JP3325303B2 - Switch device with protection function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a switch device using a voltage-driven power transistor, and more particularly to a switch device having a protection function of detecting an overcurrent due to a short circuit or the like at a high speed and limiting the current.

[0002]

2. Description of the Related Art As a voltage-driven power transistor, I
GBT (Insulated Gate Bipolar Transiston) is widely known. Since the IGBT has a low on-voltage, a MOS gate structure, a small driving power, and a relatively high-speed switching, the application field is rapidly expanding.
The characteristics of on-voltage and switching speed are in conflict,
Research is being conducted day and night to improve the trade-off and achieve higher performance devices.

[0005] The characteristic C in FIG. 5A is the on-voltage characteristic of the third and subsequent generation IGBTs predicted from these studies.
This is shown in comparison with the on-voltage characteristic A of the first generation IGBT. Current IGBTs are shown in characteristic B in the second generation. Incidentally, the collector current I _c are respectively shown as a percentage of the rated current of the IGBT 100.

[0004] As is apparent from these characteristics, when the collector-emitter voltage V _CE rises a load short circuit or the like flows several times the collector current I _c of the rated current, the first generation of IG
Overcurrent flows 6 to 8 times in the BT and 10 to 12 times in the second generation IGBT.

[0005] In the IGBTs of the third and subsequent generations, which are currently under study, a pattern of the order of μm of a DRAM class and other improvements are applied, so that an overcurrent of more than ten times as shown by the characteristic C flows. When such a large overcurrent occurs, there is a problem that it is difficult to cut off the current at high speed, and it becomes difficult to protect the element from overcurrent. Hereinafter, protection of a conventional IGBT when a load is short-circuited will be described.

FIG. 5B shows a general main circuit configuration using an IGBT. This device drives a motor 3 by converting a DC voltage of a DC voltage source 1 into an AC voltage by a bridge type converter (inverter) including IGBTs 21 to 26. In such a device, when a short circuit occurs between terminals on the load (motor) side, a short circuit current flows through the positive and negative IGBTs. Also, the positive and negative IGs of the same arm
Similarly, when an ON signal (a signal due to noise or malfunction) is input to the BT, a short-circuit current also flows.

The short-circuit withstand capability of an IGBT capable of withstanding such a short-circuit state is 80% of the element rated voltage in the current IGBT.
Time of 10 to 20 μs at a voltage of 7.5 to 10 μs
Short-circuit protection that detects overcurrent within the current limit and shuts off the current is performed.

[0008] Figure 6 is a characteristic diagram of a short-circuit tolerance showing the relationship between collector-emitter voltage V _CE certain lower flows during a short circuit the collector current I _c and tolerance time (t _1), shows the test circuit with It is a thing. I _c and t ₁ As is apparent from this characteristic has a substantially constant power relation, the collector current I _c by a load short-circuit or the like is increased tolerance time t
₁ becomes short and requires high-speed protection operation.

Therefore, various methods have been proposed to reduce the gate voltage of the IGBT and to limit the short-circuit current by utilizing the transistor function of the IGBT when an overcurrent due to a load short-circuit or the like is detected, and to lengthen the apparent short-circuit withstand time (Japanese Patent Application No. H10-163191). 60-92870,
Japanese Patent Application No. 3-171484).

The circuit shown in FIG. 7 (a) is a circuit which was announced at an academic meeting (National Institute of Electrical Engineers of Japan 470) and is a main IGBT.
4a, a current sense IGBT 4b for detecting the current of 4a is provided;
When the current exceeds a specific current, the NLU circuit 50 lowers the gate voltage of the IGBT to suppress the short-circuit current.

As shown in FIG. 7D, the NLU circuit 50
When the voltage drop of the resistor 52 due to the emitter current of the current sense IGBT 4b exceeds the gate threshold voltage of the MOSFET 54, a current flows through the drain of the MOSFET 54 via the gate resistor 51 and acts to reduce the gate voltage of the IGBT. Also, the NLU circuit 50 may be a circuit shown in FIG. 7E, in which the MOSFET 54 is replaced with a bipolar transistor 55.

