Diagnostic circuit for power drive circuit

Abstract

A diagnostic circuit for a power drive circuit includes a current sampling circuit, a current information processing circuit and a comparison diagnostic circuit. The current sampling circuit is used to collect a current I1 flowing from the positive electrode of a power supply into a current inflow terminal of the power drive circuit, and output a first voltage signal V I1 , and collect the current I2 flowing from the current outflow end of the power driving circuit into the negative electrode of the power supply, and output a second voltage signal V I2 The current information processing circuit is used to process the first voltage signal V I1 and the second voltage signal V I2 The comparison diagnostic circuit is used to determine whether the voltage Vc is greater than the voltage upper limit V TH1 And whether it is less than the voltage lower limit V TH2 , when Vc is greater than V TH1 and Vc is less than V TH2 The present invention can quickly detect and respond to abnormalities in the output of the power drive circuit when the abnormalities occur.

Description

Technical Field

[0001] The invention relates to a protection technology for a power drive circuit. Background Art

[0002] Power drive circuits are often used in electronic products. The load of the power drive circuit can be a pure resistive load, an inductive load, or a capacitive load. In actual applications or product functions, the product is required to be able to protect under abnormal load conditions, such as the output port of the power drive circuit being short-circuited to the ground, short-circuited to the voltage source, or the output current is too large, etc. Therefore, the power drive circuit needs to have a corresponding protection function design to detect these abnormal working conditions and quickly respond to protection. Summary of the invention

[0003] The technical problem to be solved by the present invention is to provide a diagnostic circuit for a power drive circuit, which can quickly detect the abnormality and respond when an abnormal situation occurs in the output of the power drive circuit, such as a short circuit or open circuit at the output end of the drive circuit.

[0004] According to the diagnostic circuit of the power driving circuit of the embodiment of the present invention, the power driving circuit includes a current inflow end, a current outflow end, a first output end and a second output end; the current inflow end and the current outflow end are respectively used to connect to the positive electrode and the negative electrode of the power supply, and the first output end and the second output end are respectively used to connect to the first end and the second end of the load; the diagnostic circuit includes: a current sampling circuit, which is used to collect the current I1 flowing from the positive electrode of the power supply into the current inflow end of the power driving circuit, and output a first voltage signal V related to the current I1 I1 , and collect the current I2 flowing from the current outflow end of the power driving circuit to the negative electrode of the power supply, and output a second voltage signal V related to the current I2 I2 A current information processing circuit, wherein the input end of the current information processing circuit is connected to the output end of the current sampling circuit, and is used to process the first voltage signal V I1 and the second voltage signal V I2 Processing, output voltage Vc, Vc = V REF +(I1-I2)*A,V REF is the reference voltage, A is the amplification factor; a comparison diagnostic circuit, the input end of the comparison diagnostic circuit is connected to the output end of the current information processing circuit, and is used to determine whether the voltage Vc is greater than the preset voltage upper limit V TH1 , and whether it is less than the preset voltage lower limit V TH2 , when Vc is greater than V TH1 The first diagnostic signal is generated when Vc is less than V TH2 A second diagnostic signal is generated.

[0005] The present invention has at least the following technical effects:

[0006] 1. The diagnostic circuit of the embodiment of the present invention generates a first diagnostic signal when the high-end current I1 of the power driving circuit is much larger than the low-end current I2, and generates a second diagnostic signal when the low-end current I2 of the power driving circuit is much larger than the high-end current I1, thereby providing reliable abnormal detection of load current flowing to the wrong circuit network, the output end of the power driving circuit short-circuiting to the power supply, and the output end of the power driving circuit short-circuiting to the ground, thereby improving the reliability of the power driving circuit;

[0007] 2. The diagnostic circuit of the embodiment of the present invention is easy to adjust the protection threshold, thus having good flexibility. BRIEF DESCRIPTION OF THE DRAWINGS

[0008] In order to more clearly illustrate the technical solutions in the embodiments of the present invention, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0009] Figure 1 A circuit schematic diagram of a diagnostic circuit of a power driving circuit according to an embodiment of the present invention is shown.

[0010] Figures 2 to 5 Schematic diagrams of four different types of power driving circuits to which the diagnostic circuit according to the embodiment of the present invention is applicable are shown respectively and exemplarily.

[0011] Figure 6 Four abnormal conditions of the low-side switch driving circuit are shown.

[0012] Figures 7 to 9 The upper voltage limit V is determined respectively. TH1 and the voltage lower limit V TH2 The principle.

[0013] Fig.10 A circuit diagram showing a first specific implementation of a diagnostic circuit according to an embodiment of the present invention is shown.

