is connected to a 12V power supply through resistor R7, and the negative output terminal is connected to the gate of MOS transistor Q1. The drain of MOS transistor Q1 is connected to the load power supply, and the drain is connected to the load.

[0013] The digital controller is an STM32 series microcontroller.

[0014] The beneficial effects of this invention are: The protection threshold can be flexibly adjusted digitally, supporting online real-time adjustment: By sending control commands to the DAC circuit through the digital controller, the protection threshold voltage output of the DAC circuit can be adjusted online in real time and with precision. This replaces the traditional passive component setting design. The protection threshold can be adjusted online without power interruption, hardware circuit modification, or equipment disassembly. It can adapt to different overcurrent and overload protection requirements of different loads, and the adjustment process does not interrupt the normal operation of the system.

[0015] High versatility and adaptability to various loads: This circuit template is a universal design that can be applied to different types of loads such as resistive, inductive, and capacitive loads, as well as load scenarios with different power and rated current. It supports online one-click switching of protection thresholds, solving the problem of "one type of protection circuit for one type of load" in traditional circuits, and greatly reducing the design and adaptation costs of the circuit.

[0016] High real-time monitoring and protection: The ACS712ELCTR-20A-T current sensor is used to achieve real-time sampling of the load current. Combined with the GS8743-TR high-speed comparator, the sampled signal is quickly compared with the threshold signal. Once an abnormal load is detected, a protection signal can be immediately output to the digital controller. The protection response is fast and effectively avoids damage to the load and system.

[0017] Good circuit isolation and strong anti-interference capability: The optocoupler U9 realizes electrical isolation between the digital controller and the MOSFET drive circuit, avoiding high voltage and high current interference on the load side to the digital control side signal, and improving the working stability of the circuit in complex industrial environments.

[0018] The hardware structure is modular and easy to integrate: each module has independent functions and clear interfaces. The online threshold adjustment function can be directly embedded into the existing digital control system. It supports multiple online adjustment methods such as host computer, local buttons, and touch screen, which facilitates maintenance and upgrades. Attached Figure Description

[0019] Figure 1 This is a schematic diagram illustrating the principle of the present invention; Figure 2 This is a schematic diagram of the circuit structure of the present invention. Detailed Implementation

[0020] The load protection circuit template of this invention is based on an STM32 series digital controller and consists of four core components: protection threshold setting, load current sampling, signal comparison and judgment, MOSFET driving, and protection execution. The overall working logic is as follows: the digital controller outputs an adjustable protection threshold voltage through a DAC circuit; the load acquisition circuit collects the load's operating current in real time and converts it into a corresponding voltage signal; the comparison circuit compares the sampled voltage signal with the threshold voltage signal; when the sampled voltage signal exceeds the threshold voltage signal, the comparison circuit outputs a protection signal to the digital controller; the digital controller performs protection actions such as turning off the MOSFET according to the protection signal, cutting off the load power supply and realizing overcurrent and overload protection for the load; when the load returns to normal, the digital controller can re-drive the MOSFET to conduct and restore the load power supply.

[0021] The specific working principles of each stage are as follows: Protection threshold setting stage: The digital controller sends digital control signals to the DAC chip U4 (DA8830ICDR) through the SDI, SCLK, and CS pins. The DAC chip converts the digital signals into corresponding analog voltage signals. After signal buffering and constant current and constant voltage processing by the voltage follower composed of operational amplifier U6.2, the signals are input to the comparator circuit. This analog voltage signal is the threshold voltage for load protection. The digital controller can precisely change the magnitude of the threshold voltage by adjusting the output digital signal.

[0022] Load current sampling stage: The ACS712ELCTR-20A-T current sensor U10 is used to collect the source current of MOSFET Q1 (i.e., the working current of the load) in real time. The sensor converts the collected current signal into a 0-5V voltage signal, outputs it through the VIOUT pin, and transmits it to the positive input of the operational amplifier U8.2 of the comparator circuit through resistor R2, thus completing the electrical signal conversion and transmission of the load current.

[0023] Signal comparison and judgment stage: After buffering the threshold voltage signal, operational amplifier U7.2 inputs it to the inverting input of operational amplifier U8.2 via resistor R5. Operational amplifier U8.2 differentially amplifies the sampled voltage signal at the positive input and the threshold voltage signal at the inverting input. The processed signal is input to the positive input IN+ of comparator U1 (GS8743-TR). The inverting input IN- of comparator U1 is provided with a reference voltage by a voltage divider circuit composed of resistors R3 and R4. When the sampled voltage signal is greater than the threshold voltage signal, comparator U1 outputs a high-level I_SHOUT protection signal to the digital controller to realize the judgment and output of abnormal signals.

