Bootstrap circuit and semiconductor device

Abstract

To provide a bootstrap circuit suitable for a power supply of a high side driver for driving a high side switch element of a power device in which switch elements are bridge-connected.SOLUTION: A bootstrap circuit B / S for supplying electric power from a power supply on a low side to a high-side driver DrH for turning on / off a high-side switch element QH of bridge-connected switch elements includes a plurality of series-connected diode groups (D1 to Dn), and a switch SW which is connected in parallel with the diode groups (D2 to Dn) excluding at least the diode D1 connected to the power supply of the high-side driver among the diode groups. The switch SW is turned off according to a dead time signal of the bridge-connected switch elements.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a bootstrap circuit suitable for use as a power supply for a high-side driver that drives a high-side switch element of a power device in which switch elements are bridge-connected. [Background technology]

[0002] In recent years, in application circuits such as PWM inverters and LLC circuits, bootstrap circuits have been used as the power supply for circuits that drive the high side of two switching elements connected in series between a high potential (high side) and a low potential (low side) in a full-bridge or half-bridge configuration. In such a bridge circuit, when the high-side switch element is off and the low-side switch element is on, the gate-source voltage (gate voltage) of the high-side switch element connected to the drive power supply is secured by charging the boot capacitor included in the bootstrap circuit.

[0003] In this type of bootstrap circuit, if the load of the bridge circuit is an inductive load (such as a motor or inductor), the potential at the connection point between the bridge circuit and the load becomes negative, and the charging voltage of the boot capacitor may become higher than the allowable gate voltage (allowable gate voltage) of the high-side switch element, resulting in so-called overcharging. If the boot capacitor becomes overcharged, the signal input to the gate of the switching element may become higher than the allowable gate voltage, which may cause a malfunction. Here, a bootstrap circuit is disclosed that aims to provide a drive voltage that can reliably and stably drive a high-side switching element (Patent Document 1). In Patent Document 1, the boot capacitor voltage of the bootstrap is monitored, and if an overvoltage is detected, the impedance of the resistor connected in series with the bootstrap diode is switched by a switch to prevent the boot capacitor voltage from rising too high.

[0004] Alternatively, as a means of generating the boot capacitor voltage, the boot capacitor is first charged to the same voltage as the power supply, and the negative side of the boot capacitor is raised to the power supply voltage of the control circuit, doubling the voltage on the positive side of the capacitor relative to GND, thereby achieving low Ron and high-speed switching (Patent Document 2).

[0005] Alternatively, by switching the charging path of the bootstrap voltage between startup and normal operation, the high-side switching element can be operated without any problems even immediately after startup (Patent Document 3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Republished WO2019 / 193805 [Patent Document 2] Patent No. 6177573 [Patent Document 3] Japanese Patent Application Laid-Open No. 2002-330064 Summary of the Invention [Problem to be solved by the invention]

[0007] However, to detect overvoltage by monitoring the bootstrap boot capacitor voltage as in Patent Document 1 (Prior Art 1), an overvoltage detection circuit must be provided in parallel with the boot capacitor and the bootstrap resistance value on the low side must be switched via a level shift circuit. This requires an overvoltage detection circuit and a level shift circuit, and if the bridge circuit has a high withstand voltage, a high-voltage element must also be used in the level shift circuit, resulting in a problem of increased circuit size. Furthermore, using a comparator, for example, in the overvoltage detection circuit increases the current consumption of the bootstrap circuit, further increasing the size of the bootstrap circuit. Furthermore, when the negative terminal of the boot capacitor is connected to the control power supply voltage to double the voltage as in Patent Document 2 (prior art 2), the problem of an increased size of the bootstrap circuit also occurs. Furthermore, when the charging path of the bootstrap voltage is switched between startup and normal operation as in Patent Document 3 (prior art 3), the problem of an increased size of the bootstrap circuit also occurs.