[0014] Fig.11 A circuit diagram of a second specific implementation of the diagnostic circuit according to an embodiment of the present invention is shown. DETAILED DESCRIPTION

[0015] Figure 1 A circuit schematic diagram of a diagnostic circuit of a power driving circuit according to an embodiment of the present invention is shown.

[0016] Among them, the power driving circuit 100 includes a current inflow terminal A1, a current outflow terminal A2, a first output terminal O1 and a second output terminal O2; the current inflow terminal A1 and the current outflow terminal A2 are respectively used to connect to the positive and negative poles of the power supply Vin, and the first output terminal O1 and the second output terminal O2 are respectively used to connect to the first and second ends of the load 200.

[0017] The diagnosis circuit includes a current sampling circuit, a current information processing circuit 2 and a comparison diagnosis circuit 3.

[0018] The current sampling circuit includes a high-end current sampling circuit 11 and a low-end current sampling circuit 12. The high-end current sampling circuit 11 is used to collect the current I1 flowing from the positive electrode of the power supply Vin into the current inflow terminal A1 of the power driving circuit, and output a first voltage signal V related to the current I1. I1 The low-end current sampling circuit 12 collects the current I2 returned from the current outflow terminal A2 of the power driving circuit to the negative electrode of the power supply Vin, and outputs a second voltage signal V related to the current I2. I2 .

[0019] The input terminal of the current information processing circuit 2 is connected to the output terminal of the current sampling circuit, and is used to process the first voltage signal V I1 and the second voltage signal V I2 Processing, output voltage Vc, Vc = V REF +(I1-I2)*A,V REF is the reference voltage, and A is the amplification factor.

[0020] The input terminal of the comparison diagnosis circuit 3 is connected to the output terminal of the current information processing circuit 2 to determine whether the voltage Vc is greater than the preset voltage upper limit V TH1 , and whether it is less than the preset voltage lower limit V TH2 , when Vc is greater than V TH1 And Vc is less than V TH2 A diagnostic signal is generated at all times.

[0021] Figure 1 In the embodiment, the output driving current Iout of the power driving circuit 100 is output from the first output terminal O1, flows through the load 200, and then flows into the power driving circuit 100 from the second output terminal O2. The input current I1 of the power driving circuit 100 is supplied by the power supply Vin, flows into the power driving circuit 100 through the current inflow terminal A1, and the return current I2 of the power driving circuit 100 flows out through the current outflow terminal A2 and returns to the negative electrode of the power supply Vin.

[0022] The power driving circuit 100 and the load 200 can have various forms. For example, the power driving circuit 100 can be a high-side switch driving circuit, a low-side switch driving circuit, a full-bridge driving circuit, etc. The load 200 can be a pure resistance load, an inductive load, or a capacitive load. The requirement for the current sampling circuit is that it can always collect all the high-end currents from A0 to A1 and the low-end currents from A2 to the negative electrode of the power supply Vin. Figure 1 According to the characteristics of the lumped circuit and Kirchhoff's current law, the current flowing into terminal A1 is always equal to the current flowing out of terminal A2, that is, I1=I2.

[0023] Figures 2 to 5 Schematic diagrams of four different types of power driving circuits to which the diagnostic circuit according to the embodiment of the present invention is applicable are shown respectively and exemplarily.

[0024] Figure 2 In the embodiment, the power driving circuit 100 is a high-side switch driving circuit. Figure 2 The switch device S1 and the freewheeling diode D1 are shown. When the load 200 is an inductive load, the freewheeling diode D1 is required for freewheeling. When the load 200 is a pure resistance or capacitive load, the freewheeling diode D1 may not be required.

[0025] Figure 3 In the embodiment, the power driving circuit 100 is a low-side switch driving circuit. Figure 2 The switch device S2 and the freewheeling diode D2 are shown. When the load 200 is an inductive load, the freewheeling diode D2 is required for freewheeling. When the load 200 is a pure resistance or capacitive load, the freewheeling diode D2 may not be required.

[0026] Figure 4 and Figure 5 In the figure, the power driving circuits 100 are two different types of full-bridge driving circuits, wherein S1, S2, S3, and S4 are switching devices, and D3 and D4 are freewheeling diodes.

[0027] When the structure of the power drive circuit is determined, the influence of the current at the output end of the power drive circuit on the equal relationship between I1 and I2 when an abnormal condition occurs in the power drive circuit can be analyzed by combining the circuit structure. Figure 6 As shown, taking the power drive circuit as a low-side switch drive circuit as an example:

[0028] Case I: The first output terminal O1 of the power driving circuit 100 is externally short-circuited to a voltage higher than the original first output terminal O1, or a current is externally injected into the first output terminal O1. Assuming that the injected current is I3, according to Kirchhoff's current law, no matter whether the switch device S2 is turned on or off, there is always a current relationship I3 = I2-I1. It can be seen that the larger I3 is, the greater the difference between I1 and I2 is;

[0029] Case II: The first output terminal O1 of the power driving circuit 100 is externally short-circuited to a voltage lower than the original first output terminal O1, or a current is externally drawn from the first output terminal O1. Assuming that the drawn current is I4, no matter whether the switch device S2 is turned on or off, there is always a current relationship I4 = I1-I2. It can be seen that the larger I4 is, the greater the difference between I1 and I2 is.

