Drive circuit

Abstract

A bootstrap capacitor is connected between a high-side ground line connected to a connection point of a high-side switching element and a low-side switching element connected to a totem pole, and a high-side power supply line connected to a control power supply potential. A bootstrap diode is connected between the control power supply potential and the bootstrap capacitor. A high-side control circuit receives a high-side control signal and supplies a control signal to a high-side drive circuit. A detection circuit detects a voltage of the bootstrap capacitor. A power supply cutoff switch cuts off a power supply of the high-side control circuit when the voltage detected by the detection circuit becomes lower than a set value.

Description

Technical Field

[0001] This disclosure relates to a bootstrap driving circuit for driving semiconductor switching elements. Background Technology

[0002] Typically, in circuits such as inverters, the on / off control is performed on the two main circuit elements connected by a totem pole (specifically, the high-side switching element and the low-side switching element). Consideration is given to using N-channel (Nch) transistors in the low-side switching element and P-channel (Pch) transistors in the high-side switching element. However, Pch transistors are more expensive than Nch transistors. Therefore, to reduce costs, the use of Nch transistors in the high-side switching element is becoming increasingly common.

[0003] To drive an Nch transistor, a sufficient gate / source voltage is required. When the high-side Nch transistor is turned on, its source potential is approximately equal to the main supply voltage. Therefore, to drive the Nch transistor, a voltage higher than the main supply voltage needs to be generated. To generate a voltage higher than this main supply voltage, a bootstrap method is often used.

[0004] In the bootstrap mode, a bootstrap capacitor is connected between the source potential of the high-side Nch transistor and the control power supply potential. During the period when the high-side Nch transistor is off and the low-side Nch transistor is on, the control power supply charges the bootstrap capacitor. During the period when the high-side Nch transistor is on and the low-side Nch transistor is off, the charge in the bootstrap capacitor drives the high-side Nch transistor.

[0005] The voltage of the bootstrap capacitor gradually decreases due to the current consumed by the drive. If the voltage of the bootstrap capacitor drops significantly, the operation of the high-side control circuit becomes unstable, and the high-side control circuit incorrectly controls the high-side drive circuit, sometimes causing malfunctions in the high-side Nch transistor.

[0006] As a drive circuit to prevent malfunction when the voltage of the bootstrap capacitor drops significantly, Patent Document 1 discloses the following circuit structure: a switch is set on the signal output line of the high-side control circuit and the high-side drive circuit, and a Zener diode and a voltage divider resistor are used to open the switch when a voltage drop above a fixed value of the bootstrap capacitor is detected.

[0007] Patent Document 2 discloses a circuit structure for the purpose of suppressing the current consumption of the bootstrap diode: when the voltage drop of the bootstrap capacitor above a fixed value is detected by the resistor voltage divider and comparator, an "L" signal is output to the NAND circuit connected to the output line of the high-side drive circuit, so that the main circuit element on the high side is disconnected.

[0008] Prior art literature

[0009] Patent documents

[0010] Patent Document 1: Japanese Patent Application Publication No. 2005-168234

[0011] Patent Document 2: Japanese Patent Application Publication No. 2011-172309 Summary of the Invention

[0012] In the circuit structures disclosed in Patent Documents 1 and 2, if the potential on the lower side of the bootstrap capacitor fluctuates significantly when the main circuit element is switched on / off, the voltage detection signal of the bootstrap capacitor will be affected, which may also adversely affect the operation of the main circuit element. Depending on the situation, the main circuit element may be switched on / off repeatedly, resulting in malfunctions in the main circuit element. In addition, in the circuit load (16) disclosed in Patent Document 2, noise countermeasures are implemented, but the circuit structure becomes more complex.

[0013] A driving circuit according to one aspect of this disclosure includes: a bootstrap capacitor connected between a high-side ground line and a high-side power line, the high-side ground line being connected to the connection point of a high-side switching element and a low-side switching element connected by a totem pole at the connection point, the high-side power line being connected to a control power supply potential; a bootstrap diode connected in a positive direction from the control power supply potential to the bootstrap capacitor between the control power supply potential and the bootstrap capacitor; a high-side driving circuit that outputs a driving signal to the control terminal of the high-side switching element to control the on / off state of the high-side switching element; a high-side control circuit that receives a high-side control signal and supplies a control signal to the high-side driving circuit; a detection circuit that detects the voltage of the bootstrap capacitor; and a power cut-off switch that cuts off the power supply to the high-side control circuit if the voltage detected by the detection circuit is below a set value.