[0008] An object of the present invention is to provide a simple circuit configuration that adjusts the voltage of the boot capacitor of the bootstrap circuit so that it does not rise even when the potential at the connection point between the bridge circuit and the load becomes negative. [Means for solving the problem]

[0009] A bootstrap circuit supplies power from a power supply on a low side to a high side driver that drives on and off high side switch elements of bridge-connected switch elements, the bootstrap circuit including: a plurality of series-connected diode groups; a switch connected in parallel with the remaining diode groups excluding at least the diodes connected to the power supply of the high side driver among the plurality of diode groups; a dead time unit that outputs a dead time signal that prevents simultaneous on-operation of the bridge-connected switch elements; a control circuit that generates a drive signal that drives on and off the bridge-connected switch elements; and a dead time signal The pulse width of Extension period Outputs a signal extended by a time extension circuit, Control circuit While a negative voltage is generated at the connection point between the high-side switch element and the low-side switch element of the bridge-connected switch elements, the bridge-connected switch elements are simultaneously in the low-side outputting the dead time signal during a dead time period in which the the dead time signal A signal whose pulse width is extended by the extension period The switch is turned off by [Effects of the Invention]

[0012] According to the present invention, it is possible to control a short-circuiting switch connected in parallel to a group of multiple bootstrap diodes on the low side, thereby simplifying the circuit. Furthermore, even when the bridge circuit, driver, and bootstrap circuit are configured using semiconductor integrated circuits, the remaining diodes, excluding the diode connected to the power supply of the high-side driver, and the switches connected in parallel can be configured using low-voltage elements, which has the advantage that the size of the bootstrap circuit can be kept the same as usual. Furthermore, by canceling out the forward voltage of the regenerative diode connected in parallel with the bridge circuit element or the parasitic diode of the bridge circuit element, which is a factor in increasing the boot capacitor voltage, with the forward voltage of the series diode used in this invention, it is possible to generate a stable bootstrap voltage over a wider temperature range. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a configuration diagram including a bootstrap circuit and a high-side driver circuit and their peripherals according to the first embodiment. [Figure 2] FIG. 2 is a timing chart showing the operation of each part of the first embodiment. [Figure 3] FIG. 3 is an application circuit diagram of the first embodiment shown in FIG. [Figure 4] FIG. 4 is a timing chart showing the operation of each part of the application circuit diagram of the first embodiment. [Figure 5] FIG. 5 is a configuration diagram including a bootstrap circuit and a high-side driver circuit and their peripherals according to the second embodiment. [Figure 6] FIG. 6 is a timing chart showing the operation of each part of the second embodiment.

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the bootstrap circuit of the present invention will be described with reference to the accompanying drawings.

[0015] (First embodiment) 1 is a block diagram of a bootstrap circuit and a high-side driver circuit according to a first embodiment of the present invention, including their peripheral components. The block diagram shown in FIG. 1 corresponds to a circuit for one arm of a three-phase PWM inverter, for example.

[0016] In the configuration diagram shown in Figure 1, a high-side switch element QH and a low-side switch element QL that form a half-bridge circuit are connected to both ends of an input power supply 2. The source of the high-side switch element QH, the drain of the low-side switch element QL, and one terminal of a winding L1 are also connected. A control circuit 4 generates PWM signals that control the source of the high-side switch element QH and the low-side switch element QL, and one of the PWM signals output from the control circuit 4 is output as a gate signal VgH to the gate terminal of the high-side switch element QH via a level shift circuit L / H, which level-shifts and transmits the signal to the high side, and a gate driver DrH. The other PWM signal output from the control circuit 4 is output as a gate signal VgL to the gate terminal of the low-side switching device QL via the gate driver DrL. The control power supply voltage Vcc is supplied to the control circuit 4, the gate driver DrL, and the bootstrap circuit B / S, and is also supplied to the level shift circuit L / H and the gate driver DrH via the bootstrap circuit B / S.

