Special protection device for over-current and short circuit of H-bridge circuit

Abstract

The invention discloses a special protection device for over-current and short circuit of an H-bridge circuit. The special protection device comprises a sampling resistor R20 used for detecting over-current and short circuit of the H-bridge circuit of a direct current motor control system, a driving ICU3 used for controlling on-off of the H-bridge circuit, and a current monitoring and protection unit, the output control end of the driver ICU3 is connected with the input control end of the H-bridge circuit, the enabling end of the driver ICU3 is connected with the control signal output end of the current monitoring and protection unit, and the control signal input end of the current monitoring and protection unit is connected with the sampling resistor. The protection circuit composed of the integrated operational amplifier and the comparator is used, when the direct current motor control system is short-circuited or over-current, the H-bridge circuit can be closed within several microseconds, and therefore it is guaranteed that circuit board elements of the direct current motor control system and the direct current motor are not damaged. And short-circuit signals collected by the sampling resistor are accessed to a microcontroller of a direct-current motor control system, and the signals are latched, so that logic control and operation are facilitated.

Description

Technical Field

[0001] The invention relates to an H-bridge circuit driving circuit, in particular to a special protection device for overcurrent and short circuit of the H-bridge circuit. Background Art

[0002] At present, most DC motor control systems use H-bridge circuits to achieve forward and reverse operation of DC motors. During the operation of DC motors, when external machinery or DC motors fail (such as stalling, short circuit), the H-bridge circuit is easily burned out. To solve the above problems, the conventional method is to add a fusible or self-recovering fuse at the power supply end to prevent the H-bridge circuit or DC motor from burning out. Although the use of fusible fuses can prevent the subsequent circuit components or DC motors from burning out, the fusible fuses need to be replaced manually on site after they are blown. The self-recovering fuse is a temperature-sensitive device that needs to be overheated to play a protective role, which delays the protection time and easily causes the protected circuit to burn out; in addition, because the self-recovering fuse is related to temperature, when the operating temperature changes, its protection current changes accordingly, and the change is still large, which can easily cause improper protection.

[0003] Chinese invention patent CN203553904U discloses an overcurrent and short-circuit protection circuit for a servo motor. The current sampling signal is directly input into a single-chip microcomputer through a current sampling resistor to determine whether the H-bridge is short-circuited / overcurrent. Since the single-chip microcomputer sampling requires an interval time, the fastest cut-off takes tens of milliseconds, and the hardware protection operation cannot be performed in a short time.

[0004] Chinese invention patent CN211880321U discloses a controllable logic circuit and an H-bridge circuit for an H-bridge circuit. This solution solves the problem of preventing the upper and lower bridge arms of the H-bridge circuit from being opened at the same time and causing a short circuit, but does not solve the problem of the H-bridge circuit burning out due to external mechanical or motor failures (such as stalling, short circuit). Summary of the invention

[0005] In view of this, the present invention proposes a special protection device for overcurrent and short circuit of an H-bridge circuit, which can quickly shut down the H-bridge circuit when a short circuit or overcurrent occurs in the H-bridge circuit.

[0006] To achieve the above object, the present invention adopts the following technical solutions: The H-bridge circuit overcurrent and short-circuit special protection device of the present invention includes a sampling resistor R20 for detecting overcurrent and short circuit of the H-bridge circuit of the DC motor control system, a driver ICU3 for controlling the on and off of the H-bridge circuit, and a current monitoring and protection unit; the output control terminal of the driver ICU3 is connected to the input control terminal of the H-bridge circuit, the enable terminal of the driver ICU3 is connected to the control signal output terminal of the current monitoring and protection unit, and the control signal input terminal of the current monitoring and protection unit is connected to the sampling resistor.

[0007] Optionally, the current monitoring and protection unit includes an integrated operational amplifier U1 and a comparator U2; the non-inverting input terminal of the integrated operational amplifier U1 is connected to the sampling resistor R20 via a low-pass filter composed of R2 and C1, and the inverting input terminal of the integrated operational amplifier U1 is connected to the output terminal of the integrated operational amplifier U1 via a high-pass filter composed of R3 and C2. The relationship between the voltage at the output terminal of U1 and the input signal at its non-inverting input terminal is: , by selecting the appropriate resistance size, the current amplification factor can be adjusted.

