Drive circuit

Abstract

In a bootstrap-type drive circuit 10, a voltage holding capacitor Ch has a high-potential-side terminal connected to a high-side power supply line L1 and a low-potential-side terminal connected to a high-side ground line L2. A first control switch SW1 is connected between a low-potential-side terminal of a first bootstrap capacitor Cb1 and the low-potential-side terminal of the voltage holding capacitor Ch. A high-potential-side terminal of a second bootstrap capacitor Cb2 is connected to a node N1 between the first bootstrap capacitor Cb1 and the first control switch SW1. A second control switch SW2 is connected between a low-potential-side terminal of the second bootstrap capacitor Cb2 and a low-side ground line L3.

Description

Drive Circuit

[0001] The present disclosure relates to a bootstrap drive circuit for driving a semiconductor switching element.

[0002] Generally, in a circuit such as an inverter, two main circuit elements connected in a totem-pole configuration (specifically, a high-side switching element and a low-side switching element) are controlled to be turned on / off. It is conceivable to use an Nch transistor for the low-side switching element and a Pch transistor for the high-side switching element. However, since the Pch transistor is more expensive than the Nch transistor, due to the demand for cost reduction, the use of an Nch transistor for the high-side switching element is increasing.

[0003] A sufficient gate-source voltage is required to drive the Nch transistor. When the high-side Nch transistor is on and the low-side Nch transistor is off, the source potential of the high-side Nch transistor becomes approximately equal to the main power supply voltage applied to the drain terminal. Therefore, in order to drive the high-side Nch transistor, it is necessary to generate a voltage higher than the main power supply voltage (generally, about the main power supply voltage + 10V). The bootstrap method is often adopted to generate this voltage higher than the main power supply voltage.

[0004] In the bootstrap method, 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 bootstrap capacitor is charged with about 10V from the control power supply. During the period when the high-side Nch transistor is on and the low-side Nch transistor is off, the high-side Nch transistor is driven with the voltage of about 10V charged in the bootstrap capacitor.

[0005] In this bootstrap method, the high-side N-channel transistor and the low-side N-channel transistor are controlled by mutually exclusive switching. Since the control frequency of circuits such as inverters is typically in the range of several tens of kHz to 1 MHz, the capacitance of the bootstrap capacitor is around a few microseconds, and the on-time is less than milliseconds.

[0006] Bootstrap circuits can be implemented in a small area and generate the high voltage needed to drive a high-side N-channel transistor. However, in typical applications of bootstrap circuits, it is not possible to keep the high-side N-channel transistor constantly on. Increasing the capacitance of the bootstrap capacitor can extend the on-time, but it does not allow the transistor to be kept constantly on.

[0007] One option is to generate the high voltage for driving using an isolated DC / DC converter instead of a bootstrap circuit, but this would lead to increased mounting area, cost, and current consumption. Alternatively, it is possible to generate the high voltage for driving using a general charge pump control, but this requires operation within the voltage rating of the control IC, making it difficult to apply to applications where the main power supply voltage is 100V or higher.

[0008] Therefore, a method can be considered in which a high voltage for driving is generated by charge pump control based on the configuration of a bootstrap circuit (see, for example, Figure 1 of Patent Document 1 and Figure 2 of this specification). In this method, a changeover switch (corresponding to the first control switch SW1 and the second control switch SW2 in Figure 2) that can switch the low-potential terminal of the bootstrap capacitor between the source potential of the high-side Nch transistor and the source potential of the low-side Nch transistor is added, as well as a capacitor for maintaining the high voltage (corresponding to the voltage-holding capacitor Ch in Figure 2).

[0009] When the high-side N-channel transistor is permanently on and the low-side N-channel transistor is permanently off, the selector switch is switched to the source potential side of the low-side N-channel transistor to charge the bootstrap capacitor, and then the selector switch is switched to the source potential side of the high-side N-channel transistor to transfer the charge stored in the bootstrap capacitor to a capacitor for maintaining high voltage. This charge pump control allows for the stable generation of the high voltage required to drive the high-side N-channel transistor, even when the low-side N-channel transistor is off.