[0014] According to this disclosure, a stable bootstrap driving circuit can be implemented with a simple structure. Attached Figure Description

[0015] Figure 1 This is a diagram showing the circuit structure of the drive circuit for the bootstrap method involved in Embodiment 1.

[0016] Figure 2 This is a diagram showing the circuit structure of the drive circuit for the bootstrap method involved in Embodiment 2. Detailed Implementation

[0017] Figure 1This is a diagram illustrating the circuit structure of the drive circuit 10 according to Embodiment 1, which uses a bootstrap method. The drive circuit 10 in this embodiment drives a high-side switching element Q1 and a low-side switching element Q2 connected in series at connection point J1 like totem poles. In this embodiment, it is envisioned that N-channel MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) are used in both the high-side and low-side switching elements Q1 and Q2.

[0018] The drain terminal of the high-side switching element Q1 is connected to the main power supply potential HV (e.g., around 100V to 300V), and the source terminal of the low-side switching element Q2 is connected to ground. The source terminal of the high-side switching element Q1 and the drain terminal of the low-side switching element Q2 are connected at connection point J1, and the output line of the main circuit is connected to connection point J1. A load 20 is connected between the output line of the main circuit and the ground potential.

[0019] In this specification, the output voltage of the battery modules included in the battery pack is assumed to be the main power supply voltage. Therefore, a high-side switching element Q1 and a low-side switching element Q2 are connected between the positive and negative terminals of the battery modules. A heater for heating the battery modules is assumed to be the load 20. In battery packs designed for cold regions, a heater for heating the battery modules is typically provided to suppress battery cell degradation caused by low-temperature charging and discharging. The heater is, for example, a heating element with built-in heating wires, which is attached to the surface of the battery module.

[0020] The drive circuit 10 according to Embodiment 1 includes: a high-side control circuit 11, a high-side drive circuit 12, a low-side control circuit 13, a low-side drive circuit 14, a bootstrap capacitor Cb, a bootstrap diode Db, a detection circuit 15, a power cut-off switch Qs, and a pull-up resistor Ru.

[0021] The bootstrap capacitor Cb is connected between the high-side power line L1, which is connected to the control power supply potential VDD (e.g., around 12V to 15V), and the high-side ground line L2, which is connected to the connection point J1 between the high-side switching element Q1 and the low-side switching element Q2. The bootstrap diode Db is connected in the high-side power line L1, between the control power supply potential VDD and the bootstrap capacitor Cb, in a forward direction from the control power supply potential VDD to the bootstrap capacitor Cb.

[0022] The high-side drive circuit 12 outputs a drive signal to the gate terminal of the high-side switching element Q1 to control the on / off state of the high-side switching element Q1. The positive power supply terminal of the high-side drive circuit 12 is connected to the high-side power supply line L1, and the negative power supply terminal is connected to the high-side ground line L2.

[0023] The high-side drive circuit 12 can, for example, be constructed from a high-side transistor and a low-side transistor connected by a totem pole. An NPN transistor can be used in the high-side transistor, and a PNP transistor in the low-side transistor. Alternatively, a Pch (P-channel) MOSFET can be used in the high-side transistor, and an Nch MOSFET in the low-side transistor. In this case, the control signal input to the high-side drive circuit 12 and the drive signal output from the high-side drive circuit 12 are logically inverted. To ensure that the control signal input to the high-side drive circuit 12 is logically consistent with the drive signal output from the high-side drive circuit 12, an inversion circuit needs to be provided before the gate terminals of the Pch MOSFET and the Nch MOSFET.