[0030] Case III: The second output terminal O2 of the power driving circuit 100 is externally short-circuited to a voltage higher than the original second output terminal O2, or a current is externally injected into the second output terminal O2. Assuming that the injected current is I5, no matter whether the switch device S2 is turned on or off, there is always a current relationship I5 = I2-I1. It can be seen that the larger I5 is, the greater the difference between I1 and I2 is.

[0031] Case IV: The second output terminal O2 of the power driving circuit 100 is externally short-connected to a voltage lower than the original second output terminal O2, or a current is externally drawn from the second output terminal O2. Assuming that the drawn current is I6, no matter whether the switch device S2 is turned on or off, there is always a current relationship I6 = I1-I2. It can be seen that the larger I6 is, the greater the difference between I1 and I2 is.

[0032] The current information processing circuit 2 is a differential amplifier circuit that converts the collected first voltage signal V I1 and the second voltage signal V I2 After circuit processing, the output voltage Vc=V REF +(I1-I2)*A, the amplification factor A is the amplification factor of the differential amplifier circuit output voltage relative to the input imbalance current (I1-I2), V REF It is the default voltage of the differential amplifier circuit when the input imbalance current (I1-I2) = 0. If the power drive circuit and load are normal, I1 = I2, Vc = V REF If the load port encounters an abnormal situation, such as the above situation I, a current I3 is injected from the first output terminal O1 to the power drive circuit through the external circuit, and the circuit structure cannot satisfy I1=I2, I3=I2-I1, the Vc voltage value will deviate from the reference voltage V REF . Vc=V REF -I3*A, the larger I3 is, the more the Vc voltage value deviates from the reference voltage V REF The greater the amplitude.

[0033] The comparison diagnosis circuit 3 compares the voltage Vc with the preset voltage range. TH1 When I1 is judged to be higher than I2 than the expected range, the first diagnostic signal Alarm1 is generated. <V TH2When it is determined that I2 is higher than I1 by an expected range, a second diagnostic signal Alarm2 is generated. The first diagnostic signal Alarm1 and the second diagnostic signal Alarm2 can serve as an alarm. Figures 7 to 9 , the preset voltage upper limit V in this embodiment TH1 and the voltage lower limit V TH2 The determination process is as follows:

[0034] 1) Determine the fluctuation range of voltage Vc when the circuit is working normally (I1 = I2). At this time, Vc = Vcnormal. Due to the non-ideality of the current sampling circuit and the current information processing circuit, Vcnormal is relative to V REF There will be fluctuations. According to the circuit error analysis, it can be obtained that within the defined working range, V REFMIN <Vcnormal<V REFMAX ;

[0035] 2) Determine the minimum and maximum differences between I1 and I2 required to generate a diagnostic signal. D1 It is the minimum amplitude of I1-I2 required to trigger the alarm when I1 is greater than I2, that is, V TH1 =V REFMAX +I D1 *A,I D2 It is the minimum amplitude of I2-I1 required to trigger the alarm when I2 is greater than I1, that is, V TH2 =V REFMIN –I D2 *A;I D3 It is the maximum I1-I2 amplitude required to trigger the I1 greater than I2 alarm, that is, V TH1 =V REFMIN +I D3 *A;I D4 It is the maximum I2-I1 amplitude required to trigger the I2 greater than I1 alarm, that is, V TH2 =V REFMAX –I D4 *A.

[0036] The circuit is such that I1 is at least I greater than I2. D1 When V TH1 Generate the first diagnostic signal Alarm1, I2 is at least I greater than I1 D2 When V TH2 The second diagnostic signal Alarm2 is generated. Using this setting will ensure that when the absolute value of the difference between I1 and I2 is less than I D1 and I D2 When the absolute value of the difference between I1 and I2 is greater than I D3 or I D4Only when the load is abnormal can the diagnostic signal be triggered, ensuring that the diagnostic circuit can respond normally and generate an alarm.

[0037] The principle and working process of the present invention are described in more detail below in combination with two specific implementations.

[0038] First specific embodiment

[0039] Please refer to Fig.10 In this embodiment, the load 200 is an inductive load, the switch device S2 may be, for example, a MOSFET, and the freewheeling diode D2 provides a freewheeling path for the load when the switch device S2 is turned off.