[0010] In this circuit configuration, since the selector switch is connected to the source potential of the high-side N-channel transistor, if the main power supply voltage exceeds 100V, the selector switch needs to be made to a high-voltage specification to compensate for its vulnerability to short-circuit failures. Furthermore, while it is assumed that a pair of MOSFETs (Metal-Oxide-Semiconductor Field-Effect Transistors) will be used for the selector switch, if the control of the pair of MOSFETs becomes unstable, they may simultaneously turn on, causing a large through-current and potentially leading to failure. To prevent simultaneous on-out, reliable mutual exclusion control using a high-spec control IC is necessary. Additionally, leakage current may flow from the main power supply through the selector switch at timings such as before circuit startup.

[0011] Japanese Utility Model Publication No. 5-41397

[0012] This disclosure is made in light of these circumstances, and its purpose is to provide a low-cost, highly safe, and versatile bootstrap drive circuit.

[0013] To solve the above problems, a drive circuit in one aspect of the present disclosure includes a first bootstrap capacitor connected between a high-side ground line connected to the connection point of totem-pole connected high-side switching elements and low-side switching elements, and a high-side power supply line connected to the control power supply potential, wherein the high-potential side terminal is connected to the high-side power supply line and the low-potential side terminal is connected to the high-side ground line; a bootstrap diode connected between the control power supply potential and the high-potential side terminal of the first bootstrap capacitor in the forward direction from the control power supply potential towards the first bootstrap capacitor; and a drive circuit connected between the high-side power supply line and the high-side ground line that outputs a drive signal corresponding to the high-side control signal to the control terminal of the high-side switching element, thereby driving the high-side switch The system includes a high-side drive circuit for controlling the on / off state of a switching element; a voltage-holding capacitor with its high-potential terminal connected to the high-side power line and its low-potential terminal connected to the high-side ground line; a voltage-holding diode connected in the forward direction from the first bootstrap capacitor to the voltage-holding capacitor between the high-potential terminal of the first bootstrap capacitor and the high-potential terminal of the voltage-holding capacitor; a first control switch connected between the low-potential terminal of the first bootstrap capacitor and the low-potential terminal of the voltage-holding capacitor; a second bootstrap capacitor with its high-potential terminal connected to the connection point between the first bootstrap capacitor and the first control switch; and a second control switch connected between the low-potential terminal of the second bootstrap capacitor and the low-side ground line.

[0014] According to this disclosure, a low-cost, highly safe, and versatile bootstrap-type drive circuit can be realized.

[0015] This figure shows the basic circuit configuration of a bootstrap drive circuit. This figure shows the circuit configuration of a bootstrap drive circuit according to a comparative example. This figure shows the circuit configuration of a bootstrap drive circuit according to an embodiment.

[0016] Figure 1 shows the basic circuit configuration of a bootstrap-type drive circuit 10. The bootstrap-type drive circuit 10 is a circuit that drives a totem-pole connected high-side switching element Q1 and low-side switching element Q2. In this specification, an example is assumed in which Nch-MOSFETs are used for the high-side switching element Q1 and low-side switching element Q2.

[0017] The drain terminal of the high-side switching element Q1 is connected to the main power supply potential HV (for example, about 100V to 300V), and the source terminal of the low-side switching element Q2 is connected to the ground potential. The source terminal of the high-side switching element Q1 and the drain terminal of the low-side switching element Q2 are connected, and the output line of the main circuit is connected to this connection point. A load 20 is connected between the output line of the main circuit and the ground potential.

[0018] In this specification, the output voltage of the battery module included in the battery pack is assumed to be the main power supply voltage. Therefore, the high-side switching element Q1 and the low-side switching element Q2 are assumed to be connected between the positive and negative terminals of the battery module. A heater for heating the battery module is assumed to be the load 20. In battery packs designed for cold climates, it is common to install a heater for heating the battery module in order to suppress cell degradation due to low-temperature charging and low-temperature discharging. The heater consists of, for example, a heating sheet with a built-in heating element, and the heating sheet is attached to the surface of the battery module.