[0024] The high-side control circuit 11 receives the high-side control signal from the front-end microcontroller 100 and supplies the control signal to the high-side drive circuit 12 via the signal output line L3. The high-side control signal is defined by a binary signal consisting of a high-level signal and a low-level signal. The voltage of the high-level signal is set to approximately 3V to 5V. The voltage of the low-level signal is essentially set to 0V. The positive power supply terminal of the high-side control circuit 11 is connected to the high-side power supply line L1, and the negative power supply terminal is connected to the high-side ground line L2.

[0025] The high-side control circuit 11 isolates the preceding microcontroller 100 from the subsequent high-side drive circuit 12 and shifts the high-side control signal level from the microcontroller 100. The high-side control circuit 11 can, for example, be constructed using an optocoupler IC. The optocoupler IC includes a light-emitting diode (LED) and a phototransistor. The LED is connected to the input line from the microcontroller 100 that receives the high-side control signal. The phototransistor and a resistor are connected in series between the high-side power line L1 and the high-side ground line L2. The connection point between the phototransistor and the resistor is connected to the signal output line L3. The phototransistor is switched on / off depending on whether the LED is emitting light.

[0026] The low-side drive circuit 14 outputs a drive signal to the gate terminal of the low-side switching element Q2 to control the on / off state of the low-side switching element Q2. The positive power supply terminal of the low-side drive circuit 14 is connected to the low-side power supply line connected to the control power supply potential VDD, and the negative power supply terminal is connected to the low-side ground line connected to the source terminal of the low-side switching element Q2. The low-side drive circuit 14, like the high-side drive circuit 12, can also be constructed, for example, by a totem-pole connected high-side transistor and a low-side transistor.

[0027] The low-side control circuit 13 receives low-side control signals from the preceding microcontroller 100 and supplies control signals to the low-side drive circuit 14 via the signal output line. The low-side control signal, excluding the dead time of the high-side switching element Q1 and the low-side switching element Q2, is a complementary signal to the high-side control signal. The positive power supply terminal of the low-side control circuit 13 is connected to the low-side power supply line, and the negative power supply terminal is connected to the low-side ground line.

[0028] The low-side control circuit 13 isolates the preceding microcontroller 100 from the subsequent low-side drive circuit 14 and shifts the low-side control signal level from the microcontroller 100. The low-side control circuit 13, like the high-side control circuit 11, can also be constructed, for example, by an optocoupler IC. Furthermore, insulation is not necessary when the source potential of the low-side switching element Q2 is the same as the ground potential of the microcontroller 100's ground 100G.

[0029] During the period when the high-side control signal is low and the low-side control signal is high, the high-side switching element Q1 is controlled to be open, and the low-side switching element Q2 is controlled to be closed, and the bootstrap capacitor Cb is charged from the control power supply potential VDD. The potential on the lower side of the bootstrap capacitor Cb is fixed at the ground potential, and the potential on the upper side of the bootstrap capacitor Cb rises to (control power supply potential VDD - forward voltage Vf of bootstrap diode Db) (hereinafter referred to as the charging voltage).

[0030] During the period when the high-side control signal is high and the low-side control signal is low, the high-side switching element Q1 is controlled to be turned on, and the low-side switching element Q2 is controlled to be turned off. The potential on the lower side of the bootstrap capacitor Cb rises to the main power supply potential HV. The potential on the upper side of the bootstrap capacitor Cb rises to (main power supply potential HV + charging voltage). That is, the gate potential of the high-side switching element Q1 is higher than the source potential by an amount equivalent to the charging voltage of the bootstrap capacitor Cb, and the high-side switching element Q1 is turned on. If the voltage charging the bootstrap capacitor Cb is lower than the threshold voltage Vt of the high-side switching element Q1, then the high-side switching element Q1 is turned off.

[0031] The detection circuit 15 detects the voltage of the bootstrap capacitor Cb. In this embodiment, the detection circuit 15 is composed of a resistor voltage divider circuit (a series circuit of the first resistor R1 and the second resistor R2) connected to the two ends of the bootstrap capacitor Cb. Alternatively, the detection circuit 15 may also be constructed using a Zener diode.

