Load driving circuit with fast protection function and protection method thereof

Abstract

The application discloses a load driving circuit with a quick protection function, which comprises a control circuit and a switch tube; a first output end and a second output end of the load driving circuit are used for connecting two ends of a load respectively, one of the output ends is connected with a conducting end of the switch tube as a moving point, and the other output end is used for connecting a power supply or the ground; an input end of the control circuit is connected with the conducting end of the switch tube as the moving point, an output end of the control circuit is connected with a control end of the switch tube, the control circuit is used for judging whether the output of the load driving circuit is abnormal according to a voltage signal of the moving point and a PWM signal output by the control circuit to the switch tube, and the switch tube is closed when the output of the load driving circuit is abnormal. The application further discloses a quick protection method of the load driving circuit. The application can quickly detect abnormal conditions of short circuit or open circuit of the output end of the load driving circuit and make a response.

Description

TECHNICAL FIELD

[0001] The present application relates to the protection technology of load driving circuit. BACKGROUND

[0002] Inductive load and related driving circuit are widely used. Many actuators such as electromagnetic valve, motor and so on are inductive load, and the inductive load is generally driven by PWM mode, and the driving circuit is mainly composed of power semiconductor devices. In order to improve the driving efficiency and optimize the heat dissipation design, the semiconductor devices are required to have low on-resistance and fast turn-on and turn-off capability. When the abnormality occurs at the output end of the driving circuit (such as short circuit), the abnormal large current exceeding the specifications of the semiconductor devices or the specifications of the inductive load will occur, thereby causing abnormal large power loss. In order to protect the driving circuit and the load, the driving circuit is required to have the circuit design for corresponding protection against the possible abnormality at the output end. The difficulty of protection lies in the response time. For the semiconductor switch such as MOS tube, when the voltage is constant, the safe working range and the protection response time of the same MOS tube are closely related to the size of the current flowing through the MOS tube: 1) when the size of the current flowing through the MOS tube is constant, the longest protection response time allowed is constant. Within the longest protection response time range, the duration of large power loss is short, and the MOS tube works within the safe working range, and if the longest protection response time range is exceeded, the duration of large power loss is long, and the MOS tube exceeds the safe working range; 2) the larger the current flowing through the MOS tube, the shorter the protection response time required. SUMMARY

[0003] The technical problem to be solved by the present application is to provide a load driving circuit with fast protection function, which can quickly detect the abnormality of short circuit or open circuit at the output end of the load driving circuit and make a response.

[0004] Another technical problem to be solved by the present application is to provide a fast protection method of load driving circuit.

[0005] According to one aspect of the present application, a load driving circuit with fast protection function is provided, comprising a control circuit, a switch tube, a first output terminal and a second output terminal; the switch tube is connected in series in a power supply circuit in which a power supply supplies power to a load, and has a control terminal, a first conduction terminal and a second conduction terminal; an output terminal of the control circuit is connected to the control terminal of the switch tube to output a PWM signal to the switch tube, so as to control the conduction and turn-off of the switch tube; the first output terminal and the second output terminal of the load driving circuit are used to connect two ends of the load respectively, and one of the output terminals is connected to the conduction terminal of the switch tube as a moving point, and the other output terminal is used to connect a power supply or ground; wherein, the input terminal of the control circuit is connected to the conduction terminal of the switch tube as the moving point, and the control circuit is used to judge whether the output of the load driving circuit is abnormal according to the voltage signal of the moving point and the PWM signal output by the control circuit to the switch tube, and to turn off the switch tube when the output of the load driving circuit is abnormal.

[0006] According to another aspect of the present application, a fast protection method of a load driving circuit is also provided, the load driving circuit comprising a control circuit, a switch tube, a first output terminal and a second output terminal; the switch tube has a control terminal, a first conduction terminal and a second conduction terminal; an output terminal of the control circuit is connected to the control terminal of the switch tube; the first output terminal and the second output terminal of the load driving circuit are used to connect two ends of the load respectively, and one of the output terminals is connected to the conduction terminal of the switch tube as a moving point, and the other output terminal is connected to a power supply or ground; the fast protection method of the load driving circuit comprises the following steps: judging whether the output of the load driving circuit is abnormal according to the voltage signal of the moving point and the PWM signal output by the control circuit to the switch tube, and turning off the switch tube when the output of the load driving circuit is abnormal.

[0007] The present application has at least the following technical effects:

[0008] The embodiment of the present application utilizes the different corresponding relationship between the driving signal of the switch tube and the voltage of the moving point of the switch tube in the normal working mode and in the case that the output of the load driving circuit is abnormal, directly compares the driving signal of the switch tube and the voltage of the moving point of the switch tube, so as to quickly detect the abnormal condition that the output of the load driving circuit is short-circuited or disconnected, and turn off the switch tube, thereby providing reliable protection for the load short-circuit, the output terminal short-circuit of the load driving circuit to the power supply, and the output terminal short-circuit of the load driving circuit to the ground, improving the safety and reliability of the load driving circuit, and enabling the load driving circuit to use a switch tube semiconductor device with a smaller safe working range, thereby achieving the effect of reducing cost. BRIEF DESCRIPTION OF DRAWINGS

[0009] In order to make the technical solutions in the embodiments of the present application clearer, the accompanying drawings needed in the embodiments will be briefly introduced. Obviously, the accompanying drawings in the following description only show some embodiments of the present application, and for those skilled in the art, other drawings can be obtained without any creative effort based on these drawings.