[0019] The bootstrap drive circuit 10 includes a high-side drive circuit 11, a low-side drive circuit 12, a bootstrap capacitor Cb, and a bootstrap diode Db.

[0020] The high-potential terminal of the bootstrap capacitor Cb is connected to the high-side power line L1, which is connected to the control power supply potential VDD (for example, about 12V to 15V). The low-potential terminal of the bootstrap capacitor Cb is connected to the high-side ground line L2, which is connected to the connection point 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 the forward direction from the control power supply potential VDD towards the bootstrap capacitor Cb.

[0021] The high-side drive circuit 11 outputs a drive signal corresponding to the high-side control signal received from an external microcontroller (not shown) to the gate terminal of the high-side switching element Q1, thereby controlling the on / off state of the high-side switching element Q1. The positive power supply terminal of the high-side drive 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.

[0022] The high-side drive circuit 11 may be composed of, for example, a totem-pole connected high-side transistor and a low-side transistor. An NPN transistor may be used for the high-side transistor and a PNP transistor for the low-side transistor. Alternatively, a P-channel MOSFET may be used for the high-side transistor and an N-channel MOSFET for the low-side transistor. In this case, the logic of the control signal input to the high-side drive circuit 11 and the drive signal output from the high-side drive circuit 11 are inverted. In order to match the logic of the control signal input to the high-side drive circuit 11 and the drive signal output from the high-side drive circuit 11, it is necessary to provide an inverting circuit before the gate terminals of the P-channel MOSFET and the gate terminals of the N-channel MOSFET.

[0023] The low-side drive circuit 12 outputs a drive signal corresponding to the low-side control signal received from an external microcontroller to the gate terminal of the low-side switching element Q2, thereby controlling the on / off state of the low-side switching element Q2. The positive power supply terminal of the low-side drive circuit 12 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 L3 connected to the source terminal of the low-side switching element Q2. The low-side drive circuit 12, like the high-side drive circuit 11, can be configured, for example, with a totem-pole connected high-side transistor and a low-side transistor.

[0024] The high-side control signal and the low-side control signal are complementary signals, excluding the dead time of the high-side switching element Q1 and the low-side switching element Q2.

[0025] 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 off and the low-side switching element Q2 is controlled to be on, and the bootstrap capacitor Cb is charged from the control power supply potential VDD. The potential of the low-potential terminal of the bootstrap capacitor Cb is fixed at ground potential, and the potential of the high-potential terminal 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).

[0026] During the period when the high-side control signal is at a high level and the low-side control signal is at a low level, the high-side switching element Q1 is controlled to be on and the low-side switching element Q2 is controlled to be off. The potential of the low-potential terminal of the bootstrap capacitor Cb rises to the main power supply potential HV. The potential of the high-potential terminal 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 becomes higher than the source potential by the charging voltage of the bootstrap capacitor Cb, and the high-side switching element Q1 turns on. When the voltage charged in the bootstrap capacitor Cb falls below the threshold voltage of the high-side switching element Q1, the high-side switching element Q1 turns off.

[0027] Figure 2 shows the circuit configuration of a bootstrap drive circuit 10 according to a comparative example. The bootstrap drive circuit 10 according to the comparative example further includes a voltage holding capacitor Ch, a voltage holding diode Dh, a first control switch SW1, a second control switch SW2, and a control circuit 13, in addition to the basic configuration of the bootstrap drive circuit 10 shown in Figure 1.

[0028] The high-potential terminal of the voltage-holding capacitor Ch is connected to the high-side power supply line L1, and the low-potential terminal of the voltage-holding capacitor Ch is connected to the high-side ground line L2. The voltage-holding capacitor Ch is connected in parallel to the high-side drive circuit 11 and holds the high-voltage power supply voltage supplied to the high-side drive circuit 11.

[0029] The voltage-holding diode Dh is connected in the high-side power supply line L1 between the high-potential terminal of the bootstrap capacitor Cb and the high-potential terminal of the voltage-holding capacitor Ch, in the forward direction from the bootstrap capacitor Cb to the voltage-holding capacitor Ch.