[0032] A power cut-off switch Qs is connected between the negative power terminal of the high-side control circuit 11 and the high-side ground line L2. When the voltage detected by the detection circuit 15 is higher than a set value, the power cut-off switch Qs supplies power to the high-side control circuit 11. When the voltage detected by the detection circuit 15 is lower than the set value, the power cut-off switch Qs cuts off the power to the high-side control circuit 11. In this embodiment, an Nch-MOSFET is used in the power cut-off switch Qs.

[0033] The voltage division ratio of the resistor divider circuit of the detection circuit 15 is set such that if it drops to the voltage of the bootstrap capacitor Cb (which should turn off the high-side switching element Q1) (a voltage slightly higher than the threshold voltage Vt of the high-side switching element Q1), it is lower than the threshold voltage Vt of the power cut-off switch Qs (Nch-MOSFET).

[0034] During normal operation, when the high-side control signal is high and the low-side control signal is low, the voltage obtained by dividing the voltage of the bootstrap capacitor Cb using a resistor divider circuit (hereinafter referred to as the detection voltage) is sufficient to maintain the power cut-off switch Qs in the ON state. Even if the potential on the lower side of the bootstrap capacitor Cb changes significantly during the period when the high-side control signal is high and the low-side control signal is low, the potential on the upper side of the bootstrap capacitor Cb changes accordingly, thus stably maintaining the power cut-off switch Qs in the ON state.

[0035] During normal operation, when the high-side control signal is low and the low-side control signal is high, the detected voltage is consistently lower than the threshold voltage Vt of the power cut-off switch Qs, thus ensuring that the power cut-off switch Qs remains stably open.

[0036] A pull-up resistor Ru is connected between the high-side power supply line L1 and the signal output line L3 of the high-side control circuit 11. If the detected voltage decreases, the power cut-off switch Qs turns off, and the power supply to the high-side control circuit 11 is cut off, thus disconnecting the output of the high-side control circuit 11. When the output of the high-side control circuit 11 is disconnected, the signal output line L3 is pulled up to the potential of the high-side power supply line L1 via the high-resistance pull-up resistor Ru. Therefore, even if the potential at the lower end of the bootstrap capacitor Cb changes significantly, it will not directly affect the potential of the signal output line L3.

[0037] As explained above, according to Embodiment 1, when the potential of the high-side grounding line L2 fluctuates significantly due to the switching on / off of the high-side switching element Q1 and the low-side switching element Q2, the power supply to the high-side control circuit 11 is cut off, and the output of the high-side control circuit 11 is disabled. Therefore, through the output of the high-side control circuit 11, the potential of the signal output line L3 does not fluctuate, the high-side drive circuit 12 can stably and continuously perform a disconnect output, and the high-side switching element Q1 can be stably maintained in an open state.

[0038] If the high-side switching element Q1 and the low-side switching element Q2 are repeatedly switched on and off with large currents, the SOA (Safety Operation Area) may be damaged due to heat generation. To prevent this, when the voltage of the bootstrap capacitor Cb drops significantly to near the threshold voltage Vt of the high-side switching element Q1, the high-side switching element Q1 needs to be momentarily turned off, and then the gate voltage is fixed at the off position to prevent the gate voltage of the high-side switching element Q1 from fluctuating. In this regard, according to Embodiment 1, after the voltage of the bootstrap capacitor Cb falls below the threshold voltage Vt of the high-side switching element Q1, the gate voltage of the high-side switching element Q1 can be stably fixed at the off position.

[0039] In Embodiment 1, a circuit for stabilizing the gate voltage can be constructed using a relatively small number of components, including a first resistor R1, a second resistor R2, a power-off switch Qs (Nch-MOSFET), and a pull-up resistor Ru. Therefore, according to Embodiment 1, a stable bootstrap drive circuit 10 can be implemented with a simple structure.

[0040] Figure 2 This is a diagram showing the circuit structure of the drive circuit 10 in the bootstrap mode according to Embodiment 2. In Embodiment 2, in Figure 1 In the driving circuit 10 of the embodiment 1 shown, a charging cut-off switch SW1 and a reversing circuit 16 are added.