[0010] Figure 1 A circuit schematic diagram of the load driving circuit with the fast protection function according to the first embodiment of the present application is shown.

[0011] Figure 2 A circuit schematic diagram of the current limiting circuit according to the first embodiment of the present application is shown.

[0012] Figure 3 A circuit schematic diagram of the load driving circuit with the fast protection function according to the second embodiment of the present application is shown.

[0013] Figure 4 A circuit schematic diagram of the load driving circuit with the fast protection function according to the third embodiment of the present application is shown.

[0014] Figure 5 A circuit schematic diagram of the load driving circuit with the fast protection function according to the fourth embodiment of the present application is shown.

[0015] Figure 6 A circuit schematic diagram of the load driving circuit with the fast protection function according to the fifth embodiment of the present application is shown. DETAILED DESCRIPTION

[0016] For an active semiconductor device such as a MOS tube (MOSFET), the size of the gate-source voltage V GS of the MOS tube can control the turn-on or turn-off of the drain D and the source S of the MOS tube. According to the MOS tube driving signal V C related to the size of the V GS of the MOS tube, the drain-source of the MOS tube has three states: 1) the driving signal V C is stable and the V GS voltage reaches the input requirement of the turn-on of the MOS tube, at this time the drain-source of the MOS tube is turned on; 2) the driving signal V C is stable and the V GS voltage reaches the input requirement of the turn-off of the MOS tube, at this time the drain-source of the MOS tube is turned off; 3) the driving signal V C is in the change from high to low or from low to high, at this time the corresponding V GS voltage is also in the change, and the drain-source of the MOS tube is in the transition process of the turn-on or turn-off. The third state is called "transient state", and for the periodic V GSIn applications where control signals are used to control the on / off state of MOSFETs, the transient time is very short compared to a signal cycle.

[0017] For circuits using active semiconductor devices such as MOSFETs for switching control, the MOSFET's on / off state causes current to flow through different paths, resulting in three distinct states: 1) MOSFET drain-source conduction; 2) MOSFET drain-source turn-off; 3) MOSFET in the transition between on and off states. Similarly, the third state is transient and occupies a very short period of the periodic on / off cycle. In the circuit topology, if the switch is off, there is typically a large turn-off voltage drop across the switch, denoted as V. OFF If the switch is closed, the voltage drop across the switch will be very low, denoted as V. ON In a circuit topology, if the drain D of a MOSFET maintains the same voltage V in both circuit states... D (Relative to ground) then the voltage V of the source stage S S V indicates that the service is active. S =V D -V ON V in the off state S =V D -V OFF Therefore, the source voltage V S There is a significant difference between the on and off states. If the source voltage (S) of the MOSFET remains the same in both circuit states... S Then the voltage V of the drain D D V indicates that the service is active. D =V S +V ON V in the off state D =V S +V OFF Therefore, the drain voltage V D There is a significant difference between the on and off states. Other types of switching transistors, such as IGBTs, also exhibit the same characteristics. In the following text, the switching terminal (non-control terminal) that exhibits a larger voltage difference relative to ground in both on and off states is referred to as the "moving point."

[0018] For ease of explanation, the drive signal V C Both the on and off states of the switching transistor are abstracted into logic high and logic low signals. That is, when the switching transistor is in the on or off state, V is... C The state where the relative voltage of the moving point is high is recorded as logic high, and the state where the relative voltage is low is recorded as logic low. Because V CThe logic state change of the V C The state and the dynamic point state have unique logical correlation, and the related signals can be processed by using logic gate devices. If the voltage signal of the V C or the dynamic point is not suitable for direct input into the logic gate circuit, a voltage conversion circuit is needed, which takes the V C or the dynamic point as input and outputs a signal suitable for the input of the logic gate. After level conversion, the V C The related state and the dynamic point related state still have unique logical correlation, and once the topology of the circuit is determined, the V C The relationship between the state and the dynamic point state is one of the following two types:

[0019] Class A Class B V C logic high, causing the moving point logic high V C logic high, causing the moving point logic low V C logic low, causing the moving point logic low V C logic low, causing the moving point logic high

[0020] Taking Class A as an example, in the first state and the second state, the V C and the logic state of the dynamic point should be the same. If the V C and the logic state of the dynamic point are input into the two input XOR gate, the output truth table of the XOR gate is as follows:

[0021]

[0022]

[0023] wherein H represents high level, and L represents low level. In the V C and the switch tube are in transient state, due to the delay of the circuit, when the V C reaches the corresponding logic level, the logic level of the dynamic point cannot be immediately converted to the logic level corresponding to the current V C Therefore, the logic gate will output the opposite state of the normal state during the transient state. The transient state only lasts for a very short time, and a low-pass filter circuit can be added to the output end of the logic gate to filter out the transient state. The detection circuit only responds to abnormalities that exceed the transient time.