[0030] The first control switch SW1 is connected to the high-side ground line L2 between the low-potential terminal of the bootstrap capacitor Cb and the low-potential terminal of the voltage-holding capacitor Ch. The second control switch SW2 is connected between the connection point N1 between the bootstrap capacitor Cb and the first control switch SW1 and the low-side ground line L3. N-channel MOSFETs can be used for both the first control switch SW1 and the second control switch SW2. Alternatively, a P-channel MOSFET may be used for the first control switch SW1. Furthermore, bipolar transistors or relays may be used for both the first control switch SW1 and the second control switch SW2.

[0031] The control circuit 13 controls the on / off state of the first control switch SW1 and the second control switch SW2. When the high-side switching element Q1 and the low-side switching element Q2 operate in a complementary manner, the control circuit 13 enables normal bootstrap control by fixing the first control switch SW1 to ON and the second control switch SW2 to OFF.

[0032] The control circuit 13 controls the charge pump by alternately switching the first control switch SW1 and the second control switch SW2 on and off when controlling the high-side switching element Q1 to be always on and the low-side switching element Q2 to be always off. Specifically, the control circuit 13 charges the bootstrap capacitor Cb from the control power supply potential VDD by controlling the first control switch SW1 to be off and the second control switch SW2 to be on. Next, the control circuit 13 transfers the charge stored in the bootstrap capacitor Cb to the voltage holding capacitor Ch by controlling the first control switch SW1 to be on and the second control switch SW2 to be off. As a result, even when the low-side switching element Q2 is always off, the voltage of the voltage holding capacitor Ch can be maintained at (main power supply potential HV + charging voltage - forward voltage Vf of the voltage holding diode Dh).

[0033] However, as mentioned above, when the main power supply potential HV is high voltage, the first control switch SW1 and the second control switch SW2 need to be high-voltage specifications to cover their vulnerability to short-circuit failures. In addition, reliable mutual exclusion control using a high-spec control circuit 13 is necessary to prevent failure caused by a large through-current flowing when the first control switch SW1 and the second control switch SW2 are turned on simultaneously. Furthermore, there is a possibility that leakage current may flow from the main power supply potential HV through the first control switch SW1 and the second control switch SW2 at timings such as before circuit startup. The following describes a bootstrap-type drive circuit 10 that solves these problems.

[0034] Figure 3 shows the circuit configuration of the bootstrap drive circuit 10 according to the embodiment. The bootstrap drive circuit 10 according to the embodiment further includes a second bootstrap capacitor Cb2 in addition to the configuration of the bootstrap drive circuit 10 according to the comparative example shown in Figure 2. Hereinafter, the bootstrap capacitor Cb in Figure 2 shall be read as the first bootstrap capacitor Cb1.

[0035] The high-potential terminal of the second bootstrap capacitor Cb2 is connected to the connection point N1 between the first bootstrap capacitor Cb1 and the first control switch SW1, and the low-potential terminal of the second bootstrap capacitor Cb2 is connected to the second control switch SW2. In other words, in the bootstrap drive circuit 10 according to this embodiment, the second bootstrap capacitor Cb2 is interposed between the first control switch SW1 and the second control switch SW2. Furthermore, when the first control switch SW1 is off and the second control switch SW2 is on, the first bootstrap capacitor Cb1 and the second bootstrap capacitor Cb2 are connected in series.

[0036] The capacitance ratio of the first bootstrap capacitor Cb1 and the second bootstrap capacitor Cb2 is set according to the value of the control power supply potential VDD. Since the drive voltage of a typical N-channel MOSFET is preferably around 8-13V, it is desirable to set the capacitance ratio of the first bootstrap capacitor Cb1 and the second bootstrap capacitor Cb2 so that the voltage charged to the first bootstrap capacitor Cb1 is approximately 8-13V.

[0037] For example, if the control power supply potential VDD is 12V, the capacitance ratio of the first bootstrap capacitor Cb1 and the second bootstrap capacitor Cb2 may be set to, for example, 1:10. In this case, the voltage charged to the first bootstrap capacitor Cb1 will be 10.9V (≈ 12V × 10 / 11).