[0017] The control circuit 4 detects a reference value serving as a reference and, for example, the current flowing through winding L1, compares the detected current value with the reference value, and outputs the difference between the current value and the reference value as an error signal from a command value unit 41 to a PWM generation unit 42. The PWM generation unit 42 generates a PWM signal based on the received error signal and also generates a signal with the generated PWM signal phase inverted by 180 degrees, and outputs the two signals to a dead time unit DT. The dead time unit DT provides a dead time period with a predetermined duration for each PWM signal at the timing when the two signals with different phases from the PWM generation unit 42 switch between high and low. This prevents the high-side switch element QH and the low-side switch element QL from turning on simultaneously, thereby preventing the flow of a short-circuit current. This dead time signal is output to the bootstrap circuit B / S as an on / off signal for the switch SW.

[0018] The bootstrap circuit B / S supplies power supply voltage to the high-side driver DrH and the level shift circuit L / S via a series-connected circuit of diodes D1 and D2 to Dn (n is an integer). The bootstrap circuit B / S charges the capacitor Cb when the low-side switch element QL is in the on state or when the potential at the connection point Vs between the source of the high-side switch element QH and the drain of the low-side switch element QL becomes close to GND.

[0019] Here, the anode of diode Dn is connected to the positive pole of the control power supply voltage Vcc, and the cathode of diode D1 connected in series with diode Dn is connected to one terminal of capacitor Cb and is connected to the positive power supply terminal of high-side driver DrH and level shift circuit L / S. The other terminal of the capacitor Cb is connected to the GND terminal of the high-side driver DrH and to a connection point Vs between the source of the high-side switching element QH and the drain of the low-side switching element QL. A switch SW is connected between the anode of the diode D2 and the cathode of the diode Dn, and the switch SW is turned on / off based on a dead time signal output from the dead time section DT. Here, only the withstand voltage of the diode D1 needs to be equal to or higher than the withstand voltage of the high-side switching element QH and the low-side switching element QL, and the withstand voltage of the diodes D2 to Dn needs to be about 10 to several tens of volts or more.

[0020] FIG. 2 is a timing chart showing the operation of each part of the first embodiment. When the waveform at the connection point Vs between the source of the high-side switching element QH and the drain of the low-side switching element QL is at a high voltage, the high-side switching element QH is on, the first drive signal VGH is high, and the second drive signal for the low-side switching element QL is low. At this time, the current IL flowing through the winding L1 increases over time. When the first drive signal VGH changes from high to low at time t1, the high-side switch element QH turns off, and the current IL flowing through the winding L1 reverses from increasing to decreasing. Next, the period from time t1 to t2 is a dead time period, during which both the first drive signal VGH and the second drive signal VGL remain low. During this dead time period, a dead time signal is output from the dead time section DT, turning off the switch SW of the bootstrap circuit B / S. Between times t1 and t2, the voltage at the connection point Vs between the source of the high-side switching element QH and the drain of the low-side switching element QL drops from the input power supply voltage Vin to a negative voltage lower than GND. This is due to the forward voltage of the diode DL connected in parallel to the low-side switching element QL caused by the regenerative current of the winding L1. In addition, due to the influence of wiring impedance other than that of the winding L1, a negative voltage is superimposed on the forward voltage of the diode DL. At time t2, the second drive signal VGL changes from low to high, turning on the low-side switching element QL, and the Vs voltage becomes approximately the GND voltage. Here, the voltage supplied to the power supply of the high-side driver DrH from time t1 to t2 is (control power supply voltage Vcc) + (absolute value of negative voltage), but since the switch SW of the bootstrap circuit B / S is turned off, the forward voltages of the diodes D1 to Dn are subtracted from this voltage. Therefore, by setting and connecting the number n of diodes so that the negative voltage and the forward voltages of the diodes D1 to Dn are offset, the power supply voltage of the high-side driver DrH can be prevented from being overcharged by the negative voltage. Furthermore, the diodes D2 to Dn may be low-voltage diodes, which has the advantage that the chip area required can be small when considering incorporating the high-side driver DrH, the diodes D2 to Dn of the bootstrap circuit B / S, and the switch SW into the integrated circuit that constitutes the control circuit 4. Furthermore, the on / off signal of the switch SW that short-circuits the diodes D2 to Dn is a dead time signal, so there is no need to generate a new control signal, and there is an advantage that the configuration can be simplified. Furthermore, the forward voltage of the regenerative diode of the low-side switch element QL or the parasitic diode DL of the element and the forward voltage of the diodes D1 to Dn are cancelled out at the ambient temperature, making it possible to generate a bootstrap voltage that is stable across a range of temperatures.