[0040] The high-end current sampling circuit 11 includes a current sampling resistor Shunt1, the current input terminal and the current output terminal of the current sampling resistor Shunt1 are respectively connected to the positive electrode of the power source Vin and the current inflow terminal A1 of the power driving circuit 100, and the first voltage signal V is output from the current input terminal and the current output terminal of the current sampling resistor Shunt1. I1 The low-end current sampling circuit 12 includes a current sampling resistor Shunt2, one end of which is connected to the current outflow terminal A2 of the power driving circuit 100, the other end of which is connected to the negative electrode of the power supply, and one end of which outputs a second voltage signal V I2 .

[0041] The current information processing circuit 2 includes an operational amplifier U1, a resistor R5, a resistor R6, a resistor network, and a reference voltage source 21. The output voltage of the reference voltage source 21 is V REF The resistor network includes a first series branch and a second series branch. The first series branch includes resistors R1 and R2 connected in series, and the second series branch includes resistors R3 and R4 connected in series. The two ends of the first series branch are respectively connected to the current input terminal P1 of the current sampling resistor Shunt1 and the negative electrode of the power supply Vin; the two ends of the second series branch are respectively connected to the current output terminal P2 of the current sampling resistor Shunt1 and one end P3 of the current sampling resistor Shunt2; the common point P4 of the resistor R1 and the resistor R2 is connected to the common point of one end of the resistor R6 and the in-phase input terminal of the operational amplifier U1, and the common point P5 of the resistor R3 and the resistor R4 is connected to the common point of one end of the resistor R5 and the inverting input terminal of the operational amplifier U1; the other end of the resistor R5 is connected to the output terminal of the operational amplifier U1, the other end of the resistor R6 is connected to the positive electrode of the reference voltage source 21, and the negative electrode of the reference voltage source 21 is connected to the negative electrode of the power supply Vin; the output terminal of the operational amplifier U1 is connected to the input terminal of the comparison diagnosis circuit 3.

[0042] Current sampling resistors Shunt1 and Shunt2 are precision current sampling resistors, and their resistance values ​​are at the level of tens of mOhm, and in this embodiment, they are all 50mohm. Resistors R1, R2, R3 and R4 form a resistor network, and their resistance values ​​are at the level of KOhm, and in this embodiment, they are all 10Kohm. The internal resistance of the voltage signal on the current sampling resistor Shunt1 and the current sampling resistor Shunt2 is much smaller than the resistor network, and it can be approximated that the current flowing through the current sampling resistor Shunt1 all flows through the first output terminal O1, and the current flowing through the current sampling resistor Shunt2 all flows through the second output terminal O2. The current in the circuit is indicated as shown in the figure, I1 is the current flowing through the current sampling resistor Shunt1, I2 is the current flowing through the current sampling resistor Shunt2, and Iout is the current flowing through the load 200. The arrow direction in the figure is defined as the positive direction of the current. Node P4 is connected to the non-inverting input terminal of the operational amplifier U1, and node P5 is connected to the inverting input terminal of the operational amplifier U1. The output of the current information processing circuit 2 is the output voltage signal Vc of the operational amplifier U1.

[0043] The comparison diagnosis circuit 3 is a window comparison circuit, including voltage comparators U2, U3, resistors R7, R8, R9, R10 and R11. Voltage comparators U2 and U3 are output open-drain / open-collector voltage comparators. The output of voltage comparator U2 is pulled up to a 5V voltage source through resistor R7, and the output of voltage comparator U3 is pulled up to another 5V voltage source through resistor R11. VCC is a voltage source, and resistors R8, R9 and R10 form a voltage-dividing resistor network. By adjusting the resistance values ​​of resistors R8, R9 and R10 appropriately, a suitable voltage upper limit V can be obtained. TH1 and the voltage lower limit V TH2 . Voltage lower limit V TH2 Connected to the inverting input of the voltage comparator U3, the upper voltage limit V TH1 Connected to the non-inverting input terminal of the voltage comparator U2. The output terminal of the current information processing circuit 2 is connected to the inverting input terminal of the voltage comparator U2 and the non-inverting input terminal of U3 respectively. The function of the window comparison circuit is: when Vc>V TH1 The first diagnostic signal Alarm1 is output when Vc <V TH2 The second diagnostic signal Alarm2 is outputted when the first diagnostic signal Alarm1 and the second diagnostic signal Alarm2 are both low level signals. In this embodiment, R1=R2=R3=R4=10K, the op amp U1 adopts the general voltage op amp of TI, model LM2904A, and the voltage comparators U2 and U3 adopt the voltage comparator of TI, model LM2903. The op amp U1, the voltage comparator U2, and the voltage comparator U3 are powered by a single 10V power supply. The reference voltage V REFis 5V, R5=R6=100K, the circuit closed loop gain of op amp U1 is A CL =20. The resistance of current sampling resistors Shunt1 and Shunt2 is R shunt1 , R shunt2 The output voltage Vc of the operational amplifier U1 in this embodiment has an amplification factor of A=A relative to the input unbalanced current (I1-I2). CL *R shunt1 =20*50mohm=1,Vc=V REF +(I1-I2)*1=5+(I1-I2), based on the above analysis of normal operation and four abnormal conditions, the signal voltage of Vc is:

[0044]

[0045] Vccase1 to Vccase4 are voltage values ​​of the output voltage Vc of the operational amplifier U1 corresponding to four abnormal conditions.

