JPH05235722A - Switching element drive circuit - Google Patents

Abstract

PURPOSE:To provide the switching element drive circuit reducing a turn-on/turn- off time automatically and preventing a damage to a voltage drive switching element due to a surge voltage. CONSTITUTION:A switching element drive circuit which is driven by applying a voltage to a voltage drive switching element 1 provided with a load 2 between a collector and an emitter to drive the switching element 1 is provided with a variable gate resistor circuit 4 connected in series with a gate of the element 1, a current transformer CT detecting a load current Io fed to the load 2, a voltage detector 5 detecting a collector-emitter voltage of the element 1. The resistance of the variable gate resistor circuit 4 is controlled variably based on a change of the load current Io and whether or not a voltage is a surge voltage. Through the constitution above, the turn-on/turn-off time of the element is reduced automatically and the defect of the element 1 due to a surge voltage is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switching element drive circuit.

[0002]

2. Description of the Related Art Conventionally, as a switching element drive circuit configured to connect a load such as a motor between the collector and the emitter of a voltage drive type switching element and apply a voltage to the gate of the element to drive the element. Is
The following circuits are known.

That is, as shown in FIG. 6, as a voltage drive type switching element, for example, an IGBT (JEDE) is used.
C registered name: insulated gate bipolar transistor) 1 is used, and a load 2 and a power source E as a drive source of the load 2 are connected between the collector and the emitter of the IGBT 1. Inside the IGBT1, an element internal gate resistance Rg is connected on the gate side, and a damage prevention diode D for bypassing a counter electromotive current at the time of turn-off of the IGBT1 is connected between the collector and the emitter.

An external gate resistor RG is connected in series to the gate of the IGBT 1, and the drive circuit 3 is connected via the external gate resistor RG. Then, the drive circuit 3 is configured to apply a voltage between the gate and the emitter of the IGBT 1 to control the ON / OFF of the IGBT 1.

[0005]

By the way, in the switching element drive circuit using the voltage control type element as described above, the voltage control type element of the voltage control type element is changed depending on the resistance value of the external gate resistance connected in series to the gate. It is known to affect turn-on and turn-off times. Particularly, in the above-mentioned IGBT 1 used when handling a load current of a large amount, the effect on the turn-on / turn-off time based on the resistance value of the external gate resistance RG is significant.

The influence on the turn-on / turn-off time will be described based on the conventional example of FIG. 6. When the resistance value of the external gate resistor RG is larger than an appropriate value with respect to the load current I ₀ , the turn-on / turn-off of the IGBT 1 is performed. Time will increase. On the contrary, when the resistance value of the external gate resistor RG is smaller than an appropriate value, the turn-on / turn-off time of the IGBT1 becomes short, but an excessive surge voltage occurs between the collector and the emitter at the turn-on / turn-off of the IGBT1, If this exceeds the withstand voltage of the IGBT 1, the IGBT 1 may be damaged.

Therefore, in order to shorten the turn-on / turn-off time and prevent the IGBT 1 from being damaged by the surge voltage, the resistance value of the external gate resistor RG is set beforehand to an appropriate value for the load current I _0. There is a need.

However, in the conventional switching element drive circuit, the resistance value of the external gate resistor RG is fixed, so that the load current I is changed by replacing the load 2.
_{When 0} changes, it is necessary to replace the external gate resistance RG with a resistance value suitable for the load current I ₀ . For details, refer to the manufacturer's recommended gate resistance value, select and replace the external gate resistance RG that is compatible with the load current I _0, and if an excessive surge voltage is generated between the collector and emitter of the IGBT 1, use the external gate resistance RG. I was working on changing the RG to one with a higher resistance value.

Therefore, there has been a problem that it takes time to select and replace the external gate resistor RG according to the load current I ₀ . Further, the above circuit cannot be used for a load in which the magnitude of the load current I ₀ changes with time.

The present invention has been made to solve the above problems, and a first object thereof is a switching element capable of omitting the selection and replacement work of an external gate resistor even if the load current is changed. It is to provide a driving circuit. A second object is to provide a switching element driving circuit capable of preventing damage to the voltage control type switching element in advance, in addition to the first object.

[0011]

In order to achieve the above object, the present invention is, in the first invention, a switching method in which a voltage is applied to a voltage drive type switching element having a load between a collector and an emitter to drive the switching element. In the element drive circuit, a variable gate resistance circuit connected in series to the gate of the voltage driven switching element, a current detection unit that detects a load current supplied to the load, and a load detected by the current detection unit. Comprising a comparison means for comparing the detection signal of the current and a preset reference current value, and a control means for controlling the resistance value of the variable gate resistance circuit based on the comparison result of the current value comparison means. The summary is.

