JP2019068551A - Gate drive circuit - Google Patents

Abstract

To provide a gate drive circuit in which an element for a countermeasure against erroneous ignitions can be prevented from being broken.SOLUTION: Gate drive circuits 31, 32 include control circuits Z1 for performing switching control of switching elements S1, S2 (first switching elements) constituting upper and lower arms, and gate resistances Rconnected between gate terminals of the switching elements S1, S2 and the control circuits Z1, respectively. A series circuit including a diode Dthat establishes connection in a forward direction from the gate terminal of the switching element S1, S2 toward the control circuit Z1 and including a resistance Ris connected in parallel with the gate resistance R. A transistor Q(second switching element) which is turned on by the potential difference between both ends of the resistance Rin the series circuit is connected between the gate terminal of the switching element S1, S2 and a source terminal (low-potential side terminal).SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gate drive circuit for driving switching elements constituting upper and lower arms.

As shown in FIG. 4, when the upper and lower arms are constituted by switching elements S1 and S2 such as SJ-MOSFET and SiC-MOSFET having high switching speed, the opposite side of the turned-on switching element (S1 in the example shown in FIG. 4) The drain-source voltage V _{DS of the} switching element (S2 in the example shown in FIG. 4) rises at a large speed dV _DS / dt. Then, as indicated by the arrows in FIG. 1, a surge current (I _DG = C _DG × dV _DS / dt) flows into the driver circuit 10 via the mirror capacitance C _DG of the switching element S2. Then, there are times when the gate potential V _GS rises to V _GS = (R ₁ + R ₂ ) × I _DG by the gate resistance R ₁ and the gate impedance R ₂ of the control circuit Z ₁ to cause a false ignition.

A gate drive circuit as shown in FIG. 5 has been proposed as a countermeasure against such erroneous firing (see, for example, Patent Documents 1 and 2). In the gate driver circuits 11 and 12 shown in FIG. 5 (a), by connecting the transistor Q ₁ to turn on the gate potential V _GS is increased by surge current between the gate and source of the switching element S2, prevent false firing doing. Further, In FIG. 5 (b) are shown the gate driver circuits 21 and 22, between the gate and source of the transistor Q _1, the switching element S2 the series circuit composed of the capacitor C ₁ Metropolitan to turn the gate potential V _GS is increased by surge current By connecting to, false firing is prevented.

Unexamined-Japanese-Patent No. 2003-324966 Unexamined-Japanese-Patent No. 2012-239061

However, in the prior art, the gate potential V _GS of the switching element S 2 smoothly rises due to the gate capacitance C _G and the gate resistance R ₁ at turn-on. Therefore, instantaneous potential difference is generated across the gate resistor R _1. That is, since the gate capacitance C _G is 0V to the gate voltage V _G is applied, the moment of the gate voltage rise regarded as short-equivalent circuit at the time of the gate voltage rise of the gate driver circuits 11 and 12, FIG. 6 As shown in. Therefore, when the gate voltage rise, the base of the transistor Q ₁ to the gate voltage V _G is connected in parallel to the gate resistor R ₁ - to emitter voltage V _be applied. Therefore, the gate voltage _{V G} (e.g., 10～15V) the base of the transistor _{Q 1} - if above the maximum rating of the emitter voltage Vbe (e.g., 5～7V), the transistor _{Q 1} is thus reached damaged by stress caused by overvoltage There is a problem that there is a fear.

  An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a gate drive circuit capable of preventing damage to a device for preventing false firing.

  A gate drive circuit according to the present invention comprises a control circuit that performs switching control of first switching elements that constitute upper and lower arms, and a gate resistance connected between the gate terminal of the first switching elements and the control circuit. A series circuit including a diode connected in a forward direction from the gate terminal of the first switching element toward the control circuit, and a resistor is connected in parallel with the gate resistor; A second switching element which is turned on by a potential difference between both ends of the resistor in the circuit is connected between the gate terminal of the first switching element and the low potential side terminal.

  According to the present invention, when the gate voltage rises by the control circuit, the overvoltage which is a stress is not applied to the second switching element provided as an element for preventing false firing, so that the second switching element is damaged. This is effective in that the false firing can be prevented stably.

FIG. 1 is a circuit configuration diagram showing a circuit configuration of an embodiment of a gate drive circuit according to the present invention. It is an equivalent circuit at the time of gate voltage rising of the gate drive circuit shown in FIG. It is a circuit block diagram which shows the circuit structure of other embodiment of the gate drive circuit based on this invention. It is explanatory drawing explaining the false ignition at the time of comprising an upper and lower arm by a switching element. It is a circuit block diagram which shows the circuit structure of the conventional gate drive circuit. It is an equivalent circuit at the time of gate voltage rising of the gate drive circuit shown to Fig.5 (a).

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the following embodiments, the same reference numerals are given to the configurations showing the same functions, and the description will be appropriately omitted.

  Referring to FIG. 1, the gate drive circuits 31 and 32 of the present embodiment are circuits for driving the switching elements S1 and S2 constituting the upper and lower arms, respectively. Since the gate drive circuits 31 and 32 have the same configuration, the gate drive circuit 32 will be described below, and the description of the gate drive circuit 31 will be omitted.

  As the switching elements S1 and S2, SJ (super junction) MOSFETs or SiC (silicon carbide) MOSFETs having a high switching speed are used.