[0021] (Application example of the first embodiment) Fig. 3 is an application circuit diagram of the first embodiment shown in Fig. 1. The difference from Fig. 1 is that the control circuit 4 in Fig. 1 is replaced with a control circuit 4a equipped with a time extension circuit (Extend) 44. The control circuit 4a extends the time of the dead time signal output from the dead time unit through the time extension circuit 44.

[0022] 4 is a timing chart showing the operation of each part of the application circuit diagram of the first embodiment, which is set under the condition that a current larger than the winding current IL shown in FIG. When the first drive signal VGH changes from high to low at time t1a, the high-side switch element QH turns off, and the current IL flowing through the winding L1 reverses from increasing to decreasing. Next, the period from time t1a to t2a is a dead time period, during which both the first drive signal VGH and the second drive signal VGL remain low. At this time t1a, a dead time signal is output from the dead time circuit DT, and the switch SW of the bootstrap circuit B / S is turned off via the time extension circuit (Extend) 44. When the dead time signal between times t1a and t2a is input, the time extension circuit (Extend) 44 outputs a pulse width that is extended from times t1a to t3a, which is longer than this period. Similar to the timing chart of Figure 2, the voltage at the connection point Vs between the source of the high-side switch element QH and the drain of the low-side switch element QL drops from the input voltage Vin to a negative voltage lower than GND from time t1a to t2a. In Figure 4, this negative voltage is caused by the large regenerative current flowing through the winding L1 and the increased influence of the wiring impedance other than that of the winding L1, and the superimposed negative voltage also becomes relatively large. Next, at time t2a, the second drive signal VGL changes from low to high, turning on the low-side switching element QL, and the Vs voltage becomes approximately the GND voltage. The voltage supplied to the power supply of the high-side driver DrH from time t1a to time t2a is (voltage Vcc of the control power supply)+(absolute value of the negative voltage)−(forward voltages of the diodes D1 to Dn). However, if the turn-on speed of the low-side switch element QL rises with a slight delay due to the increase in the current IL of the winding current L1, in the configuration of Figure 1, the switch SW of the bootstrap circuit B / S will change from off to on first, and there is a possibility that the voltage supplied to the power supply of the high-side driver DrH will be overcharged, albeit for a moment. Therefore, by extending the dead time signal to time t3a via the time extension circuit (Extend) 44, the switch SW of the bootstrap circuit B / S is turned off so that the negative voltage is reliably cancelled out by the forward voltages of the diodes D1 to Dn, thereby preventing overcharging due to the negative voltage. Furthermore, when considering incorporating the high-side driver DrH, the diodes D2 to Dn of the bootstrap circuit B / S, and the switch SW into the integrated circuit that constitutes the control circuit 4a, there is also the advantage that the chip area required can be small, similar to the first embodiment.

[0023] (Second embodiment) FIG. 5 is a configuration diagram including a bootstrap circuit and a high-side driver circuit and their peripherals according to the second embodiment. In the first embodiment, the on / off control of the switch SW of the bootstrap circuit B / S is performed by a dead time signal. However, in the second embodiment, instead of the dead time signal, an off signal of the high-side switch element QH is used as a trigger to generate a one-shot pulse signal having a predetermined pulse width that is longer than the dead time signal, and the on / off control of the switch SW is performed.