[0024] In actual application, only the first state and the second state of the detection circuit can determine whether the working state of the circuit is abnormal.

[0025] When the abnormal state occurs, for example, the dynamic point in the circuit is short-circuited to the voltage source or the reference ground, the dynamic point voltage is affected by the short circuit, and the dynamic point voltage cannot be changed with the V C signal control. Taking Class A as an example

[0026]

[0027] The driving signal Vc is a periodic PWM signal, which periodically switches between high and low levels. Therefore, the short-circuit abnormal condition is always detected. Similarly, after the load is disconnected, the voltage state of the moving point is fixed as high or low, and does not change with the control of Vc, so it can also be detected. Since the load disconnection does not cause large current, there is no requirement for high response time for the protection of disconnection.

[0028] Similarly, for the B class, under normal circumstances, the moving point voltage should also change with the control of the Vc signal. When an abnormal state occurs, such as the moving point in the line being short-circuited to the voltage source or the reference ground, the moving point voltage is affected by the short circuit, and the moving point voltage cannot change with the control of the V C The driving signal Vc is a periodic PWM signal, which periodically switches between high and low levels. Therefore, the short-circuit abnormal condition is always detected. Similarly, after the load is disconnected, the voltage state of the moving point is fixed as high or low, and does not change with the control of Vc, so it can also be detected. Since the load disconnection does not cause large current, there is no requirement for high response time for the protection of disconnection.

[0029] The application will be described in detail below with reference to the drawings and specific embodiments.

[0030] Figure 1 The circuit principle diagram of the load driving circuit with fast protection function according to the first embodiment of the application is shown.

[0031] Please refer to Figure 1 The load driving circuit with fast protection function according to the first embodiment of the application comprises a control circuit, a switching tube M1, a first output terminal S1 and a second output terminal S2.

[0032] The first output terminal S1 and the second output terminal S2 of the load driving circuit are used to connect two ends of the load L respectively, and one of the output terminals is connected with the conduction end of the switching tube as the moving point, and the other output terminal is used to connect the power supply or the ground;

[0033] The output terminal of the control circuit is connected with the control terminal of the switching tube M1, so as to output the PWM signal to the switching tube M1, control the conduction and turn-off of the switching tube M1, and the input terminal of the control circuit is connected with the conduction end of the switching tube M1 as the moving point. The control circuit comprises a detection circuit 11 and a switching tube control circuit 12.

[0034] The detection circuit 11 comprises a voltage conversion circuit 111, a logic circuit 112 and a filter circuit 113. The input terminal of the voltage conversion circuit 111 is connected with the conducting terminal of the switch tube M1 as the moving point, and the voltage conversion circuit 111 is used to convert the voltage of the moving point of the switch tube M1 into the voltage within the working voltage range of the logic circuit 112. The first input terminal of the logic circuit 112 is connected with the output terminal of the voltage conversion circuit 111, and the second input terminal of the logic circuit 112 is connected with the output terminal of the switch tube control circuit 12, and the logic circuit 112 is used to perform logic operation on the voltage signal of the moving point and the PWM signal outputted by the switch tube control circuit 12 to the switch tube M1, and generate a logic level signal. The input terminal of the filter circuit 113 is connected with the output terminal of the logic circuit 112, and the output terminal of the filter circuit 113 is connected with the input terminal of the switch tube control circuit 12. The filter circuit 113 filters the logic level signal outputted by the logic circuit 112, which helps to exclude the influence of the transient state, thereby avoiding misjudgment.

[0035] The output terminal of the switch tube control circuit 12 is connected with the control terminal of the switch tube M1, and the switch tube control circuit 12 is used to determine whether the output of the load driving circuit is abnormal according to the received logic level signal, and the switch tube M1 is closed when the output of the load driving circuit is abnormal.

[0036] In the embodiment, the switch tube M1 is an NMOS tube. The load L is an inductive load, and D1 is a freewheeling diode connected in parallel across the inductive load L. The logic circuit 112 is an XOR gate. The filter circuit 113 is an RC low-pass filter circuit. The switch tube control circuit 12 is an MCU. The gate, drain and source of the NMOS tube respectively constitute the control terminal, the first conducting terminal and the second conducting terminal of the switch tube M1. The drain of the NMOS tube M1 is the moving point and is connected with the inductive load L. The first output terminal S1 of the load driving circuit is connected with the drain of the NMOS tube M1, and the second output terminal S2 of the load driving circuit is connected with the power supply DC.

[0037] The voltage conversion circuit 111 comprises a current limiting resistor R3, a pull-up resistor R4, an NPN transistor Q2 and a voltage conversion circuit power supply Vcc. The current limiting resistor R3 is connected in series between the moving point of the switch tube M1 and the base of the NPN transistor Q2, and the pull-up resistor R4 is connected in series between the voltage conversion circuit power supply Vcc and the collector of the NPN transistor Q2; the collector of the NPN transistor Q2 constitutes the output terminal of the voltage conversion circuit, and the emitter of the NPN transistor Q2 is grounded. The voltage conversion circuit 111 converts the high and low levels of the large amplitude of the moving point to the 0-5V level which can be inputted by the XOR gate XOR. It should be noted that when the voltage of the moving point of the switch tube M1 is within the working voltage range of the logic circuit 112, the voltage conversion circuit 111 is not needed to be set.