Further, in the second invention, the collector
In a switching element drive circuit that applies a voltage to a voltage-driven switching element having a load between the emitters to drive it, a variable gate resistance circuit connected in series to the gate of the voltage-driven switching element and the load are supplied. Current detecting means for detecting the load current, voltage detecting means for detecting the collector-emitter voltage of the voltage-driven switching element, and a detection signal for the load current detected by the current detecting means. Based on the comparison result of the comparison means and the determination result of the determination means, the comparison means for comparing the reference current value, the determination means for determining whether or not the voltage detected by the voltage detection means is a surge voltage The gist of the invention is that the control means for controlling the resistance value of the variable gate resistance circuit is provided.

[0013]

Therefore, according to the first aspect of the present invention, when the load current supplied to the load changes, the load current is detected by the current detecting means and the detection signal of the load current is preset by the comparing means. The calculated reference current value is compared. Then, an appropriate resistance value for the load current is selected by the control means based on the comparison result, and the resistance value of the variable gate resistance circuit is variably controlled.

According to the second aspect of the present invention, when the load current supplied to the load changes, the load current is detected by the current detecting means, and the detection signal of the load current is preset by the comparing means. The reference current value is compared. On the other hand, the collector detected by the voltage detection means
Whether or not the voltage between the emitters is a surge voltage is determined by the determination means. Then, an appropriate resistance value for the load current is selected by the control means based on the comparison result, and the resistance value of the variable gate resistance circuit is variably controlled. The resistance value of the gate resistance circuit is variably controlled.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) A first embodiment embodying the switching element drive circuit of the present invention will be described in detail below with reference to FIGS.

In the present embodiment, only the parts that are structurally different from the conventional switching element drive circuit shown in FIG. 6 will be described, and the parts that have the same structure as in FIG. Description is omitted.

FIG. 1 shows a switching element drive circuit using an IGBT 1 as a voltage drive type switching element. A variable gate resistance circuit 4 is connected in series between a drive circuit 3 and an element internal gate resistance Rg. There is. I
A current transformer CT as a current detecting means for constantly detecting the load current I ₀ of the load 2 is attached to a part between the collector and the emitter of the GBT 1, and the current transformer CT is connected to the variable gate resistance circuit 4. ing. The collector of the IGBT1
Between the emitters, a voltage detector 5 as a voltage detecting means for constantly detecting the voltage therebetween is connected, and the voltage detector 5 is connected to the variable gate resistance circuit 4. In this embodiment, the load 2 is, for example, a motor whose load current I ₀ changes with time.

Next, the internal structure of the variable gate resistance circuit 4 will be described with reference to FIG. The current transformer CT
Is connected to a load current detection unit 6 in the variable gate resistance circuit 4, and the load current detection unit 6 is the first as a comparison means.
The comparing section 7a, the second comparing section 7b, ..., And the nth comparing section 7z are connected to each other. The comparison units 7a to 7z include
a amp, b amp, ..., z amp (a>b> ...
> Z) reference current values are set respectively. In addition, the R ₁ I ₀ relays 8 are respectively provided corresponding to the comparison units 7a to 7z.
a, R ₂ I ₀ relay 8b, ..., R _n I ₀ relay 8z are connected.

The voltage detector 5 is a variable gate resistance circuit 4
The surge voltage detector 9 and the load current detector 6 are connected to a relay controller 10 as a discriminating means. Further, the relay control unit 10 is connected to the r ₁ V _CE relay 11 a, the r ₂ V _CE relay 11 b, ..., And the r _n V _CE relay 11 z, respectively.

The drive circuit 3 includes a first variable resistor section 1
2 is connected in series, and the first variable resistance section 12 is connected in series to the second variable resistance section 13.
Further, the second variable resistance portion 13 is connected in series to the gate of the IGBT 1.

The first variable resistor section 12 has a plurality of resistors R _{0 to} R _n selected with reference to the manufacturer's recommended gate resistance value.
Are connected in parallel. Further, among the resistors R ₀ to R _n, normally open relay contact 14a~14z are connected in series to the resistor R ₁ to R _n each except resistor R _0. The relay contacts 14a to 14z are connected to the respective R ₁ I
_{The 0} relays 8a to R _n I ₀ are arranged corresponding to the ₀ relays 8z, respectively, and are closed when the relays 8a to 8z are excited.