[0038] Furthermore, if the control power supply potential VDD is 15V, the capacitance ratio of the first bootstrap capacitor Cb1 and the second bootstrap capacitor Cb2 may be set to, for example, 1:6. In this case, the voltage charged to the first bootstrap capacitor Cb1 will be 12.86V (≈ 15V × 6 / 7).

[0039] As described above, according to this embodiment, by providing a first control switch SW1 and a second control switch SW2 and operating the first control switch SW1 and the second control switch SW2 complementaryly, it is possible to control the high-side switching element Q1 to be permanently on. Alternatively, by controlling the first control switch SW1 to be permanently on and the second control switch SW2 to be permanently off, it is also possible to operate it in the same way as a normal bootstrap type drive circuit 10.

[0040] Also, by inserting a second bootstrap capacitor Cb2 between the first control switch SW1 and the second control switch SW2, it is possible to prevent a direct current from flowing between the first control switch SW1 and the second control switch SW2. Therefore, even if at least one of the first control switch SW1 or the second control switch SW2 has a short circuit failure, the current is cut off by the second bootstrap capacitor Cb2, so a large current does not flow between both ends of the first control switch SW1 and the second control switch SW2.

[0041] Also, even if the first control switch SW1 and the second control switch SW2 are in the simultaneous on state due to factors such as noise being superimposed on the drive signal of the control circuit 13, the current is cut off by the second bootstrap capacitor Cb2, so a large through-current does not flow through the first control switch SW1 and the second control switch SW2.

[0042] Also, since the second bootstrap capacitor Cb2 is interposed between the first control switch SW1 and the second control switch SW2, it is also possible to prevent a leakage current from flowing from the main power supply or the load 20 to the ground potential via the first control switch SW1 and the second control switch SW2 before the circuit is started.

[0043] Thus, since it is possible to prevent a large current from flowing between both ends of the first control switch SW1 and the second control switch SW2, it is not necessary to employ expensive elements with high current withstand performance for the first control switch SW1 and the second control switch SW2, and the costs of the first control switch SW1 and the second control switch SW2 can be suppressed. Also, since the simultaneous on of the first control switch SW1 and the second control switch SW2 is allowed, it is not necessary to employ a high-precision and expensive dedicated IC for the control circuit 13, and the cost of the control circuit 13 can be suppressed. Also, since no off-leakage current flows through the first control switch SW1 and the second control switch SW, unnecessary power consumption can be suppressed.

[0044] From the above, it is possible to realize a bootstrap-type drive circuit 10 that is low-cost, highly safe, suppresses an increase in power consumption, and has high control versatility.

[0045] The present disclosure has been described above based on embodiments. The embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of their components and processing processes, and that such modifications are also within the scope of the present disclosure.

[0046] In the embodiment described above, an example was explained in which Nch-MOSFETs were used for the high-side switching element Q1 and the low-side switching element Q2. However, NPN bipolar transistors may also be used for the high-side switching element Q1 and the low-side switching element Q2. In that case, "gate," "source," and "drain" are read as "base," "emitter," and "collector," respectively. Alternatively, IGBTs (Insulated Gate Bipolar Transistors) may be used for the high-side switching element Q1 and the low-side switching element Q2. In that case, "gate," "source," and "drain" are read as "gate," "emitter," and "collector," respectively.

[0047] The embodiments may be specified by the following items.