[0038] Further, the load driving circuit comprises a current limiting circuit 3 for limiting the current flowing through the switch tube Ml when the current flowing through the switch tube Ml exceeds a preset current threshold. The current limiting circuit limits the maximum current flowing through the switch tube Ml, thus allowing the use of a switch tube Ml with a smaller safe operating range (and lower cost) for abnormality protection, and allowing the detection circuit and the switch tube control circuit to have a longer reaction time, which helps the detection circuit and / or the switch tube control circuit to implement more functions, such as using a filter circuit or a software algorithm to eliminate the influence of a transient state, thus improving the safety of the product and the accuracy of abnormality judgment.

[0039] Optionally, the current limiting circuit 3 is connected between one of the conducting terminals of the switch tube Ml and the ground, and is connected to the control terminal of the switch tube Ml. The current limiting circuit 3 is configured to control the switch tube Ml to have a smaller opening degree when the current flowing through the switch tube Ml exceeds a preset current threshold, so as to limit the current flowing through the switch tube Ml.

[0040] In this embodiment, the current limiting circuit comprises a current sampling resistor Rl and an NPN transistor Ql. One end of the current sampling resistor Rl is connected to the source of the NMOS tube Ml and the base of the NPN transistor Ql, respectively, and the other end of the current sampling resistor Rl is grounded. The collector of the NPN transistor Ql is connected to the gate of the NMOS tube Ml, and the emitter of the NPN transistor Ql is grounded. When current flows through the current sampling resistor Rl, a voltage drop Vrs is established across the current sampling resistor Rl, and this voltage drop Vrs or an appropriately amplified voltage drop A*Vrs (which can be achieved by connecting an operational amplifier circuit 33 between the resistor Rl and the base of the NPN transistor Ql, as shown in FIG. 3) is applied to the base of the NPN transistor Ql. When the conduction current of the switch tube Ml exceeds a preset current threshold, the collector and the emitter of the NPN transistor Ql are turned on, thereby reducing the V Figure 2 of the switch tube Ml, and the conduction current of the switch tube Ml is also reduced due to the influence of V GS . GS The negative feedback system formed by the current sampling resistor Rl, the operational amplifier circuit 33, the NPN transistor Ql, and the switch tube Ml ensures that the conduction current of the switch tube Ml does not exceed V BE / (Rl*A); where V BE is the base conduction voltage of the NPN transistor Ql, and A is the closed-loop amplification of the operational amplifier circuit 33 (when the operational amplifier circuit is not set, the amplification is equivalent to 1), thus the current limiting circuit limits the peak current flowing through the switch tube Ml.

[0041] The resistor R2 controls the opening and closing speed of the switch tube Ml, and also allows the current limiting circuit 3 to limit the current of the switch tube Ml while driving the signal V CWill not be affected. Filtered logic level signal Alarm is the input signal of switch control circuit 12, and the logic level signal is high, which will trigger the interrupt of MCU as switch control circuit 12, and immediately adjust the driving signal V C So that the switch M1 is turned off, and the state of being turned off is maintained, and the abnormal state is latched, even if the abnormal signal disappears due to the corresponding action of the subsequent circuit, the control circuit still maintains the current output state.

[0042] According to Figure 1 the circuit structure in the load driving circuit, when the load driving circuit works normally, the filtered logic level signal Alarm, the driving signal V C , and the moving point signal have the following relationship:

[0043] V C status Moving point status Alarm H L L L H L

[0044] The output of the load driving circuit appears abnormal, including but not limited to the following situations:

[0045] 1) The first output end S1 of the load driving circuit is short-circuited to the input power DC or the inductive load L is short-circuited

[0046] When the switch M1 is turned on, a current higher than that in normal working is generated, the current limiting circuit 3 is triggered, and the on current is limited to the peak current designed at the time. The moving point voltage is short-circuited to the power DC, and it cannot be changed with the control of the driving signal V C .

[0047] The filtered logic level signal Alarm, the driving signal V C , and the moving point signal have the following relationship:

[0048] V C status Moving point status Alarm H H H L H L

[0049] When the switch M1 generates a large current due to the abnormal output of the load driving circuit when it is turned on, first, the current limiting circuit 3 limits the current of the switch M1 within the controllable design current threshold, which is V BE / 0.1 OHM=6A in this embodiment. The 6A current will last, and the high drain-source voltage V DS of the switch M1 forms a large power loss. At the same time, because V C and the state of the moving point are inconsistent with those in normal times, the logic level signal output by the XOR gate is high, which lasts, and the detection circuit can capture the abnormality. The switch control circuit 12 will immediately and continuously output a low-level signal when the Alarm signal is high, and turn off the switch M1.

[0050] 2) The first output end S1 of the load driving circuit is short-circuited to the reference ground

[0051] In this case, the switch tube M1 drain-source is short-circuited, the moving point voltage is short-circuited to the ground, and cannot be changed with the control of the driving signal V C .