[0008] The output end of the integrated operational amplifier U1 is connected to the in-phase input end of the comparator U2 through R4, and the inverting input end of the comparator U2 is connected to the working power supply VCC through a voltage divider circuit composed of resistors R5 and R6. By adjusting the two resistors R5 and R6, the current size when the comparator U2 outputs a high level can be changed. The output end of the comparator U2 is connected to the enable end of the driver ICU3.

[0009] Furthermore, the signal input end of the driving ICU3 is respectively connected to the logic signal output end of the microcontroller of the DC motor control system; the short-circuit signal collected by the sampling resistor R20 of the current monitoring and protection unit is connected to the external interrupt signal input end of the microcontroller of the DC motor control system.

[0010] The present invention uses a protection circuit composed of an integrated operational amplifier and a comparator. When a short circuit or overcurrent occurs in the DC motor control system, the H-bridge circuit can be turned off within a few microseconds, thereby ensuring that the circuit board components and the DC motor of the DC motor control system are not damaged. In addition, the short-circuit signal collected by the sampling resistor is connected to the microcontroller of the DC motor control system, and the signal is latched to facilitate logical control and operation. At the same time, the present invention has a modular design and can be used to protect other high-power switching devices. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] Figure 1 It is a circuit schematic diagram of the present invention.

[0012] Figure 2 It is the principle diagram of the H-bridge circuit described in the present invention.

[0013] Figure 3 The invention discloses a circuit principle block diagram of a DC motor control system. DETAILED DESCRIPTION

[0014] The following is a detailed description of an embodiment of the present invention in conjunction with the accompanying drawings. This embodiment is implemented on the premise of the technical solution of the present invention, and a detailed implementation method and a specific operation process are given, but the protection scope of the present invention is not limited to the following embodiment.

[0015] It should be noted that in the description of the present invention, unless otherwise clearly specified and limited, the terms "connected" and "connection" that may appear should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be an indirect connection through an intermediate medium, and the internal communication of two components. For those skilled in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0016] like Figure 1-3 As shown, the H-bridge circuit overcurrent and short-circuit special protection device of the present invention includes a sampling resistor R20 for detecting overcurrent and short circuit of the H-bridge circuit of the DC motor control system, a driver ICU3 for controlling the on and off of the H-bridge circuit, and a current monitoring and protection unit; the output control end of the driver ICU3 is connected to the input control end of the H-bridge circuit, the enable end of the driver ICU3 is connected to the control signal output end of the current monitoring and protection unit, the control signal input end of the current monitoring and protection unit is connected to the high potential end of the sampling resistor R20, and the low potential end of the sampling resistor R20 is grounded.

[0017] The DC motor control system of this embodiment is as follows Figure 3 As shown, the power supply voltage stabilization circuit provides a stable voltage for the entire system, and the drive circuit provides a stable voltage and sufficient current for the operation of the DC motor. The microcontroller communicates with other devices through an external communication interface, obtains instructions, and other operations. In order to control the speed of the DC motor, the PWM interface of the microcontroller is required; if the speed does not need to be controlled, and only the forward and reverse and start-stop functions need to be realized, the PWM output port can be replaced with a normal IO port. The driver ICU3 has an enable terminal, and the enable terminal is connected to the microcontroller IO port. The H-bridge circuit is implemented using four standard NMOS tubes / IGBTs, and the specific model needs to be selected according to the rated power of the DC motor. The current sampling resistor R20 is connected between the common low end and the ground of the H-bridge circuit, and this resistor can collect the current flowing through the MOS tube. The DC motor is connected through interfaces M1 and M2 in the middle of the H-bridge circuit, and the DC motor model is specifically selected according to the usage scenario. In this embodiment, the current sampling resistor R20 is connected to the current monitoring and protection unit. When the current exceeds the set value, the enable end of the driver ICU3 will be instantly turned off, and the signal will be sent to the interrupt port of the microcontroller. In addition, the voltage signal of the current sampling resistor R20 is amplified and connected to the pin of the microcontroller with AD (analog-to-digital conversion) function.

