JP2007318891A - Power circuit for driving switching element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a compact power circuit capable of preventing a supply voltage from being dropped by the discharge of a bootstrap capacitor in a drive circuit. <P>SOLUTION: When a switching element Q1 of an upper arm is turned off, a surge voltage caused by the inductance of wiring is generated, voltage V across the ends of the switching element Q1 becomes higher than the supply voltage V1 of a power supply E1 for loads temporarily, a charge current Ic flows to the positive electrode of the bootstrap capacitor C via a diode D2 for backflow prevention from a drain terminal D of the switching element Q1 of the upper arm and a Zener diode ZD1 for determining a voltage threshold, and the bootstrap capacitor C is charged. When the voltage across the ends of the bootstrap capacitor C becomes higher than the supply voltage V2 of a power supply E2 for control by the charge current Ic, the impedance of a Zener diode ZD2 is reduced, thus preventing the overvoltage of the bootstrap capacitor C. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a switching element driving power supply circuit, and more particularly to a bootstrap power supply circuit.

  In general, in an inverter or the like, two switching elements (main circuit elements) are connected by an arm, and an upper arm switching element and a lower arm switching element are alternately turned on / off and used. As a power supply circuit for driving such a switching element, for example, a bootstrap power supply circuit as shown in FIG. 3 is often used from the viewpoints of cost, physique, and the like.

  Switching elements Q1 and Q2 made of two MOSFETs are connected in series to the load power supply E1, and the high-voltage side drive circuit 1 connected to the gate terminal G of the switching element Q1 of the upper arm supplies power stored in the bootstrap capacitor C as a power source. And the low voltage side drive circuit 2 connected to the gate terminal G of the switching element Q2 of the lower arm is driven by the control power supply E2. When the switching element Q2 of the lower arm is turned on by the low-voltage side drive circuit 2 based on the input signal from the outside, the bootstrap capacitor C is charged by the control power supply E2 via the diode D1 and the current limiting resistor R, and the lower arm When the switching element Q2 is turned off, the high-voltage side drive circuit 1 is operated using the electric charge stored in the bootstrap capacitor C as a power source, and the switching element Q1 of the upper arm is turned on based on an input signal from the outside.

  In this way, by alternately switching on / off the switching element Q1 of the upper arm and the switching element Q2 of the lower arm, the source terminal S of the switching element Q1 of the upper arm and the drain terminal D of the switching element Q2 of the lower arm A pulse-like drive signal is output to the load 3 connected to the connection point.

  Here, if the switching element Q1 of the upper arm is kept on, the bootstrap capacitor C is discharged, and the power supply voltage of the high-voltage side drive circuit 1 is lowered. Therefore, for example, in the power supply circuit disclosed in Patent Document 1, a series circuit of an inductor and a switch element constituting a boost chopper circuit is connected in parallel with a control power supply for supplying a power supply voltage to the low-voltage side drive circuit, and the inductor A diode is inserted between the connection point of the switch element and the bootstrap capacitor so that the bootstrap capacitor can be charged at all times regardless of whether the switching element is on or off.

JP 2003-18821 A

  However, in the circuit of Patent Document 1, an inductor, a switch element, and a diode that constitute a boost chopper circuit are added to the power supply circuit shown in FIG. 3, and a circuit for turning on / off the switch element is not added. In other words, the problem arises that the number of parts increases and the power supply circuit becomes larger.

  The present invention has been made to solve such a conventional problem, and provides a power supply circuit that is small in size and can prevent a decrease in power supply voltage of a drive circuit due to discharge of a bootstrap capacitor. With the goal.

  A switching element driving power supply circuit according to the present invention is a power supply circuit for controlling on / off of a switching element by driving a drive circuit using a stored charge of a bootstrap capacitor as a power supply. A zener diode for determining the voltage threshold and a backflow prevention diode are connected in series between the drain terminal of the element and a bootstrap capacitor via the zener diode and the diode by the surge voltage generated when the switching element is turned off. The charging current flows.

  According to the present invention, switching is performed with a simple configuration in which a Zener diode for determining a voltage threshold and a diode for preventing backflow are connected in series between the positive electrode of the bootstrap capacitor and the drain terminal of the switching element. A bootstrap capacitor can be charged using a surge voltage generated at the time of turn-off of the element, and a power supply circuit capable of preventing a decrease in the power supply voltage of the drive circuit due to discharge of the bootstrap capacitor is realized.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 shows a configuration of a driving circuit including a switching element driving power supply circuit according to the embodiment. Switching elements (main circuit elements) Q1 and Q2 comprising two MOSFETs constituting the inverter are connected in series to the load power supply E1, and the high-voltage side drive circuit 1 is connected to the gate terminal G of the switching element Q1 of the upper arm. Yes. A bootstrap capacitor C is connected between a power supply line L1 connected to the control power supply E2 via the diode D1 and the current limiting resistor R and a reference line L0 to which the source terminal S of the switching element Q1 is connected.

A series circuit of a Zener diode ZD1 for determining a voltage threshold and a diode D2 for preventing a backflow is connected between the positive electrode of the bootstrap capacitor C and the drain terminal D of the switching element Q1 of the upper arm. A zener diode ZD2 for preventing overvoltage is connected in parallel with C.
Further, the low voltage side drive circuit 2 is connected to the gate terminal G of the switching element Q2 of the lower arm. Further, a load 3 is connected to a connection point between the source terminal S of the upper arm switching element Q1 and the drain terminal D of the lower arm switching element Q2.