[0052] The filtered logic level signal Alarm, the driving signal V C , and the moving point signal have the following relationship:

[0053] V C status Moving point status Alarm H L L L L H

[0054] Therefore, the abnormality can be detected by the detection circuit, and the protection measures are taken by the switch tube control circuit 12. In this abnormality, the switch tube M1 drain-source is short-circuited, and there is no high power loss, so the switch tube M1 is safe.

[0055] In this embodiment, when the switch tube generates a large current because of the abnormal short-circuit of the load driving circuit output end, the current limiting circuit can first limit the peak current to be less than the specification of the switch tube, and then the detection circuit detects the abnormality and completely turns off the switch tube through the switch tube control circuit, so that the switch tube still works in the safe working range of the device in the abnormal condition.

[0056] In this embodiment, the detection circuit directly compares the driving signal Vc and the moving point voltage by using a logic circuit. Since the response speed of the two is fast, and they have different corresponding relationships in the normal working mode and the short-circuit mode, the judgment scheme of the present application has a faster response ability than other judgment methods in the prior art, thereby improving the safety, and the switch tube semiconductor device with a smaller safe working range can be used to realize the abnormal protection, thereby optimizing the cost. In addition, since the detection circuit is an independent circuit, compared with integrating the detection function into the MCU, the cost can be reduced.

[0057] Figure 3 The circuit principle diagram of the load driving circuit with the fast protection function according to the second embodiment of the present application is shown.

[0058] The second embodiment and the first embodiment the most important difference is that the load driving circuit switch M1 used is not NMOS tube, but PMOS tube. For this, the load driving circuit is provided with a PMOS tube driving circuit composed of resistance R6, resistance R7, resistance R8 and NPN transistor Q3. The gate, source and drain of the PMOS tube constitute the control end, the first conduction end and the second conduction end of the switch respectively. The drain of the PMOS tube serves as the moving point. One end of the current sampling resistor R1 of the current limiting circuit 3 is connected with the source of the PMOS tube and the base of the PNP transistor Q1 respectively, and the other end of the current sampling resistor R1 is connected with the power supply DC and the emitter of the PNP transistor Q1 respectively. The collector of the PNP transistor Q1 is connected with the gate of the PMOS tube. The second output end S2 of the load driving circuit is connected with the drain of the PMOS tube, and the first output end S1 of the load driving circuit is used for connecting with the ground.

[0059] One end of the resistance R6 is connected with the power supply DC and the emitter of the PNP transistor Q1 respectively, the other end of the resistance R6 is connected with one end of the resistance R7, the collector of the PNP transistor Q1 and the gate of the PMOS tube M1 respectively, the other end of the resistance R7 is connected with the collector of the NPN transistor Q3, and the emitter of the NPN transistor Q3 is grounded. One end of the resistance R8 is connected with the output end of the switch control circuit 12, and the other end of the resistance R8 is connected with the base of the NPN transistor Q3.

[0060] According to the circuit structure in Figure 3 , when the load driving circuit works normally, the filtered logic level signal Alarm, the driving signal V C and the moving point signal have the following relationship:

[0061] V C status Moving point status Alarm H H H L L H

[0062] The output of the load driving circuit appears abnormal, including but not limited to the following situations:

[0063] 1) The second output end S2 of the load driving circuit (i.e. the moving point of the switch) is short-circuited to the reference ground or the load L is short-circuited

[0064] When the switch M1 is turned on, the current will be higher than that in normal working, and the current limiting circuit 3 will be triggered to limit the conduction current to the peak current designed at the time. The moving point voltage is short-circuited to the reference ground, and it cannot be changed with the control of the driving signal V C .

[0065] The filtered logic level signal Alarm, the driving signal V C and the moving point signal have the following relationship:

[0066] V C status Moving point status Alarm H L L L L H

[0067] When the switch tube Ml generates a large current because of the abnormal output of the load driving circuit when it is turned on, first, the current limiting circuit 3 limits the current of the switch tube Ml within a controllable design current threshold, which is V BE 0.1 OHM = 6A. The 6A current will continue, and the high drain-source voltage V DS of the switch tube Ml will form a large power loss. At the same time, because V C and the state of the moving point do not match the normal state, the logic level signal output by the XOR gate XOR is low, which continues, and the detection circuit can capture the abnormality. The switch tube control circuit 12 will immediately continue to output a low level signal when the Alarm signal is low, turning off the switch tube Ml.

[0068] 2) If the second output end S2 of the load driving circuit is short-circuited to the input voltage source,

[0069] In this case, the drain-source of the switch tube Ml is short-circuited, and the moving point voltage is short-circuited to the input power DC and cannot be changed with the control of the driving signal V C .

[0070] The filtered logic level signal Alarm, the driving signal V C , and the moving point signal have the following relationship:

[0071] V C status Moving point status Alarm H H H L H L

[0072] Therefore, the abnormality can be detected by the detection circuit, and protective measures are taken by the switch tube control circuit 12. In this abnormality, the drain-source of the switch tube Ml is short-circuited, and there is no high power loss, so the switch tube Ml is safe.

[0073] Figure 4 A circuit principle diagram of a load driving circuit with a fast protection function according to a third embodiment of the present application is shown.