[0046] In this embodiment, due to the particularity of the resistance value of the resistor network, the output voltage Vcnormal of the current information processing circuit 2 under normal working conditions is equal to the reference voltage V REF (ie 5V), the upper voltage limit V of the window comparison circuit can be adjusted based on the normal range of Vcnormal and the abnormal current that the circuit can tolerate. TH1 and the voltage lower limit V TH2 When Vccase1 to Vccase4 do not meet V TH2 <Vccase1、Vccase2、Vccase3、Vccase4<V TH1 When the window comparison circuit outputs a low level, an alarm is generated. The normal range of Vcnormal in this example is analyzed as follows: Ideally, Vcnormal in this implementation is always equal to the reference voltage V REF , which is independent of Iout and Vin. In actual circuits, considering the resistor accuracy, resistor value drift, and the non-ideality of the op amp, Vcnormal is proportional to V REFThere is an error. The inputs for error analysis are as follows: The maximum procurement error of resistors R5 and R6 is ±1%, the maximum drift error during the life cycle is ±2%, and the total maximum error is ±3%. Resistors R1, R2, R3, and R4 are 10K thin-film resistor arrays, with the model number ACASA1000S1000P1AT from VISHAY. Their relative accuracy during the life cycle is ±0.125%, and the absolute accuracy is ±0.25%. The maximum input offset voltage Vos of the operational amplifier LM2904A is ±4mV, and the error of the current sampling resistors Shunt1 and Shunt2 is ±1%, introducing a differential-mode signal V DTOL The error is ±2.5mV. Due to the resistor errors, the condition of R1 = R2 = R3 = R4 mentioned above is no longer satisfied, and the formula for Vcnormal is updated to:

[0047]

[0048] For error estimation, in the formula, R1, R2, R3, R4, R5, and R6 can be respectively denoted as R1 = 10k*(1 + tolr1), R2 = 10k*(1 + tolr2), R3 = 10k*(1 + tolr3), R4 = 10k*(1 + tolr4), R5 = 100k*(1 + tolr5), R6 = 100k*(1 + tolr6). Where: -0.25% < tolr1, tolr2, tolr3, tolr4 < 0.25%, -3% < tolr5, tolr6 < 3%. tolr1 to tolr6 are the deviations of the actual resistance values of resistors R1 to R6 relative to the nominal resistance values.

[0049] Vcnormal reaches the maximum value V REFMAX and the minimum value V REFMIN under the following conditions:

[0050]

[0051] Set the values of V TH1 and V TH2 : Assume that the abnormal current protection circuit can resist a minimum unbalanced current of 2 amperes, that is, when |I1 - I2| < 2A, the diagnostic signal will not be triggered. It can be set that V TH1 = V REFMAX + 2*A = 7.76V, V TH1 = V REFMIN - 2*A = 2.21V. The values of resistors R8, R9, and R10 can be adjusted to obtain the designed V TH1 and V TH2 voltages. When the drive circuit malfunctions and Vc > V TH1When Vc <V TH2 When , a second diagnostic signal Alarm2 is generated.

[0052] Second specific embodiment

[0053] Please refer to Fig.11 In this embodiment, the structure of the power driving circuit 100 is the same as that of the first embodiment.

[0054] The high-end current sampling circuit includes a current sampling resistor Shunt31, a resistor R31, a resistor R32, a resistor R33, a resistor R34, an operational amplifier U34 and an NPN transistor T1. The current input end and the current output end of the current sampling resistor Shunt31 are respectively connected to the positive electrode of the power supply Vin and the current inflow end A1 of the power driving circuit 100; one end of the resistor R31 is connected to the current input end P31 of the current sampling resistor Shunt31, and the other end of the resistor R31 is connected to the common connection point P34 of the in-phase input end of the operational amplifier U34 and the collector of the NPN transistor T1; one end of the resistor R32 is connected to the current output end P32 of the current sampling resistor Shunt31, and the other end of the resistor R32 is connected to the inverting input end of the operational amplifier U34; the base of the NPN transistor T1 is connected to the output end of the operational amplifier U34 through the resistor R33, the emitter of the NPN transistor T1 is connected to the negative electrode of the power supply Vin through the resistor R34, and the common connection point P35 of the emitter of the NPN transistor T1 and the resistor R34 outputs the first voltage signal V I1 .