[0048] [Item 1] A first bootstrap capacitor (Cb1) connected between a high-side ground line (L2) connected to the connection point of a totem-pole connected high-side switching element (Q1) and a low-side switching element (Q2), and a high-side power supply line (L1) connected to a control power supply potential (VDD), wherein the high-potential terminal is connected to the high-side power supply line (L1) and the low-potential terminal is connected to the high-side ground line (L2); a bootstrap diode (Db) connected between the control power supply potential (VDD) and the high-potential terminal of the first bootstrap capacitor (Cb1) in the forward direction from the control power supply potential (VDD) to the first bootstrap capacitor (Cb1); a high-side drive circuit (11) connected between the high-side power supply line (L1) and the high-side ground line (L2), which outputs a drive signal corresponding to the high-side control signal to the control terminal of the high-side switching element (Q1) to control the on / off state of the high-side switching element (Q1); A voltage-holding capacitor (Ch) having its high-potential terminal connected to the high-side power line (L1) and its low-potential terminal connected to the high-side ground line (L2); a voltage-holding diode (Dh) connected in the forward direction from the first bootstrap capacitor (Cb1) to the voltage-holding capacitor (Ch) between the high-potential terminal of the first bootstrap capacitor (Cb1) and the high-potential terminal of the voltage-holding capacitor (Ch); a first control switch (SW1) connected between the low-potential terminal of the first bootstrap capacitor (Cb1) and the low-potential terminal of the voltage-holding capacitor (Ch); a second bootstrap capacitor (Cb2) having its high-potential terminal connected to the connection point (N1) between the first bootstrap capacitor (Cb1) and the first control switch (SW1); and a second control switch (SW2) connected between the low-potential terminal of the second bootstrap capacitor (Cb2) and the low-side ground line (L3). A drive circuit (10) is provided. This allows for low cost, high safety, suppression of increased current consumption, and highly versatile control.[Item 2] When controlling the high-side switching element (Q1) to be always on and the low-side switching element (Q2) to be always off, the drive circuit (10) according to Item 1 further includes a control circuit (13) that alternately turns on / off the first control switch (SW1) and the second control switch (SW2). According to this, even when the low-side switching element (Q2) is always off, the drive voltage of the high-side switching element (Q1) can be continuously ensured. [Item 3] The drive circuit (10) according to Item 1 or 2, wherein the capacitance ratio of the first bootstrap capacitor (Cb1) and the second bootstrap capacitor (Cb2) is set according to the value of the control power supply potential (VDD). According to this, an appropriate drive voltage for turning on the high-side switching element (Q1) can be generated.

[0049] The present disclosure can be used in a bootstrap-type drive circuit for driving a semiconductor switching element.

[0050] 10 Drive circuit, 11 High-side drive circuit, 12 Low-side drive circuit, 13 Control circuit, 20 Load, Q1 High-side switching element, Q2 Low-side switching element, Cb Bootstrap capacitor, Cb1 First bootstrap capacitor, Cb2 Second bootstrap capacitor, Ch Voltage holding capacitor, Db Bootstrap diode, Dh Voltage holding diode, SW1 First control switch, SW2 Second control switch.

Claims

1. A first bootstrap capacitor connected between a high-side ground line connected to the connection point of a totem-pole connected high-side switching element and a low-side switching element, and a high-side power supply line connected to the control power supply potential, wherein the high-potential terminal is connected to the high-side power supply line and the low-potential terminal is connected to the high-side ground line; a bootstrap diode connected between the control power supply potential and the high-potential terminal of the first bootstrap capacitor in the forward direction from the control power supply potential towards the first bootstrap capacitor; a high-side drive circuit connected between the high-side power supply line and the high-side ground line, which outputs a drive signal corresponding to the high-side control signal to the control terminal of the high-side switching element to control the on / off state of the high-side switching element; a voltage-holding capacitor connected between the high-potential terminal of the first bootstrap capacitor and the high-potential terminal of the voltage-holding capacitor in the forward direction from the first bootstrap capacitor towards the voltage-holding capacitor; A drive circuit comprising: a first control switch connected between the low-potential terminal of the first bootstrap capacitor and the low-potential terminal of the voltage-holding capacitor; a second bootstrap capacitor having its high-potential terminal connected to the connection point between the first bootstrap capacitor and the first control switch; and a second control switch connected between the low-potential terminal of the second bootstrap capacitor and the low-side ground line.

2. The drive circuit according to claim 1, further comprising a control circuit that alternately turns the first control switch and the second control switch on and off when controlling the high-side switching element to be always on and the low-side switching element to be always off.

3. The drive circuit according to claim 1 or 2, wherein the capacitance ratio of the first bootstrap capacitor and the second bootstrap capacitor is set according to the value of the control power supply potential.

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