[0074] The main difference between the third embodiment and the first embodiment is that the first embodiment uses a hardware logic gate circuit in the detection circuit to detect abnormal conditions of the output of the load driving circuit, while the third embodiment uses a software method to achieve this.

[0075] Among them, the control circuit 1 includes a voltage conversion circuit 111 and a switch tube control circuit 12.

[0076] The input end of the voltage conversion circuit 111 is connected with the conduction end of the switch tube Ml as the moving point (the drain of the NMOS tube Ml in this embodiment), and the voltage conversion circuit is used to convert the voltage of the moving point of the switch tube Ml into the working voltage range of the switch tube control circuit 12. The circuit structure of the voltage conversion circuit 111 is the same as that of the first embodiment. When the voltage of the moving point of the switch tube Ml is within the working voltage range of the switch tube control circuit 12, the voltage conversion circuit 111 is not needed.

[0077] The input end of the switch tube control circuit 12 is connected with the output end of the voltage conversion circuit 111, and the output end of the switch tube control circuit 12 is connected with the control end of the switch tube Ml; the switch tube control circuit 12 is used to determine whether the output of the load driving circuit is abnormal according to the voltage signal of the moving point and the PWM signal outputted by the switch tube control circuit 12 to the switch tube Ml, and to close the switch tube Ml when the output of the load driving circuit is abnormal. The switch tube control circuit 12 can be an MCU.

[0078] When the output of the load driving circuit is normal, the driving signal Vc and the voltage signal of the moving point have a certain corresponding relationship. In this embodiment, the switch tube control circuit 12 pre-stores the level state of the driving signal Vc and the voltage signal of the moving point when the output of the load driving circuit is in the normal working condition, and compares the real-time collected voltage signal of the moving point and the level state of the PWM signal outputted to the switch tube Ml with the pre-stored level state when the load driving circuit is working. If the two are not consistent, and the maintaining time of the inconsistent state reaches a predetermined time, it is determined that the output of the load driving circuit is abnormal.

[0079] Further, the MCU records the time Tl when the level state of the driving signal Vc (i.e. the PWM signal outputted by the switch tube control circuit 12 to the switch tube Ml) is converted, and records the time T2 when the level state of the moving point voltage signal of the switch tube is converted. If the value of T2-Tl is within the set time threshold range, it is determined that the output of the load driving circuit is normal. If the level state of the moving point voltage signal of the switch tube is not detected to be converted within the predetermined time from the time Tl, or T2-Tl exceeds the time threshold, it is determined that the output of the load driving circuit is abnormal. The determination of the time threshold can be achieved by the following method, i.e. through the actual debugging of the circuit, the delay time of the circuit under various environments (different environmental temperature, input voltage, load size, etc.) is measured, the delay time starts from the conversion of the level state of the driving signal Vc, and ends when the conversion of the level state of the moving point signal of the switch tube is completed. The time threshold set by the MCU needs to be greater than the delay time, and the smaller the time threshold, the faster the response of the abnormal detection. The function of the time threshold is similar to that of the filter circuit in the foregoing detection circuit.

[0080] The output abnormality detection of the load driving circuit is realized by pure software, which has faster operation speed than the XOR gate and the filter circuit, and has the advantages of flexibility and low delay.

[0081] The switch tube M1 of the third embodiment adopts the structure of NMOS tube, as shown in Figure 5 The structure of the switch tube M1 and the current limiting circuit in the third embodiment can be modified to be the same as the second embodiment (i.e. adopting PMOS tube and using the corresponding current limiting circuit structure in the second embodiment), thereby constructing the fourth embodiment of the present application.

[0082] When the voltage of the moving point of the switch tube M1 is within the working voltage range of the switch tube control circuit, the voltage conversion circuit is not needed, as shown in 6, Figure 6 In the embodiment shown in the figure, the voltage conversion circuit is cancelled, and the function realized by the control circuit 1 in this embodiment is the same as that of the switch tube control circuit in the third embodiment.

[0083] In other embodiments, IGBT tube can also be used as the switch tube, and the drain of the IGBT tube can be used as the moving point. In addition, the logic circuit is not limited to being composed of XOR gate, and XNOR gate can also be used, and the output of the XNOR gate is opposite to that of the XOR gate.

[0084] According to another embodiment of the present application, a fast protection method of the load driving circuit is also provided, which comprises the following steps: judging whether the output of the load driving circuit is abnormal according to the voltage signal of the moving point and the PWM signal output from the control circuit to the switch tube, and closing the switch tube when the output of the load driving circuit is abnormal.

[0085] Obviously, those skilled in the art can make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application belong to the scope of the claims of the present application and their equivalent technologies, the present application also intends to include these modifications and variations.