[0024] MOSFET drive and protection execution: The P_CTRL drive signal output by the digital controller is amplified by transistor Q2 and drives optocoupler U9 to conduct. Optocoupler U9 transmits the 12V power signal to the gate of MOSFET Q1, turning on MOSFET Q1 and allowing the load power supply to power the load, thus achieving normal load drive. Optocoupler U9 achieves electrical isolation between the digital control side and the power drive side, improving anti-interference capability. When the digital controller receives the I_SHOUT protection signal, it immediately pulls down the P_CTRL signal, turning off transistor Q2 and optocoupler U9. The gate of MOSFET Q1 loses its drive voltage and turns off, cutting off the load power supply and completing overload protection.

[0025] The core advantage of this invention is that the protection threshold can be flexibly adjusted. The following provides specific threshold adjustment and protection embodiments for the three most common types of loads in industrial scenarios: resistive loads, inductive loads, and capacitive loads, combined with load parameters of different rated currents. In each embodiment, the STM32F103 series microcontroller is used as the digital controller, and the circuit hardware structure remains unchanged. Only the output threshold voltage of the DAC circuit is adjusted through the digital controller program.

[0026] Example 1: Threshold adjustment protection for resistive loads The operating current of resistive loads (such as resistance heaters and resistance furnaces) is stable with no starting surge current, and the protection threshold can be set to 1.2 times the rated current (i.e., 6A).

[0027] Threshold voltage calculation: The output sensitivity of the ACS712ELCTR-20A-T current sensor is 100mV / A. The sampling voltage corresponding to the 5A rated current is 0.5V, and the sampling voltage corresponding to the 6A protection current is 0.6V. Therefore, the output threshold voltage of the DAC circuit is adjusted to 0.6V.

[0028] Threshold setting operation: The STM32 microcontroller sends a digital control command to the DA8830ICDR to control its output of a 0.6V analog threshold voltage, which is then buffered by operational amplifiers U6.2 and U7.2 and input to the comparator circuit.

[0029] For threshold adjustment, communication via RS485 / CAN / Ethernet is available. The host computer sends threshold adjustment commands to the STM32 microcontroller, which analyzes and updates the DAC output voltage in real time, enabling remote online threshold adjustment. Alternatively, the device's local touchscreen provides a numerical input interface, allowing manual input of the target protection current. The microcontroller automatically calculates and updates the threshold voltage online without requiring power interruption. Keypad step adjustment is also available: the panel features "+ / -" buttons; each press increases / decreases the protection threshold by 0.1A. The microcontroller adjusts the DAC output in real time, and the threshold changes immediately.

[0030] Protection execution process: When the operating current of the resistance heating load exceeds 6A due to short circuit, aging, or other reasons, the sampling voltage collected by the current sensor exceeds 0.6V. The comparator U1 outputs the I_SHOUT high-level signal to the microcontroller, and the microcontroller immediately pulls the P_CTRL signal low, turns off the optocoupler U9 and MOSFET Q1, and cuts off the power supply to the load. After the fault is cleared, the microcontroller outputs the P_CTRL high-level signal again to restore the power supply to the load.

[0031] Example 2: Threshold adjustment protection for inductive loads Inductive loads (such as DC motors and solenoid valves) have inrush currents during startup (usually 3-5 times the rated current). If the threshold is set directly according to the rated current, false protection will occur. Therefore, dual threshold protection is required, namely a high threshold during startup and a low threshold during normal operation.

[0032] Threshold voltage calculation: The output sensitivity of ACS712ELCTR-20A-T is 100mV / A. The protection threshold for normal motor operation is set to 1.5 times the rated current (4.5A, corresponding to a sampling voltage of 0.45V), and the protection threshold for the start-up phase is set to 5 times the rated current (15A, corresponding to a sampling voltage of 1.5V).

[0033] Threshold setting operation: The program is written using an STM32 microcontroller to send an instruction to the DA8830ICDR during the motor start-up phase (first 2 seconds) to output a high threshold voltage of 1.5V. After the start-up is complete, the microcontroller automatically switches the instruction to adjust the DAC output threshold voltage to a low threshold voltage of 0.45V. The microcontroller has built-in timing logic that automatically outputs a high threshold during the start-up phase and switches to a low threshold online after the start-up is complete, without any manual intervention.

[0034] Protection execution process: When the motor starts, the surge current is about 9A, which does not exceed the high threshold of 15A, so the circuit does not trigger the protection. After the start-up is completed, the motor operating current stabilizes at about 3A. If the current exceeds 4.5A due to jamming, stalling, or other reasons, and the sampling voltage exceeds 0.45V, the comparator U1 outputs a protection signal, the microcontroller shuts down the MOSFET Q1, cuts off the power supply to the motor, and realizes overload protection.

