JP3339247B2 - Signal transmission circuit for IGBT gate drive circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a signal transmission circuit for transmitting a signal to a gate drive circuit of an IGBT (insulated gate bipolar transistor) used as a power semiconductor device constituting an inverter.

[0002]

2. Description of the Related Art At present, in order to transmit a signal to a gate drive circuit of an IGBT, a signal transmission system in which a signal circuit and a power circuit are electrically insulated by a photocoupler is often used. As shown in FIG. The primary side of the photocoupler PC, the configuration of connecting the open-collector TTL, the logic circuit (gate circuit) IC ₁ formed of a transistor and the like, and inputs the signals transmitted to the secondary side, through the gate resistor to the gate terminal of the IGBT To perform high-speed switching. The input circuit of the photocoupler PC, which provided a noise suppression circuit according to the capacitor C ₁ and resistor R ₁ to R _3, to increase the margin for noise entering the like when the signal transmission path is long, stable operation It is trying to make it. Zener diode ZD ₁ is also one of the noise measures. Note that a limiting resistance R ₄ in the light emitting portion and the series of the photocoupler PC.

[0003]

[0006] However, in the signal transmission circuit of the primary side is open collector method photocoupler PC, for between a-b of the signal transmission line when the OFF signal input is open, the discharge path of the capacitor C ₁ And discharge is slower than charge. As a result, as shown in FIG. 5C, the primary voltage of the photocoupler PC has a larger OFF time constant than that of the photocoupler PC, and the photocoupler PC responds to the input signal.
OFF is slower than ON. If noise enters the signal transmission line after the OFF signal is input as shown in FIG. 5D, the noise superimposed on the signal exceeds the ON level and the inverter circuit malfunctions as shown in FIG. 5E. Is more likely to cause If the off time constant is small as shown in FIG. 5B, the noise does not reach the on level due to noise alone as shown in FIG.

Therefore, the present invention solves the above-mentioned problems, and can reduce the off-time, thereby improving the noise immunity.
It is an object to provide a signal transmission circuit for a GBT gate drive circuit.

[0005]

According to the present invention, the primary side of a photocoupler transmits a signal by an open collector system, and the input circuit of the photocoupler uses a CR as a countermeasure against noise.
In a signal transmission circuit for an IGBT gate drive circuit provided with a circuit, a transistor is provided between two lines on the signal generating side so as to be turned on at the time of an off signal and to directly pull a potential to the off side.
It is characterized in that discharge of the capacitor is promoted .

[0006]

When turned off, a bypass circuit is formed in the discharge path of the capacitor or the potential is forcibly reduced. When turned on, these circuits are operatively unrelated and operate quickly. That is, only the off time constant can be reduced without changing the on time constant, and the noise immunity is improved.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below with reference to the embodiments shown in the drawings.

FIG. 1 shows a first embodiment of a signal transmission circuit for an IGBT gate drive circuit according to the present invention. In the figure, PC is a photo-coupler, IC ₁ is a logic circuit of the open collector connected to the primary side of the photocoupler PC (gate circuit). The resistor R ₁ to the signal generator side of the signal transmission path is provided, it is provided with a CR circuit to increase the margin for noise in the photocoupler input. Also, by connecting a resistor R ₄ to the light-emitting portion and the series of the photocoupler PC.

The CR circuit includes resistors R ₃ , R ₂₁ , R ₂₂ ,
It comprises a capacitor C ₁ , a Zener diode ZD ₁ , and a diode D ₁ . The resistors R ₂₁ and R ₂₂ are obtained by dividing the resistor R ₂ of the conventional example (FIG. 4) into _two , and the diode D ₁ is connected between the dividing point and the terminal of the capacitor C ₁ . The diode D ₁ forms a bypass circuit for the resistors R ₃ and R ₂₁ when the capacitor C ₁ is discharged.
_21, R ₂₂ is selected in a suitable resistance value.

Next, the operation will be described. When the ON signal input, be the same circuit as the conventional example omitting diode D _1, immediately turns on. During off, discharge of the capacitor C ₁ is carried out a diode D ₁ and a resistor R ₂₂ as a discharge path. As a result, the ON time constant does not change, and only the OFF discharge time constant decreases, and the noise immunity improves.