Claims

1. A load drive circuit with fast protection function, comprising a control circuit, a switching transistor, a first output terminal, and a second output terminal; the switching transistor has a control terminal, a first conducting terminal, and a second conducting terminal; the output terminal of the control circuit is connected to the control terminal of the switching transistor to output a PWM signal to the switching transistor to control the switching transistor's on and off states; the first and second output terminals of the load drive circuit are respectively connected to the two ends of a load, and one output terminal is connected to the conducting terminal of the switching transistor that serves as a moving point, and the other output terminal is connected to a power supply or ground; characterized in that, The input terminal of the control circuit is connected to the conducting terminal of the switching transistor that serves as the moving point. The control circuit is used to determine whether the output of the load drive circuit is abnormal based on the voltage signal of the moving point and the PWM signal output by the control circuit to the switching transistor. When the output of the load drive circuit is abnormal, the switching transistor is turned off. The control circuit includes a detection circuit and a switching transistor control circuit; the detection circuit includes a logic circuit and a filtering circuit; the logic circuit is an XOR gate or a XNOR gate; the first input terminal of the logic circuit is connected to the conducting terminal of the switching transistor that serves as the moving point, and the second input terminal of the logic circuit is connected to the output terminal of the switching transistor control circuit. The logic circuit is used to perform logical operations on the voltage signal of the moving point and the PWM signal output by the switching transistor control circuit to the switching transistor, and generate a logic level signal; the input terminal of the filtering circuit is connected to the output terminal of the logic circuit, and the output terminal of the filtering circuit is connected to the input terminal of the switching transistor control circuit; the output terminal of the switching transistor control circuit is connected to the control terminal of the switching transistor. The switching transistor control circuit is used to determine whether the output of the load drive circuit is abnormal based on the received logic level signal, and shuts down the switching transistor when the output of the load drive circuit is abnormal.

2. The load drive circuit with fast protection function according to claim 1, characterized in that, The detection circuit includes a voltage conversion circuit. The input terminal of the voltage conversion circuit is connected to the conducting terminal of the switching transistor that serves as the moving point, and the output terminal of the voltage conversion circuit is connected to the first input terminal of the logic circuit. The voltage conversion circuit is used to convert the voltage of the moving point of the switching transistor into a voltage within the operating voltage range of the logic circuit.

3. The load drive circuit with fast protection function according to claim 2, characterized in that, The voltage conversion circuit includes a current-limiting resistor, a pull-up resistor, an NPN transistor, and a power supply for the voltage conversion circuit. The current-limiting resistor is connected in series between the moving point of the switching transistor and the base of the NPN transistor, and the pull-up resistor is connected in series between the power supply for the voltage conversion circuit and the collector of the NPN transistor. The collector of the NPN transistor forms the output terminal of the voltage conversion circuit, and the emitter of the NPN transistor is grounded.

4. The load drive circuit with fast protection function according to claim 1, characterized in that, The switching transistor control circuit is an MCU.

5. The load drive circuit with fast protection function according to any one of claims 1 to 4, characterized in that, The switching transistor is a MOSFET or an IGBT, and the drain of the MOSFET or IGBT serves as the moving point.

6. The load drive circuit with fast protection function according to any one of claims 1 to 4, characterized in that, The load drive circuit described is an inductive load drive circuit.

7. The load drive circuit with fast protection function according to any one of claims 1 to 4, characterized in that, The load drive circuit includes a current limiting circuit, which is used to limit the current flowing through the switching transistor when the current flowing through the switching transistor exceeds a preset current threshold.

8. The load drive circuit with fast protection function according to claim 7, characterized in that, The current limiting circuit is connected between one of the conducting terminals of the switching transistor and the power supply or ground, and is connected to the control terminal of the switching transistor. The current limiting circuit is used to control the switching transistor to reduce its opening degree when the current flowing through the switching transistor exceeds a preset current threshold, so as to limit the current flowing through the switching transistor.

9. The load drive circuit with fast protection function according to claim 8, characterized in that, The switching transistor is an NMOS transistor, and the gate, drain, and source of the NMOS transistor constitute the control terminal, the first conduction terminal, and the second conduction terminal of the switching transistor, respectively; one output terminal of the load driving circuit is connected to the drain of the NMOS transistor, and the other output terminal of the load driving circuit is used to connect to the power supply. The current limiting circuit includes a current sampling resistor and an NPN transistor; one end of the current sampling resistor is connected to the source of the NMOS transistor and the base of the NPN transistor, and the other end of the current sampling resistor is grounded; the collector of the NPN transistor is connected to the gate of the NMOS transistor, and the emitter of the NPN transistor is grounded.

10. The load drive circuit with fast protection function according to claim 8, characterized in that, The switching transistor is a PMOS transistor, and the gate, source, and drain of the PMOS transistor constitute the control terminal, the first conduction terminal, and the second conduction terminal of the switching transistor, respectively; one output terminal of the load driving circuit is connected to the drain of the PMOS transistor, and the other output terminal of the load driving circuit is used to connect to ground. The current limiting circuit includes a current sampling resistor and a PNP transistor; one end of the current sampling resistor is connected to the source of the PMOS transistor and the base of the PNP transistor, respectively, and the other end of the current sampling resistor is connected to the power supply and the emitter of the PNP transistor, respectively; the collector of the PNP transistor is connected to the gate of the PMOS transistor.