[0055] The low-end current sampling circuit includes a current sampling resistor Shunt32, one end of the current sampling resistor Shunt32 is connected to the current outflow terminal A2 of the power driving circuit, the other end of the current sampling resistor Shunt32 is connected to the negative electrode of the power supply Vin, and one end of the current sampling resistor Shunt32 outputs a second voltage signal V I2 .

[0056] In this embodiment, current sampling resistors Shunt31 and Shunt32 are precision current sampling resistors with a resistance of 20mOhm. Resistors R31, R32, R33 and R34 are common resistors, with a resistance of 100Ohm and a resistance of 1Kohm. Operational amplifier U34 is a general voltage operational amplifier of TI, with a model of LM2904A, and NPN transistor T1 has a model of BC817.

[0057] When a positive current I1 flows through the current sampling resistor Shunt31, the output of the op amp U34 affects the voltage of the non-inverting input terminal through the circuit of resistor R33, resistor R31, NPN transistor T1, and resistor R34, forming a negative feedback. The op amp U34 will drive the base current of the NPN transistor T1 within the effective range of negative feedback, so that the net input voltage of the non-inverting and inverting input terminals of the op amp U34 is very close to 0V. Ignoring the current flowing into the non-inverting and inverting input terminals of the op amp U34 (because they are only at the level of tens of nA), the voltage drop across the resistor R32 is approximately 0V, and V P32 =V P34 , V Shunt31 =V R31 The collector current amplification factor of NPN transistor T1 is more than 200, and it can be approximately considered that the collector current is equal to the emitter current, that is, the current flowing through resistor R31 from the current input terminal P31 of current sampling resistor Shunt31 to the common point P34 of the in-phase input terminal of operational amplifier U34 and the collector of NPN transistor T1 is equal to the current flowing through resistor R34 from the common point P35 of the emitter of NPN transistor T1 and resistor R34 to the ground. The resistance values ​​of resistors R31 and R34 are equal, and the voltage drops across them are also equal, that is, V R34 =V R31 =V Shunt31 The circuit converts the voltage drop across the current sampling resistor Shunt31 to the resistor R34. The current I1 and current I2 signals are converted into a voltage signal V relative to the ground. P35 and V P33 , which is convenient for subsequent circuit processing.

[0058] The current information processing circuit is a differential amplifier circuit, which includes an operational amplifier U31, a resistor R35, a resistor R36, a resistor R37, a resistor R38 and a reference voltage source 22. The output voltage of the reference voltage source is V REF In the second embodiment, the output voltage V of the reference voltage source is REF is 2.5V, while the output voltage V of the reference voltage source in the first embodiment REF is 5V.

[0059] One end of the resistor R35 is connected to the common point P35 of the emitter of the NPN transistor T1 and the resistor R34, and the other end of the resistor R35 is connected to the common point of the non-inverting input terminal of the operational amplifier U31 and one end of the resistor R36, and the other end of the resistor R36 is connected to the positive electrode of the reference voltage source 22, and the negative electrode of the reference voltage source 22 is connected to the negative electrode of the power supply Vin. One end of the resistor R37 is connected to one end P33 of the current sampling resistor Shunt32, and the other end of the resistor R37 is connected to the common point of the inverting input terminal of the operational amplifier U31 and one end of the resistor R38, and the other end of the resistor R38 is connected to the output terminal of the operational amplifier U31; the output terminal of the operational amplifier U31 is connected to the input terminal of the comparison diagnosis circuit 3.

[0060] Resistors R35 and R37 are common resistors, both with a resistance of 3.3kohm. Resistors R36 and R38 are common resistors, both with a resistance of 100kohm. Reference voltage source 22 is a 2.5V voltage source. Operational amplifier U31 is a general-purpose voltage operational amplifier from TI, model LM2904A. The output of operational amplifier U31 is Vc=V REF +(V P35 -V P33 )*A CL , that is, Vc = V REF +(I1-I2)*20mohm*A CL , where A CL is the DC closed-loop gain of op amp U1, A CL =30.3.