That is, this drive circuit includes a Zener diode ZD1 for determining a voltage threshold value and a backflow preventing diode D2 in the conventional circuit shown in FIG. 3, and the positive electrode of the bootstrap capacitor C and the switching element Q1 of the upper arm. The zener diode ZD2 for preventing overvoltage is connected in series with the drain terminal D and in parallel with the bootstrap capacitor C.
The Zener diode ZD1 for determining the voltage threshold has a Zener voltage slightly higher than the difference ΔV = V1−V2 between the power supply voltage V1 of the load power supply E1 and the power supply voltage V2 of the control power supply E2. Shall.
The Zener diode ZD2 for preventing overvoltage has a Zener voltage that is approximately the same as the power supply voltage V2 of the control power supply E2, for example.

Next, the operation of this embodiment will be described. First, the low-voltage side drive circuit 2 receives power supply from the control power supply E2, and performs on / off control of the switching element Q2 of the lower arm based on an external input signal. When the switching element Q2 is turned on, a current flows from the control power supply E2 to the bootstrap capacitor C via the diode D1 and the current limiting resistor R, and thereby the bootstrap capacitor C is charged. At this time, the current limiting resistor R limits the charging current flowing through the bootstrap capacitor C so as not to become too large. When sufficient charging is performed, the voltage across the bootstrap capacitor C becomes the power supply voltage V2 of the control power supply E2.
Thereafter, when the lower arm switching element Q2 is turned off, the high-voltage side drive circuit 1 is operated using the electric charge stored in the bootstrap capacitor C as a power source, and the upper arm switching element Q1 is turned on based on an external input signal. .

In this way, the switching element Q1 of the upper arm and the switching element Q2 of the lower arm are alternately turned on / off, and the load connected to the connection point between the source terminal S of the switching element Q1 and the drain terminal D of the switching element Q2 3 outputs a pulse-like drive signal.
When the switching element Q1 of the upper arm is turned on, the charge accumulated in the bootstrap capacitor C is consumed by the high-voltage side drive circuit 1 as a power source, so that the voltage across the bootstrap capacitor C gradually decreases.

  Next, the upper arm switching element Q1 is turned off and the lower arm switching element Q2 is turned on. When the upper arm switching element Q1 is turned off, a surge voltage is generated due to the inductance of the wiring. As shown in FIG. 2, the voltage V across the switching element Q1 is temporarily higher than the power supply voltage V1 of the load power supply E1.

  At this time, the Zener diode ZD1 for determining the voltage threshold has a Zener voltage slightly higher than the difference ΔV = V1−V2 between the power supply voltage V1 of the load power supply E1 and the power supply voltage V2 of the control power supply E2. The voltage across the bootstrap capacitor C is lower than the power supply voltage V2 of the control power supply E2 due to power consumption by the high-voltage side drive circuit 1. Therefore, the impedance of the Zener diode ZD1 decreases, and as shown by the broken line in FIG. 1, the charging current flows from the drain terminal D of the switching element Q1 of the upper arm to the positive electrode of the bootstrap capacitor C through the diode D2 and the Zener diode ZD1. Ic flows and the bootstrap capacitor C is charged.

  Here, since the Zener diode ZD2 is connected in parallel with the bootstrap capacitor C, when the voltage across the bootstrap capacitor C becomes higher than the power supply voltage V2 of the control power supply E2 by the charging current Ic, the impedance of the Zener diode ZD2 This prevents the bootstrap capacitor C from becoming overvoltage.

As described above, the voltage threshold determining Zener diode ZD1 and the backflow preventing diode D2 are simply connected in series between the positive electrode of the bootstrap capacitor C and the drain terminal D of the switching element Q1 of the upper arm. With this simple configuration, the bootstrap capacitor C can be charged using the generated surge voltage even when the switching element Q1 of the upper arm is turned off.
Furthermore, if a Zener diode ZD2 is connected in parallel with the bootstrap capacitor C, an overvoltage of the bootstrap capacitor C can be prevented.

  The present invention can be applied not only to a drive circuit that performs on / off control of switching elements that constitute an inverter, but also to various circuits that turn on / off circuit elements using a bootstrap capacitor as a power source.

It is a figure which shows the structure of the drive circuit of the switching element provided with the power supply circuit which concerns on embodiment of this invention. It is a graph which shows the change of the voltage between both ends of the switching element at the time of turn-off of a switching element. It is a figure which shows the structure of the drive circuit provided with the conventional power supply circuit.

Explanation of symbols

  1 High-voltage side drive circuit, 2 Low-voltage side drive circuit, 3 Load, E1 Load power supply, E2 Control power supply, Q1 Upper arm switching element, Q2 Lower arm switching element, C Bootstrap capacitor, ZD1 Voltage threshold determination Zener diode, ZD2 Zener diode for overvoltage prevention, D2 Backflow prevention diode.

Claims (1)

In a switching element driving power supply circuit for controlling on / off of a switching element by driving a drive circuit using a stored charge of a bootstrap capacitor as a power supply,
A Zener diode for determining a voltage threshold and a diode for preventing a backflow are connected in series between the positive electrode of the bootstrap capacitor and the drain terminal of the switching element, and the Zener diode is caused by a surge voltage generated when the switching element is turned off. And a switching element driving power supply circuit, wherein a charging current flows through the bootstrap capacitor via the diode.

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