[0035] Example 3: Threshold adjustment protection for capacitive loads Capacitive loads (such as capacitor compensation cabinets and capacitor filter modules) have charging surge currents that last for a very short time (milliseconds). The protection threshold should be set to 4 times the rated current, and a delay protection should be added to prevent the surge current from triggering false protection.

[0036] Threshold voltage calculation: The output sensitivity of ACS712ELCTR-20A-T is 100mV / A, and the protection threshold for capacitive load is set to 4 times the rated current (8A, corresponding to a sampling voltage of 0.8V).

[0037] Threshold setting and delay configuration: The STM32 microcontroller sends a command to the DA8830ICDR to output a threshold voltage of 0.8V; at the same time, a 50ms delay judgment program is set in the microcontroller, and the protection action is only executed when the comparator U1 continuously outputs the I_SHOUT protection signal for more than 50ms.

[0038] Protection execution process: When the capacitor load is charging, the instantaneous surge current is about 7A, which does not exceed the protection threshold of 8A and the duration is less than 50ms, so the circuit does not trigger the protection. After charging is completed, the load operating current stabilizes at about 2A. If the current continues to exceed 8A for more than 50ms due to capacitor breakdown, short circuit, or other reasons, the microcontroller will receive a continuous protection signal, turn off the MOSFET Q1, cut off the power supply to the load, and realize overcurrent protection.

Claims

1. A load protection circuit with an adjustable protection threshold, characterized in that: It includes a DAC circuit, a comparator circuit, a load acquisition circuit, and a MOSFET isolation drive circuit. The DAC circuit and the MOSFET isolation drive circuit are both connected to the digital controller. The DAC circuit inputs a protection threshold voltage to the comparator circuit through a constant current and constant voltage circuit. The comparator circuit is connected to the load acquisition circuit and outputs a protection signal to the digital controller.

2. The load protection circuit with adjustable protection threshold according to claim 1, characterized in that: The DAC circuit includes a chip U4. The SDI, SCLK, and CS pins of chip U4 are connected to the corresponding pins of the digital controller, the VDD pin is connected to a 3.3V digital power supply, the AGND and DGND are connected to analog ground and digital ground, respectively, the VREF pin is connected to a 2.5V reference voltage, and the VOUT pin outputs an analog signal to the input of operational amplifier U6.

2. The inverting input of operational amplifier U6.2 is shorted to its output and connected to a comparator circuit.

3. The load protection circuit with adjustable protection threshold according to claim 2, characterized in that: The chip U4 is a DA8830ICDR analog-to-digital converter.

4. The load protection circuit with adjustable protection threshold according to claim 1, characterized in that: The comparator circuit includes operational amplifiers U7.2 and U8.

2. The non-inverting input of operational amplifier U7.2 is connected to the output of operational amplifier U6.

2. The output of operational amplifier U7.2 is connected to the inverting input of operational amplifier U8.2 and resistor R6 through resistor R5. The output of operational amplifier U8.2 and resistor R6 are connected to the non-inverting input IN+ of comparator U1. The non-inverting input of operational amplifier U8.2 is connected to the sampling circuit and grounded through resistor R1. The output of comparator U1 outputs the I_SHOUT signal to the digital controller. The power supply pin VDD is connected to a 3.3V power supply and is connected to resistor R3. Resistor R3 is connected to the inverting input IN- of comparator U1 and resistor R4. Resistor R4 is grounded.

5. The load protection circuit with adjustable protection threshold according to claim 4, characterized in that: U1 is a GS8743-TR comparator.

6. The load protection circuit with adjustable protection threshold according to claim 1, characterized in that: The sampling circuit includes a sampling chip U10. The positive terminal of the input of the sampling chip U10 is connected to the source of the MOS transistor Q1, and the negative terminal of the input is grounded. The VIOUT pin is connected to the positive input of the operational amplifier U8.2 through a resistor R2. The VCC pin is connected to a +5V power supply and grounded through a capacitor C4. The FILTER pin is grounded through a capacitor and its GND pin.

7. The load protection circuit with adjustable protection threshold according to claim 6, characterized in that: The chip U10 is an ACS712ELCTR-20A-T current sensor.

8. The load protection circuit with adjustable protection threshold according to claim 1, characterized in that: The MOS transistor isolation drive circuit includes a diode Q2 and an optocoupler U9. The base of diode Q2 is connected to the P_CTRL signal of the digital controller, and the collector is connected to a 3V3 power supply. The emitter is connected to the positive input terminal of optocoupler U9, the negative input terminal is grounded, the positive output terminal is connected to a 12V power supply through resistor R7, and the negative output terminal is connected to the gate of MOS transistor Q1. The drain of MOS transistor Q1 is connected to the load power supply, and the drain is connected to the load.

9. The load protection circuit with adjustable protection threshold according to claim 1, characterized in that: The digital controller is an STM32 series microcontroller.

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