The second variable resistor section 13 has a plurality of resistors r _{0 to} r _n selected with reference to the manufacturer's recommended gate resistance value.
Are connected in parallel. Further, among the resistors r ₀ ~r _n, the resistor r ₁ ~r _n each except resistor r ₀ normally closed relay contact 15a~15z are connected in series. The relay contacts 15a to 15z have the respective r ₁ V
It is associated arranged to _CE relay 11a~r _n V _CE relay 11z, each of these relays 11a~11z is adapted to open to be excited.

Next, the operation of the switching element drive circuit of the first embodiment constructed as described above will be explained. When a voltage is applied between the gate and emitter of the IGBT 1 from the drive circuit 3, the IGBT 1 is turned on and the load 2 is driven. The current transformer CT always detects the load current I ₀ , and the voltage detector 5 always detects the collector-emitter voltage V _CE regardless of whether or not the load 2 is driven.

Here, when the load current I ₀ becomes large, a detection signal corresponding to the load current I ₀ is input to the load current detection unit 6, and this detection signal is input to all the comparison units 7a to 7z. Then, in each of the comparison units 7a to 7z, a predetermined reference current value is compared with the detection signal. For example, if the detection signal input in the first comparison unit 7a is a
Compare for amperes and above. When the detected signal is larger in the comparison result, the comparison units 7a to 7a
The relays 8a to 8z corresponding to z are excited. Based on the excitation of these relays 8a-8z, the corresponding relay contact 1
4a to 14z are closed.

By this series of operations, the resistances R _{0 to} R _{n are}
Are connected in parallel, the resistance value of the variable gate resistance circuit 4 decreases as the load current I ₀ increases, and the turn-on / turn-off time of the IGBT 1 automatically shortens.

On the other hand, the surge voltage detector 9 causes the voltage V
_{When CE} is detected, the relay controller 10 performs the operation shown in FIG. That is, when the load current detection unit 6 and the surge voltage detection unit 9 detect the load current I ₀ and the collector-emitter voltage V _CE in step (hereinafter, referred to as “S”) 1, in S2, Relay control unit 10 determines whether or not load current I ₀ has changed. When the load current I ₀ has changed, in S4, it is determined whether the voltage V _CE is changed, when the voltage V _CE has changed, in S5, r ₁
The V _CE relay 11a is excited to open the relay contact 15a.
Next, in S6, it is determined whether the voltage V _CE is changed, when the voltage V _CE has changed, in S7, r ₂
The V _CE relay 11b is excited to open the relay contact 15b.
After that, the same operation is sequentially performed up to Sn corresponding to the contacts 7a to 7z, and the process returns to S1.

When the load current I ₀ has not changed in S2, all relay contacts 15a to 15z are closed in S3, and the process returns to S1. Also, S4, S
6, ..., If there is no change in the voltage V _CE , S1
Return to.

By this series of operations, the resistances r _{0 to} r _{n are}
Are connected in parallel, the resistance value of the variable gate resistance circuit 4 increases when a surge voltage is detected.
The surge voltage between the collector and the emitter of the IGBT 1 is suppressed.

Therefore, in this embodiment, the load current I
_{Since both 0} and collector-emitter voltage V _CE are constantly detected and the resistance value of the variable gate resistance circuit 4 is set to an appropriate value, the turn-on / turn-off time can be shortened. At the same time, it is possible to prevent damage to the IGBT 1 due to an excessive surge voltage. (Second Embodiment) A second embodiment of the switching element drive circuit according to the present invention will be described in detail below with reference to FIGS.

In the second embodiment, as shown in FIGS.
Only parts different in structure from the switching element drive circuit of the first embodiment shown in FIG. 2 will be described, and parts having the same structures as those in FIGS. 1 to 3 will be assigned the same reference numerals and detailed description thereof will be omitted.

FIG. 4 shows a switching element drive circuit using the IGBT 1 as a voltage drive type switching element, and a variable gate resistor 20 as a variable gate resistance circuit is provided between the drive circuit 3 and the element internal gate resistance Rg.
Are connected in series. The current transformer CT and the voltage detector 5 are connected to a control device 21 as a comparison means, a discrimination means and a control means, respectively, and the control device 21 is connected to the variable gate resistor 20.