[0024] Figure 5 is a configuration diagram of the bootstrap circuit and high-side driver circuit of the second embodiment, including their peripherals. The difference from Figure 1 is that the control circuit 4 in Figure 1 is replaced with a control circuit 4b equipped with a one-shot circuit (1Shot) 45. The PWM generation unit 42b of the control circuit 4b incorporates a dead time unit DT. By setting the predetermined pulse width output by the one-shot circuit (1Shot) 45 to be longer than the time width of the dead time signal, it is possible to obtain substantially the same effect as in the application example of the first embodiment. Fig. 6 is a timing chart showing the operation of each part of the second embodiment. Although a dead time signal is not shown in Fig. 6, during the period (dead time) when the first drive signal VGH and the second drive signal VGL are simultaneously low, a one-shot pulse is generated from the turn-off time t1b of the high-side switch QH until t3b to control the switch SW of the bootstrap circuit B / S to be turned off. Therefore, by controlling the switch SW to be turned off with a signal longer than the dead time signal, it is possible to obtain the same effect as the application example of the first embodiment.

[0025] As described above, according to the second embodiment, without directly obtaining a dead time signal, a one-shot pulse having a predetermined pulse width longer than that of the dead time signal is generated using the off signal of the high-side switch element QH as a trigger to control the switch SW of the bootstrap circuit B / S to be turned off. This makes it possible to reliably prevent overcharging of the power supply voltage of the high-side driver DrH due to the generation of a negative voltage at the Vs terminal immediately after the high-side switch element QH is turned off. Furthermore, when considering incorporating the high-side driver DrH, the diodes D2 to Dn of the bootstrap circuit B / S, and the switch SW into the integrated circuit constituting the control circuit 4b, there is also the advantage that the chip area required can be small, similar to the first embodiment.

[0026] Although the embodiments of the present invention have been described above, the above embodiments are merely examples for embodying the technical idea of ​​the present invention, and the individual configurations, combinations, etc. are not limited to those described above. The present invention can be implemented with various modifications within the scope of the gist of the present invention. [Industrial Applicability]

[0027] The present invention is applicable to an IPM used in a PWM inverter, etc. [Explanation of symbols]

[0028] 1, 1a, 1b Configuration diagram including the bootstrap circuit and high-side driver circuit and their peripherals 2 input power 3 Control power supply 4, 4a, 4b Control circuit 41 Command value section 42, 42b PWM generation section 43 Dead Time Section 44 Extension time circuit 45 One-shot circuits B / S bootstrap circuit Cb capacitor D1~Dn, DH, DL diodes DrH High-side driver DrL Low-side driver L1 winding L / S level shift circuit QH High-side switch element QL low-side switch element SW switch

Claims

1. A bootstrap circuit that supplies power from a power supply on a low side to a high side driver that drives on and off a high side switch element of bridge-connected switch elements, a plurality of series-connected diodes; a switch connected in parallel with the remaining diode groups among the plurality of diode groups except for at least the diodes connected to the power supply of the high-side driver; a control circuit having a dead time unit that outputs a dead time signal that prevents simultaneous ON operations of the bridge-connected switch elements, and that generates a drive signal that drives the bridge-connected switch elements to turn ON and OFF; a time extension circuit that outputs a signal in which the pulse width of the dead time signal is extended by an extension period; Equipped with the control circuit outputs the dead time signal during a dead time period in which the bridge-connected switch elements simultaneously remain low while a negative voltage is generated at a connection point between a high-side switch element and a low-side switch element of the bridge-connected switch elements, and turns off the switch with a signal whose pulse width is extended by an extension period.

2. 2. The bootstrap circuit according to claim 1, wherein the control circuit sets the number of the diode groups so as to cancel out the negative voltage.

Images