[0041] The charging cut-off switch SW1 is connected in the high-side power line L1 between the control power supply potential VDD and the bootstrap diode Db. The charging cut-off switch SW1 is controlled to be open during the period when the high-side control signal is high. In this embodiment, a Pch-MOSFET is used in the charging cut-off switch SW1. The inverting circuit 16 inverts the logic of the high-side control signal and outputs it to the gate terminal of the Pch-MOSFET. Alternatively, if the charging cut-off switch SW1 uses a switch that is open during the period when the high-side control signal is high, the inverting circuit 16 is not required.

[0042] In embodiment 2, even if the voltage of the bootstrap capacitor Cb decreases and the potential on the upper side of the bootstrap capacitor Cb is lower than the control power supply potential VDD, the bootstrap capacitor Cb will not recharge because the charging cut-off switch SW1 is open during the period when the high-side control signal is high. Therefore, malfunctions of the high-side control circuit 11 and the high-side drive circuit 12 are prevented, and repeated switching of the high-side switching element Q1 can be prevented from damaging it.

[0043] Implementation method 2 is suitable for applications where the switching speed of the main circuit elements is slow. When the switching speed of the high-side switching element Q1 and the low-side switching element Q2 is slow, during the period when the high-side control signal is at a high level, it is easy for the potential on the upper side of the bootstrap capacitor Cb to be lower than the control power supply potential VDD.

[0044] On the other hand, when the switching speed of the main circuit components is fast, it is difficult for the potential on the upper side of the bootstrap capacitor Cb to fall below the control power supply potential VDD during the period when the high-side control signal is high. Therefore, in applications where the switching speed of the main circuit components is fast, the circuit structure of Embodiment 1 can be adopted. Furthermore, in applications where the switching speed of the main circuit components is fast, if the circuit structure of Embodiment 2 is also adopted, it has the effect of reducing the capacitance of the bootstrap capacitor Cb.

[0045] As described above, when the load 20 is a heater, there is less need to switch the main circuit elements at high speed. Therefore, the circuit structure of Embodiment 2 can also be used to switch the main circuit elements in seconds.

[0046] The present disclosure has been described above based on the embodiments. The embodiments are illustrative, and those skilled in the art will understand that various modifications can be made to the combination of these structural elements and processing procedures, and such modifications are also within the scope of the present disclosure.

[0047] In embodiments 1 and 2 described above, an example of using an Nch-MOSFET in the high-side switching element Q1 and the low-side switching element Q2 is given. In this respect, an NPN bipolar transistor can also be used in the high-side switching element Q1 and the low-side switching element Q2. In this case, "gate," "source," and "drain" are replaced with "base," "emitter," and "collector," respectively. Alternatively, an IGBT (Insulated Gate Bipolar Transistor) can also be used in the high-side switching element Q1 and the low-side switching element Q2. In this case, "gate," "source," and "drain" are replaced with "gate," "emitter," and "collector," respectively.

[0048] In embodiments 1 and 2 described above, an example was given in which a power cut-off switch Qs was connected between the negative power supply terminal of the high-side control circuit 11 and the high-side ground line L2. In this respect, a power cut-off switch Qs can also be connected between the high-side power supply line L1 and the positive power supply terminal of the high-side control circuit 11. In this case, instead of a pull-up resistor Ru, a pull-down resistor is connected between the signal output line L3 of the high-side control circuit 11 and the high-side ground line L2.

[0049] In this way, when the power cut-off switch Qs is connected to the lower side of the high-side control circuit 11, a pull-up resistor Ru is connected to the signal output line L3; when the power cut-off switch Qs is connected to the upper side of the high-side control circuit 11, a pull-down resistor is connected to the signal output line L3. This eliminates the noise effect when the power cut-off switch Qs is turned off.

[0050] Alternatively, the implementation method can also be determined by the following items.

[0051] [Project 1]

[0052] A driving circuit (10) comprising:

[0053] A bootstrap capacitor (Cb) is connected between a high-side ground wire (L2) and a high-side power supply wire (L1). The high-side ground wire (L2) is connected to the connection point (J1) of a high-side switching element (Q1) and a low-side switching element (Q2) connected by a totem pole at the connection point (J1). The high-side power supply wire (L1) is connected to the control power supply potential (VDD).