[0018] like Figure 2As shown, Q1, Q2, Q3, and Q4 in the H-bridge circuit of this embodiment are power-type switching devices such as MOS or IGBT that match the rated power of the DC motor; this embodiment takes an N-channel MOS tube as an example, where Q1 and Q3 serve as the high side of the H-bridge circuit, and Q2 and Q4 serve as the low side of the H-bridge circuit. The control signals H1, H2, L1, and L2 come from the driver IC U3, and respectively control the four MOS tubes of the H-bridge circuit, and can control them to be turned on and off. One end of the resistors R13, R14, R15, and R16 are respectively connected to the control electrodes of the four MOS tubes Q1, Q2, Q3, and Q4, and the other end is connected to the ground terminal GND, as a pull-down resistor of the control electrode, to prevent the MOS tube from malfunctioning when the output end of the driver IC U3 is in a high-impedance state. One end of the current sampling resistor R20 is connected to the output end of the low-side MOS tube, and the other end is connected to the ground terminal GND. The current sampling resistor R20 is usually selected to be a high-power milliohm level, so that the voltage on the DC motors M1 and M2 hardly changes when the current changes.

[0019] The current sampling resistor R20 can convert the large current signal flowing through the DC motor into a voltage signal, which is led out by the network CURRENT_S for amplification / collection. Interfaces M1 and M2 are connected to the two ends of the DC motor to realize the forward and reverse rotation of the DC motor; at the same time, if the control signal added to the control electrode of the four MOS tubes Q1, Q2, Q3, and Q4 is PWM or other periodically changing signals, the speed of the DC motor can be changed.

[0020] like Figure 3 As shown, PWM1, PWM2, PWM3, and PWM4 in the driver ICU3 are logic signal interfaces output by the microcontroller; the SHUT_OFF signal comes from the output end of the comparator U2, and this signal is connected to the enable end of the driver ICU3. Depending on the model and function of the driver ICU3, the enable end may be high level effective or low level effective. This embodiment takes low level effective as an example. Resistors R9, R10, R11, and R12 are respectively connected to the output end of the driver ICU3, and the other ends of the resistors R9, R10, R11, and R12 are respectively connected to H1, H2, L1, and L2, that is, the control ends of the four MOS tubes Q1, Q2, Q3, and Q4 in the H-bridge circuit, which are used to adjust the gate currents of the four MOS tubes Q1, Q2, Q3, and Q4, thereby adjusting the switching speeds of the four MOS tubes Q1, Q2, Q3, and Q4, and thus optimizing electromagnetic radiation. According to the function of driver ICU3, the levels of H1, H2, L1 and L2 are controlled by the logic signal at the input end. At the same time, when the enable end of driver ICU3 is disabled, the output end of driver IC U3 is in high impedance state. At this time, the four MOS tubes Q1, Q2, Q3 and Q4 in the H-bridge circuit are all in the off state.

[0021] like Figure 3As shown, the signal CURRENT_S comes from the current sampling resistor R20 in the H-bridge circuit module, that is, the voltage signal of the DC motor current on this resistor, which is usually only in the millivolt level. This signal is connected to the non-inverting input terminal of the precision integrated operational amplifier U1 after passing through the low-pass filter composed of resistor R2 and capacitor C1. One end of the resistor R1 is grounded, and the other end is connected to the inverting input terminal of the precision integrated operational amplifier U1, and is also connected to one end of the resistor R3 and capacitor C2; the other end of the high-pass filter composed of resistor R3 and capacitor C2 is connected to the output terminal of the precision integrated operational amplifier U1, forming a standard amplification circuit. The relationship between the output voltage of the precision integrated operational amplifier U1 and the input signal is: ; The current amplification factor can be adjusted by selecting a suitable resistance value; the output signal VO_U1 of the precision integrated operational amplifier U1 is connected to the pin with ADC acquisition function of the microcontroller, and the real-time acquisition of the DC motor current is achieved through the AD conversion inside the microcontroller.