The gate drive circuit 32 includes a control circuit Z1 controlling switching of the switching element S2, a gate resistor _{R 1,} a diode _{D 1,} a resistor _{R 3,} and a transistor _{Q 1.} Incidentally, _{R 2} shown in FIG. 1 is a gate impedance of the control circuit Z1.

Gate resistor R _1, for the purpose of preventing parasitic oscillation in the switching element S2, is connected between the gate terminal (control terminal) and the control circuit Z1 of the switching element S2.

Diode D ₁ has a cathode to the connection point of the gate resistor R ₁ and the control circuit Z1, an anode is connected to a connection point between the gate terminal of the gate through a resistor R ₃ resistor R ₁ and the switching element S2 . That is, the diode D1 that connects in a forward direction toward the control circuit Z1 from the gate terminal of the switching element S2, a series circuit composed of the resistor R ₃ Metropolitan is connected in parallel to the gate resistor R _1.

Transistor Q ₁ is connected between the gate terminal and the source terminal of the switching element S2 (the low potential side terminal), the surge current flowing from the gate terminal of the switching element S2 when the gate potential V _GS increases, the resistance R ₃ It turns on by the potential difference between both ends, clamps the gate potential V _GS to the source potential V _S , and prevents false ignition.

In this embodiment, a PNP transistor as the transistor Q _1, to the connection point of the emitter and the gate terminal of the gate resistor R ₁ and the switching element S2, the source terminal of the collector is the switching element S2, the base of the diode D ₁ It is connected to the connection point of the anode and the resistor R _3.

FIG. 2 is an equivalent circuit when the gate voltage of the gate drive circuit 32 rises. As shown in FIG. 2, the base of the transistor Q ₁ - emitter is represented by a diode D _Q. Therefore, can be regarded as a series circuit comprising a diode D ₁ and the diode D _Q is connected in parallel to the gate resistor R _1, the inverse series circuit consisting of a diode D ₁ and diode D _Q when the gate voltage rise so that the direction of the gate voltage V _G is applied. In this case, the voltage applied to the diode D _Q will be determined by the impedance of the diode D ₁ and the diode D _{Q, (the} transistor Q ₁ base - emitter) diode D _Q in parallel resistor R ₃ is because it is connected, the gate voltage V _G will be predominantly applied to the diode D _1. Thus, since the over-voltage between base-emitter (diode D _Q) of the transistor Q ₁ when the gate voltage rise is not applied, it is possible to prevent the transistor Q ₁ is damaged.

Also, like the gate driving circuits 41 and 42 shown in FIG. 3, between the gate and source terminals of the switching elements S1, S2, it may be connected to the transistor Q _1, the capacitor C ₁ in series. By connecting the transistor Q _1, the capacitor C ₁ in series, the transistor Q ₁ is turned with the rise of the gate potential V _GS due to the surge current, the input capacitance of the switching elements S1, S2 is increased by the capacitor C ₁ . Therefore, the rise of the gate potential V _GS of the switching elements S1 and S2 is suppressed, and erroneous ignition is prevented.

Again, the transistor Q ₁ base - for emitters between the resistor R ₃ are connected in parallel, the gate voltage V _G at the gate voltage rise is predominantly applied to the diode D _1, the transistor Q ₁ is damaged Can be prevented.

As described above, according to the present embodiment, the control circuit Z1 that performs switching control of the switching elements S1 and S2 (first switching element) that constitute the upper and lower arms, and the gate terminals of the switching elements S1 and S2 and control a gate drive circuit 31, 32 having connected to the gate resistor R ₁ between the circuit Z1, a diode D ₁ to be connected to a forward direction toward the control circuit Z1 from the gate terminal of the switching element S1, S2 A transistor Q ₁ (second switching element) is connected in series with a resistor R ₃ and connected in parallel with the gate resistor R ₁ and turned on by the potential difference between both ends of the resistor R ₃ in the series circuit. It is connected between the gate terminal and the source terminal (low potential side terminal) of
With this configuration, when the gate voltage rise by the control circuit Z1, since the overvoltage to be stress is that there is no to be applied to the transistor Q ₁ which is provided as an element for false firing measures, it is possible to prevent breakage of the transistor Q _1, stable False firing can be prevented.

Further, in the present embodiment, the transistor Q ₁ is connected to the source terminal of the switching element S1, S2 via the capacitor C _1.
Even when employing this configuration, similarly for overvoltage becomes stress is prevented from being applied to the transistor Q _1, can prevent damage to the transistor Q _1, can be prevented stably Ayamaten arc.

  Although the present invention has been described above in terms of specific embodiments, it is needless to say that the above embodiments are merely examples and can be modified and implemented without departing from the spirit of the present invention.

11,12,21,22,31,32,41,42 gate driving circuit _D 1, _{D Q} diodes _{R 1} gate resistor _{R 2} gate impedance _{R 3} resistor _{Q 1} transistor Z1 control circuit

Claims (2)

A control circuit that performs switching control of a first switching element that constitutes the upper and lower arms;
A gate drive circuit comprising: a gate resistor connected between a gate terminal of the first switching element and the control circuit;
A series circuit including a diode connected in a forward direction from the gate terminal of the first switching element to the control circuit, and a resistor is connected in parallel with the gate resistor,
A gate drive circuit characterized in that a second switching element turned on by a potential difference between both ends of the resistor in the series circuit is connected between the gate terminal of the first switching element and the low potential side terminal. .   The gate drive circuit according to claim 1, wherein the second switching element is connected to the low potential side terminal of the first switching element via a capacitor.

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