[0061] The comparison diagnosis circuit 3 is a window comparison circuit, including voltage comparators U2, U3, resistors R39, R40, R41, R42 and R43. Voltage comparators U2 and U3 are TI voltage comparators, model LM2903. The output of voltage comparator U2 is pulled up to a 5V voltage source through resistor R42, and the output of voltage comparator U3 is pulled up to a 5V voltage source through resistor R43. VCC is a 5V voltage source, and resistors R39, R40 and R41 form a voltage divider resistor network. By adjusting the appropriate resistance values ​​of resistors R39, R40 and R41, a suitable voltage upper limit V can be obtained. TH1 and the voltage lower limit V TH2 . Voltage lower limit V TH2 Connected to the inverting input of the voltage comparator U3, the upper voltage limit V TH1 Connected to the non-inverting input terminal of the voltage comparator U2. The output terminal of the current information processing circuit 2 is connected to the inverting input terminal of the voltage comparator U2 and the non-inverting input terminal of the voltage comparator U3. The function of the window comparison circuit is: when Vc>V TH1 When Vc <V TH2When the second diagnostic signal Alarm2 is output, the first diagnostic signal Alarm1 and the second diagnostic signal Alarm2 are both low level signals.

[0062] Analyze the maximum and minimum variation range of Vcnormal under normal conditions. The sources of Vcnormal errors are: resistance error of current sampling resistors Shunt31 and Shunt32: ±1%; input offset voltage Vos of op amp U31 and op amp U34: ±4mV; absolute error of R31, R34, resistor R35, resistor R36, resistor R37, resistor R38: ±3%; error of unequal collector and emitter currents of NPN transistor T1; error caused by load effect of input resistance of differential amplifier circuit on input signal source is smaller than the above errors and is ignored in analysis.

[0063] Assume that the maximum range of current I1 and I2 is 10A.

[0064]

[0065]

[0066] Set V TH1 and V TH2 Value: Assuming that the abnormal current protection circuit can withstand at least 1 ampere of unbalanced current, that is, when |I1-I2|<1A, the first diagnostic signal Alarm1 and the second diagnostic signal Alarm2 will not be triggered, and V TH1 =V REFMAX +1*20m*A CL =4.17V, V TH1 =V REFMIN -2*20m*A CL =0.95V, the values ​​of resistors R39, R40, and R41 can be adjusted to obtain the designed V TH1 and V TH2 Voltage. When the power drive circuit is abnormal and Vc>V TH1 Output the first diagnostic signal Alarm1, Vc <V TH2 The second diagnostic signal Alarm2 is outputted when

[0067] In the first embodiment, the second voltage signal V I2 Reference ground, the first voltage signal V I1 It is superimposed on the power supply voltage, and the difference between the two voltages is collected by the current information processing circuit. The first voltage signal V I1In essence, it is a weak differential signal superimposed on a high common-mode voltage. For normal circuit function, the resistor network R1, R2, R3, and R4 in the first embodiment need to use high-precision resistors, otherwise the high common-mode voltage will affect the output voltage V through the error of the resistor network. C The circuit including the operational amplifier U34 and the NPN transistor T1 in the second embodiment is provided to improve this problem. I1 The signal becomes a reference ground signal, eliminating the interference of the common mode signal. Therefore, the second embodiment has a lower requirement on the resistance error than the first embodiment.

[0068] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A diagnostic circuit for a power drive circuit, the power drive circuit comprising a current inflow end, a current outflow end, a first output end and a second output end; the current inflow end and the current outflow end are respectively used to connect to the positive electrode and the negative electrode of a power supply, and the first output end and the second output end are respectively used to connect to the first end and the second end of a load; characterized in that: The diagnostic circuit comprises: The current sampling circuit is used to collect the current I1 flowing from the positive electrode of the power supply into the current inflow end of the power driving circuit, and output a first voltage signal V related to the current I1. I1 , and collecting the current I2 flowing from the current outflow end of the power driving circuit into the negative electrode of the power supply, and outputting a second voltage signal V related to the current I2 I2 ; A current information processing circuit, wherein the input end of the current information processing circuit is connected to the output end of the current sampling circuit, and is used to process the first voltage signal V I1 and the second voltage signal V I2 Processing, output voltage Vc, Vc = V REF +(I1-I2)*A,V REF is the reference voltage, A is the amplification factor; A comparison diagnostic circuit, the input end of which is connected to the output end of the current information processing circuit, for determining whether the voltage Vc is greater than a preset voltage upper limit V TH1 , and whether it is less than the preset voltage lower limit V TH2 , when Vc is greater than V TH1 The first diagnostic signal is generated when Vc is less than V TH2 A second diagnostic signal is generated.