[0022] The output end of the precision integrated operational amplifier U1 is connected to the non-inverting input end of the comparator U2 through the resistor R4. The working power supply VCC is divided by the resistors R5 and R6 and connected to the inverting input end of the comparator U2 through the filter capacitor C3. The current value when the comparator U2 outputs a high level can be changed by adjusting the two resistors R5 and R6. The output end of the comparator U2 outputs the SHUT_OFF signal through the current limiting resistor R7 and is directly input to the enable end of the driver ICU3. At the same time, the signal is connected to the external interrupt input pin of the microcontroller. The effect of this connection method: When the DC motor or the external interface of M1 and M2 is short-circuited or overcurrent occurs, the current flowing through the current sampling resistor R20 will increase instantly, causing the output voltage of the CURRENT_S signal after being amplified by the precision integrated operational amplifier U1 to be too high, exceeding the threshold value set at the inverting input of the comparator U2, thereby changing the output of the comparator U2 from the original low level to the high level; the SHUT_OFF signal connects the driver ICU3 enable terminal and the microcontroller external interrupt pin, driving the ICU3 output terminal to enter the high impedance state instantly, causing the H-bridge circuit to be instantly shut down. At this time, the current flowing through the four MOS tubes Q1, Q2, Q3, and Q4 of the H-bridge circuit is cut off, and the current flowing through the sampling resistor R20 becomes 0 again, and the SHUT_OFF signal will become low again. In order to prevent the SHUT_OFF signal from oscillating, the SHUT_OFF signal needs to be latched. There is no unique method, and it can be entered into a latch or connected to other ICs. In this embodiment, the SHUT_OFF signal is connected to the external interrupt pin of the microcontroller. When the SHUT_OFF signal level changes, the microcontroller will immediately enter the external interrupt program. In the interrupt program, the microcontroller will immediately make the four front-stage control signals of the H-bridge circuit, namely PWM1, PWM2, PWM3, and PWM4, output low levels, and turn off the four N-channel MOS tubes Q1, Q2, Q3, and Q4; therefore, when a short circuit or overcurrent occurs, the four MOS tubes Q1, Q2, Q3, and Q4 can be turned off within a few microseconds, thereby achieving the purpose of protecting the circuit board components and the DC motor.

[0023] The above solution uses low-end current sampling (the current sampling resistor is at the bottom of the H-bridge). Similarly, the current sampling resistor can be placed at the top of the H-bridge and a dedicated current acquisition chip can be used to amplify the current to achieve the same function.

[0024] Finally, it should be emphasized that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions recorded in the aforementioned embodiments without creative work, or replace some of the technical features therein with equivalents. Therefore, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A special protection device for overcurrent and short circuit of H-bridge circuit, characterized in that: It includes a sampling resistor for detecting overcurrent and short circuit of the H-bridge circuit of the DC motor control system, a driver ICU3 for controlling the on and off of the H-bridge circuit, and a current monitoring and protection unit; the output control terminal of the driver ICU3 is connected to the input control terminal of the H-bridge circuit, the enable terminal of the driver ICU3 is connected to the control signal output terminal of the current monitoring and protection unit, and the control signal input terminal of the current monitoring and protection unit is connected to the sampling resistor.

2. The H-bridge circuit overcurrent and short-circuit protection device according to claim 1, characterized in that: The current monitoring and protection unit includes an integrated operational amplifier U1 and a comparator U2; the non-inverting input terminal of the integrated operational amplifier U1 is connected to the sampling resistor through a low-pass filter, and the inverting input terminal of the integrated operational amplifier U1 is connected to the output terminal of the integrated operational amplifier U1 through a high-pass filter; the output terminal of the integrated operational amplifier U1 is connected to the non-inverting input terminal of the comparator U2, the inverting input terminal of the comparator U2 is connected to the working power supply through a voltage divider circuit, and the output terminal of the comparator U2 is connected to the enable terminal of the driver ICU3.

3. The H-bridge circuit overcurrent and short-circuit protection device according to claim 1 or 2, characterized in that: The signal input end of the driving ICU3 is respectively connected to the logic signal output end of the microcontroller of the DC motor control system; the short-circuit signal collected by the sampling resistor of the current monitoring and protection unit is connected to the external interrupt signal input end of the microcontroller of the DC motor control system.

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