Next, the internal configuration of the control device 21 will be described with reference to FIG. 5. The current transformer CT and the voltage detector 5 are the central processing unit (hereinafter referred to as CPU) built in the control device 21. ) 22 is connected. Also,
The CPU 22 includes a read-only memory (hereinafter referred to as ROM) 23, and is a program for controlling the writing of detection signals from the current transformer CT and the voltage detector 5 to a RAM described later,
A program for comparing and controlling the detection signal read from the current transformer CT with a prestored reference current value, a program for determining and controlling whether the voltage V _CE read from the voltage detector 5 is a surge voltage, and a variable A control program of the gate resistor 20 and the like are stored. Further, the CPU 22 is a readable / writable memory (hereinafter referred to as RAM) 24.
The CPU 22 writes and reads data and the like necessary for arithmetic processing. The RAM 24 also includes a storage area (not shown) that stores the detection signals from the current transformer CT and the voltage detector 5.

When a detection signal corresponding to the load current I ₀ is input to the CPU 22, the CPU 22 compares it with a reference current value stored in advance and, based on the comparison result, the IGB.
The resistance value that shortens the turn-on / turn-off time of T1 is calculated. Then, the CPU 22 uses the variable gate resistor 2
Variable control is performed so that 0 is the calculated resistance value.

On the other hand, the detection signal corresponding to the voltage V _CE is CP
When the CPU 22 determines that the detection signal is a surge voltage and is input to U22, the CPU 22 gradually increases the resistance value of the variable gate resistor 20 until the surge voltage is no longer generated.

Therefore, also in the second embodiment, both the load current I ₀ and the collector-emitter voltage V _CE are constantly detected so that the resistance value of the variable gate resistor 20 becomes an appropriate value. Since it is configured, the turn-on / turn-off time can be shortened and damage to the IGBT 1 due to an excessive surge voltage can be prevented.

The present invention is not limited to the above-mentioned embodiments, but may be modified as follows without departing from the spirit of the present invention. (1) Instead of the IGBT 1, another voltage control type switching element may be used. (2) The voltage detector 5 may be omitted and the resistance value of the variable gate resistance circuit may be changed only by changing the load current I ₀ . Even in this case, the IGBT 1 is automatically
Turn-on and turn-off time of
The surge voltage generated between the collector and the emitter of the IGBT 1 can also be reduced to some extent.

[0037]

As described above in detail, according to the first invention, even if the load current of the load provided between the collector and the emitter in the voltage controlled switching element is changed,
Since the resistance on the gate side of the voltage controlled switching element automatically becomes the optimum resistance value, it is possible to omit the work of selecting and replacing the external gate resistance.

According to the second invention, in addition to the effect of the first invention, there is an excellent effect that damage to the voltage-driven switching element can be prevented in advance.

[Brief description of drawings]

FIG. 1 is a circuit diagram of a switching element drive circuit showing a first embodiment embodying the present invention.

FIG. 2 is a block diagram of a variable gate resistance circuit similarly showing the first embodiment.

FIG. 3 is a flowchart which similarly describes the first embodiment.

FIG. 4 is a circuit diagram of a switching element drive circuit showing a second embodiment of the present invention.

FIG. 5 is a block diagram of a control device similarly showing a second embodiment.

FIG. 6 is a circuit diagram showing a conventional switching element drive circuit.

[Explanation of symbols]

1 ... IGBT as voltage drive type switching element, 2
... load, 4 ... variable gate resistance circuit, 5 ... voltage detector as voltage detecting means, 7a to 7z ... first as comparing means
-Nth comparator, 10 ... Relay control section as discrimination means,
20 ... A variable gate resistor as a variable gate resistor circuit,
21 ... Control device as comparing means, discriminating means and control means, I ₀ ... Load current, CT ... Current transformer as current detecting means.

Claims (2)

[Claims] 1. A switching element drive circuit for applying a voltage to a voltage drive type switching element having a load provided between a collector and an emitter to drive the voltage drive type switching element, wherein a variable gate resistor connected in series to the gate of the voltage drive type switching element. A circuit, a current detection means for detecting a load current supplied to the load, a comparison means for comparing a detection signal of the load current detected by the current detection means and a preset reference current value, the current A switching element drive circuit comprising: a control unit that controls a resistance value of the variable gate resistance circuit based on a comparison result of the value comparison unit. 2. A switching element drive circuit for driving by applying a voltage to a voltage drive type switching element having a load provided between a collector and an emitter, wherein a variable gate resistor connected in series to the gate of the voltage drive type switching element. A circuit, a current detecting means for detecting a load current supplied to the load, a voltage detecting means for detecting a collector-emitter voltage of the voltage-driven switching element, and a load current detected by the current detecting means. Comparing means for comparing the detection signal and the preset reference current value, determining means for determining whether or not the voltage detected by the voltage detecting means is a surge voltage, comparison results of the comparing means, and And a control means for controlling the resistance value of the variable gate resistance circuit based on the discrimination result of the discrimination means. Circuit for driving a switching element.