2. The diagnostic circuit of the power driving circuit according to claim 1, characterized in that: The current sampling circuit includes a high-end current sampling circuit and a low-end current sampling circuit; The high-end current sampling circuit includes a current sampling resistor Shunt31, a resistor R31, a resistor R32, a resistor R33, a resistor R34, an operational amplifier U34 and an NPN transistor T1; the current input end and the current output end of the current sampling resistor Shunt31 are respectively connected to the positive electrode of the power supply and the current inflow end of the power driving circuit; one end of the resistor R31 is connected to the current input end of the current sampling resistor Shunt31, and the other end of the resistor R31 is connected to the common connection point of the in-phase input end of the operational amplifier U34 and the collector of the NPN transistor T1; one end of the resistor R32 is connected to the current output end of the current sampling resistor Shunt31, and the other end of the resistor R32 is connected to the inverting input end of the operational amplifier U34; the base of the NPN transistor T1 is connected to the output end of the operational amplifier U34 through the resistor R33, the emitter of the NPN transistor T1 is connected to the negative electrode of the power supply through the resistor R34, and the common connection point of the emitter of the NPN transistor T1 and the resistor R34 outputs a first voltage signal V I1 ; The low-end current sampling circuit includes a current sampling resistor Shunt32, one end of the current sampling resistor Shunt32 is connected to the current output end of the power driving circuit, the other end of the current sampling resistor Shunt32 is connected to the negative electrode of the power supply, and one end of the current sampling resistor Shunt32 outputs a second voltage signal V I2 .

3. The diagnostic circuit of the power driving circuit according to claim 2, characterized in that: The resistance values ​​of the resistor R31 and the resistor R34 are equal.

4. The diagnostic circuit of the power driving circuit according to claim 2, characterized in that: The current information processing circuit is a differential amplifier circuit, which includes an operational amplifier U31, a resistor R35, a resistor R36, a resistor R37, a resistor R38 and a reference voltage source. The output voltage of the reference voltage source is V REF ; One end of resistor R35 is connected to the common point of the emitter of NPN transistor T1 and resistor R34, the other end of resistor R35 is connected to the common point of the in-phase input terminal of operational amplifier U31 and one end of resistor R36, the other end of resistor R36 is connected to the positive electrode of the reference voltage source, and the negative electrode of the reference voltage source is connected to the negative electrode of the power supply; one end of resistor R37 is connected to one end of current sampling resistor Shunt32, the other end of resistor R37 is connected to the common point of the inverting input terminal of operational amplifier U31 and one end of resistor R38, the other end of resistor R38 is connected to the output terminal of operational amplifier U31; the output terminal of operational amplifier U31 is connected to the input terminal of the comparison diagnostic circuit.

5. The diagnostic circuit of the power driving circuit according to claim 1, characterized in that: The current sampling circuit includes a high-end current sampling circuit and a low-end current sampling circuit; The high-end current sampling circuit includes a current sampling resistor Shunt1, a current input end and a current output end of the current sampling resistor Shunt1 are respectively connected to the positive electrode of the power supply and the current inflow end of the power driving circuit, and a first voltage signal V is output from the current input end and the current output end of the current sampling resistor Shunt1. I1 ; The low-end current sampling circuit includes a current sampling resistor Shunt2, one end of the current sampling resistor Shunt2 is connected to the current outflow end of the power driving circuit, the other end of the current sampling resistor Shunt2 is connected to the negative electrode of the power supply, and one end of the current sampling resistor Shunt2 outputs a second voltage signal V I2 .

6. The diagnostic circuit of the power driving circuit according to claim 5, characterized in that: The current information processing circuit includes an operational amplifier U1, a resistor R5, a resistor R6, a resistor network and a reference voltage source. The output voltage of the reference voltage source is V REF , the resistor network includes a first series branch and a second series branch, the first series branch includes a resistor R1 and a resistor R2 connected in series with each other, and the second series branch includes a resistor R3 and a resistor R4 connected in series with each other; The two ends of the first series branch are respectively connected to the current input end of the current sampling resistor Shunt1 and the negative electrode of the power supply; the two ends of the second series branch are respectively connected to the current output end of the current sampling resistor Shunt1 and one end of the current sampling resistor Shunt2; the common point of the resistor R1 and the resistor R2 is connected to the common point of one end of the resistor R6 and the in-phase input end of the operational amplifier U1, and the common point of the resistor R3 and the resistor R4 is connected to the common point of one end of the resistor R5 and the inverting input end of the operational amplifier U1; the other end of the resistor R5 is connected to the output end of the operational amplifier U1, the other end of the resistor R6 is connected to the positive electrode of the reference voltage source, and the negative electrode of the reference voltage source is connected to the negative electrode of the power supply; the output end of the operational amplifier U1 is connected to the input end of the comparison diagnostic circuit.

7. The diagnostic circuit of the power driving circuit according to claim 6, characterized in that: The resistance values ​​of resistors R1, R2, R3 and R4 are 10 Kohm respectively; The resistance values ​​of the current sampling resistor Shunt1 and the current sampling resistor Shunt2 are 50mohm respectively.

8. The diagnostic circuit of the power drive circuit according to any one of claims 1 to 7, characterized in that: The comparison diagnosis circuit is a window comparison circuit.

9. The diagnostic circuit of the power driving circuit according to claim 1, characterized in that: The first diagnosis signal and the second diagnosis signal are level signals.

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