[0054] A bootstrap diode (Db) is positively connected between the control power supply potential (VDD) and the bootstrap capacitor (Cb) in the direction from the control power supply potential (VDD) to the bootstrap capacitor (Cb).

[0055] The high-side drive circuit (12) outputs a drive signal to the control terminal of the high-side switch element (Q1) to control the on / off state of the high-side switch element (Q1);

[0056] The high-side control circuit (11) receives the high-side control signal and supplies the control signal to the high-side drive circuit (12);

[0057] The detection circuit (15) detects the voltage of the bootstrap capacitor (Cb); and

[0058] If the voltage detected by the detection circuit (15) is below a set value, the power supply to the high-side control circuit (11) is cut off by the power cut-off switch (Qs).

[0059] Thus, a stable bootstrap driving circuit (10) can be realized with a simple structure.

[0060] [Project 2]

[0061] In the driving circuit (10) described in Project 1,

[0062] The high-side control circuit (11) is connected between the high-side power line (L1) and the high-side ground line (L2), and performs level shifting on the high-side control signal and supplies it to the high-side drive circuit (12).

[0063] The power cut-off switch (Qs) is connected between the negative power terminal of the high-side control circuit (11) and the high-side grounding wire (L2).

[0064] A pull-up resistor (Ru) is connected between the signal output line (L3) between the high-side control circuit (11) and the high-side drive circuit (12) and the high-side power supply line (L1).

[0065] This prevents the drive signal of the high-side switching element Q1 from fluctuating when the voltage of the bootstrap capacitor Cb decreases.

[0066] [Project 3]

[0067] In the driving circuit (10) described in Project 1 or 2,

[0068] It also includes: a charging cut-off switch (SW1) connected between the control power supply potential (VDD) and the bootstrap diode (Db).

[0069] The charging cut-off switch (SW1) is disconnected during the period when the high-side control signal is high.

[0070] This prevents repeated charging and discharging of the bootstrap capacitor (Cb) during periods when the high-side control signal is at a high level.

[0071] -Symbol Explanation-

[0072] 10. Drive Circuit

[0073] 11 High-side control circuit

[0074] 12 High-side drive circuit

[0075] 13 Low-side control circuit

[0076] 14 Low-side drive circuit

[0077] 15 Detection Circuit

[0078] 16 Reverse Circuit

[0079] 20 load

[0080] Q1 High-side switching element

[0081] Q2 Low-side switching element

[0082] Cb bootstrap capacitor

[0083] Db bootstrap diode

[0084] Qs power cut-off switch

[0085] SW1 Charging cut-off switch

[0086] R1 is the first resistor.

[0087] R2 is the second resistor.

[0088] Ru is a pull-up resistor.

Claims

1. A driving circuit, comprising: A bootstrap capacitor is connected between a high-side ground wire and a high-side power supply wire. The high-side ground wire is connected to the connection point of a high-side switching element and a low-side switching element connected by a totem pole at the connection point. The high-side power supply wire is connected to the control power supply potential. A bootstrap diode is connected in the positive direction from the control power supply potential to the bootstrap capacitor between the control power supply potential and the bootstrap capacitor; The high-side drive circuit outputs a drive signal to the control terminal of the high-side switching element to control the on / off state of the high-side switching element; The high-side control circuit receives the high-side control signal and supplies the control signal to the high-side drive circuit. A detection circuit detects the voltage of the bootstrap capacitor; as well as If the voltage detected by the detection circuit falls below a set value, the power supply to the high-side control circuit is cut off by the power cut-off switch.

2. The driving circuit according to claim 1, wherein, The high-side control circuit is connected between the high-side power line and the high-side ground line, performs level shifting on the high-side control signal, and supplies it to the high-side drive circuit. The power cut-off switch is connected between the negative power terminal of the high-side control circuit and the high-side grounding wire. A pull-up resistor is connected between the signal output line and the high-side power supply line between the high-side control circuit and the high-side drive circuit.

3. The driving circuit according to claim 1 or 2, wherein, It also includes: a charging cut-off switch connected between the control power supply potential and the bootstrap diode. The charging cut-off switch is open during the period when the high-side control signal is at a high level.

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