Embodiment 2 is shown in FIG. In Example 2, the PNP transistor Tr ₁ is provided between the cathode-side signal transmission path of the Zener diode ZD _1, it connects the diode D ₂ between its base and emitter. The insertion resistance (the resistance R _{3 in the} first embodiment) of the signal transmission path (the zener diode ZD ₁ side) is a parallel combined resistance of the resistances R ₃₁ and R ₃₂ , and the resistance R ₃₂ is connected in series with the diode D ₂ . Also,
Resistance R ₂ between the signal transmission line, the resistance R ₂₁ of Example 1, R ₂₂
Is the series combined resistance of

In the circuit having the above configuration, when an ON signal is input, the parallel combined resistance of the resistors R ₃₁ and R ₃₂ becomes an insertion resistance of the signal transmission line, and is quickly turned on with the same time constant as in the first embodiment. During off voltage drop of the resistor R ₃₁ with the discharge of the capacitor C ₁ is applied between the emitter and base of the transistor Tr _1, the transistor Tr ₁ is turned on. This potential by turning on the transistor Tr ₁ is forcibly pulled off side. That is, the off operation becomes faster, which is effective for improving the noise immunity.

Embodiment 3 is shown in FIG. In the third embodiment, an NPN transistor Tr ₀ is provided on the signal transmission line on the signal generation side, a resistor R ₀ is connected between the base and collector , and a signal is supplied to the base via a logic circuit (gate circuit) IC _0. The photocoupler input side has the same circuit configuration as the conventional example (FIG. 4).

In the circuit having the above configuration, when the ON signal is input, the transistor Tr ₀ is turned off, and is turned on quickly with the same time constant as in the first and second embodiments. With discharge of the capacitor C ₁ transistor Tr ₀ is turned on is promoted during off, the potential is forcibly pulled off side. As a result, the off operation becomes faster, and the noise immunity is improved.

[0015]

As described above, according to the present invention, a circuit for accelerating the discharge of a capacitor when an off signal is input is provided.
Since the off operation is accelerated, intrusion noise after the input of the off signal is less likely to reach the on level, and so-called noise immunity can be improved. In addition, the off-time can be reduced without changing the on-time constant. In particular, in the case of a circuit in which a transistor directly pulls the potential to the off side at the time of an off signal, the effect of shortening the off time is higher than in the case of forming a bypass circuit, and the noise immunity is significantly improved.

[Brief description of the drawings]

FIG. 1 is a circuit diagram showing Embodiment 1 of a signal transmission circuit for an IGBT gate drive circuit according to the present invention.

FIG. 2 is a circuit diagram showing Embodiment 2 of a signal transmission circuit for an IGBT gate drive circuit according to the present invention.

FIG. 3 is a circuit diagram showing a third embodiment of a signal transmission circuit for an IGBT gate drive circuit according to the present invention.

FIG. 4 is a circuit diagram showing a conventional example of a signal transmission circuit for an IGBT gate drive circuit.

5A and 5B are waveform diagrams for explaining a signal transmission state of a signal transmission circuit, where FIG. 5A is a signal, FIG. 5B is a photocoupler input (ideal circuit), and FIG. 5C is a photocoupler input (conventional example). (D) shows intrusion noise, (e) shows a photocoupler input when noise enters (ideal circuit), and (f) shows a photocoupler input when noise enters (conventional circuit).

[Explanation of symbols]

PC ... logic circuit R ₁ optocoupler IC ₁ ... open collector _{~R 4, R 21, R 22} , R 31, R 32 ... resistance C ₁ ... capacitor ZD ₁ ... Zener diode D _1, D ₂ ... diode Tr ₀ , Tr ₁ ... transistor

──────────────────────────────────────────────────続 き Continued on front page (51) Int.Cl. ⁷ Identification code FI H03K 17/78 H03K 17/56 Z

Claims (1)

(57) [Claims] 1. A signal transmission for an IGBT gate drive circuit in which a primary side of a photocoupler transmits a signal in an open collector system and a CR circuit including a capacitor C and a resistor R is provided in an input circuit of the photocoupler as a countermeasure against noise. In the circuit, the collector of the transistor between the signal transmission circuits on the signal generation side
・ Connect the emitter and base transistor
Connect a resistor between the
Constitute the circuit for supplying a signal through, at the time of ON signal input, and turns off the transistor, the off signal
Sometimes, the transistor is turned on and the potential is directly turned off.
A signal transmission circuit for an IGBT gate drive circuit, characterized in that the discharge of the capacitor is promoted .