11. A load drive circuit with fast protection function, comprising a control circuit, a switching transistor, a first output terminal, and a second output terminal; the switching transistor has a control terminal, a first conducting terminal, and a second conducting terminal; the output terminal of the control circuit is connected to the control terminal of the switching transistor to output a PWM signal to the switching transistor to control the switching transistor's on and off states; the first and second output terminals of the load drive circuit are respectively connected to the two ends of a load, and one output terminal is connected to the conducting terminal of the switching transistor that serves as a moving point, and the other output terminal is connected to a power supply or ground; characterized in that... The input terminal of the control circuit is connected to the conducting terminal of the switching transistor that serves as the moving point. The control circuit is used to determine whether the output of the load drive circuit is abnormal based on the voltage signal of the moving point and the PWM signal output by the control circuit to the switching transistor. When the output of the load drive circuit is abnormal, the switching transistor is turned off. The control circuit records the time when the level state of the PWM signal output to the switching transistor changes (T1) and the time when the level state of the dynamic point voltage signal of the switching transistor changes accordingly (T2). If the value of T2-T1 is within the set time threshold range, the output of the load drive circuit is judged to be normal. If no level state change of the dynamic point voltage signal of the switching transistor is detected within a predetermined time from time T1, or if T2-T1 exceeds the time threshold, the output of the load drive circuit is judged to be abnormal.

12. The load drive circuit with fast protection function according to claim 11, characterized in that, The control circuit includes a voltage conversion circuit and a switching transistor control circuit; The input terminal of the voltage conversion circuit is connected to the conducting terminal of the switching transistor that serves as the moving point. The voltage conversion circuit is used to convert the voltage of the moving point of the switching transistor into a voltage range within the operating voltage range of the switching transistor control circuit. The input terminal of the switching transistor control circuit is connected to the output terminal of the voltage conversion circuit, and the output terminal of the switching transistor control circuit is connected to the control terminal of the switching transistor. The switching transistor control circuit records the time when the level state of the PWM signal output to the switching transistor changes (T1) and the time when the level state of the dynamic point voltage signal of the switching transistor changes (T2). If the value of T2-T1 is within the set time threshold range, the output of the load drive circuit is judged to be normal. If no corresponding change in the level state of the dynamic point voltage signal of the switching transistor is detected within a predetermined time from time T1, or if T2-T1 exceeds the time threshold, the output of the load drive circuit is judged to be abnormal.

13. The load drive circuit with fast protection function according to claim 12, characterized in that, The voltage conversion circuit includes a current-limiting resistor, a pull-up resistor, an NPN transistor, and a power supply for the voltage conversion circuit. The current-limiting resistor is connected in series between the moving point of the switching transistor and the base of the NPN transistor, and the pull-up resistor is connected in series between the power supply for the voltage conversion circuit and the collector of the NPN transistor. The collector of the NPN transistor forms the output terminal of the voltage conversion circuit, and the emitter of the NPN transistor is grounded.

14. The load drive circuit with fast protection function according to claim 12, characterized in that, The switching transistor control circuit is an MCU.

15. The load drive circuit with fast protection function according to any one of claims 11 to 14, characterized in that, The switching transistor is a MOSFET or an IGBT, and the drain of the MOSFET or IGBT serves as the moving point.

16. The load drive circuit with fast protection function according to any one of claims 11 to 14, characterized in that, The load drive circuit described is an inductive load drive circuit.

17. The load drive circuit with fast protection function according to any one of claims 11 to 14, characterized in that, The load drive circuit includes a current limiting circuit, which is used to limit the current flowing through the switching transistor when the current flowing through the switching transistor exceeds a preset current threshold.

18. The load drive circuit with fast protection function according to claim 17, characterized in that, The current limiting circuit is connected between one of the conducting terminals of the switching transistor and the power supply or ground, and is connected to the control terminal of the switching transistor. The current limiting circuit is used to control the switching transistor to reduce its opening degree when the current flowing through the switching transistor exceeds a preset current threshold, so as to limit the current flowing through the switching transistor.

19. The load drive circuit with fast protection function according to claim 18, characterized in that, The switching transistor is an NMOS transistor, and the gate, drain, and source of the NMOS transistor constitute the control terminal, the first conduction terminal, and the second conduction terminal of the switching transistor, respectively; one output terminal of the load driving circuit is connected to the drain of the NMOS transistor, and the other output terminal of the load driving circuit is used to connect to the power supply. The current limiting circuit includes a current sampling resistor and an NPN transistor; one end of the current sampling resistor is connected to the source of the NMOS transistor and the base of the NPN transistor, and the other end of the current sampling resistor is grounded; the collector of the NPN transistor is connected to the gate of the NMOS transistor, and the emitter of the NPN transistor is grounded.

20. The load drive circuit with fast protection function according to claim 18, characterized in that, The switching transistor is a PMOS transistor, and the gate, source, and drain of the PMOS transistor constitute the control terminal, the first conduction terminal, and the second conduction terminal of the switching transistor, respectively; one output terminal of the load driving circuit is connected to the drain of the PMOS transistor, and the other output terminal of the load driving circuit is used to connect to ground. The current limiting circuit includes a current sampling resistor and a PNP transistor; one end of the current sampling resistor is connected to the source of the PMOS transistor and the base of the PNP transistor, respectively, and the other end of the current sampling resistor is connected to the power supply and the emitter of the PNP transistor, respectively; the collector of the PNP transistor is connected to the gate of the PMOS transistor.

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