When such a circuit is constructed, I
By reducing the gate voltage of the GBT and increasing the on-resistance of the IGBT, the short-circuit current can be limited as shown in FIG. 7C, and the short-circuit withstand time can be made apparently long as shown in FIG. 7B. it can.

[0013]

The conventional method of FIG. 7 has increased the short-circuit withstand capability of the IGBT module, but has the following problems. That is, since the short-circuit current is limited to about 200%, it is difficult to detect a short-circuit accident by detecting overcurrent.

[0014] Another short-circuit fault detection circuit must be added to the circuit to turn off the driving signals by such circuits, such as to detect that V _CE of the IGBT remains high added-on signal is complex Become.

FIG. 7 shows the value Rg of the gate resistor 51.
Since the gate voltage is different even if the drain current of the FET 54 is the same, the current limit value _ICL changes according to the magnitude of Rg as shown in FIG. Therefore, short-circuit current limit value by decreasing Rg I _CL increases short-circuit tolerance time for fast switching of the IGBT has drawbacks shortened.

Further, there is a problem that oscillation occurs when IGBTs are connected in parallel. That is, when there is a difference in the operation level of the current limiting function of each IGBT module, when the current limiting function of one IGBT operates, the limited current is transferred to another IGBT, and the current limiting function of the IGBT operates. . By repeating this, a kind of oscillation state is generated and IGB
There is a risk that T is deteriorated.

Although the operation of the current limiting function of the IGBT of the circuit shown in FIG.
When the diodes are used in anti-parallel connection, the following problems occur. That is, as shown in the circuit of FIG.
When turning on the IGBT24 when flowing a current I _c of the IGBT24 as shown in the waveform diagram of Figure 9 flows peak current 1.5 to 2 times the load current iD the rising portion. The hatched portion of this current waveform is the recovery current of the diode 21D, which increases as the withstand voltage of the diode increases, and has a characteristic that increases as the temperature rises. If the current limit value is lower than this peak current, the turn-on loss of the IGBT increases significantly. For this reason, assuming that the iD is used up to the rated current of the IGBT, the peak current is about 200%, and the current limit value needs to be set to at least 250% or more in view of the margin. . Further, if Rg is reduced in order to increase the switching speed, the current limit value may be about 500 to 600%.

The present invention has been made under the above-mentioned technical background, and an object of the present invention is to detect an overcurrent of a transistor having a small on-voltage and a large short-circuit current at a high speed to cut off current limiting. And a switch device having a highly reliable protection function.

[0019]

In order to achieve the above object, the present invention provides the following means.

[0020]

(1) Main current is controlled according to drive voltage
And a parallel connection to the transistor
And a current detector for outputting a detection voltage corresponding to the main current.
The detection voltage is equal to a set voltage.
Outputs a control signal proportional to the detection voltage in the range exceeding
Level detecting means for detecting the set voltage, and
Means for adjusting the short-circuit withstand capability that decreases with increasing temperature of the
Adjusting the drive voltage according to the control signal to adjust the main current
Current control means for limiting and controlling the
An abnormal signal is output when the alarm signal is
When the drive voltage is continuously output, the drive voltage is controlled to the off state.
Drive command control means for setting the main current to zero.

(2) Main current is controlled according to drive voltage
And a parallel connection to the transistor
And a current detector for outputting a detection voltage corresponding to the main current.
The detection voltage is equal to a set voltage.
Outputs a control signal proportional to the detection voltage in the range exceeding
Level detecting means for detecting the drive electric power according to the control signal.
Current control means for regulating the main current by regulating the pressure
And the control signal is output continuously for a first predetermined time.
When the drive voltage is gradually increased toward a value slightly higher than zero.
A current interrupting means for decreasing the current and the control signal
Output for a second predetermined time longer than the predetermined time
When the drive voltage is turned off,
Control means are provided.

[0023]

[0024]

[0025]

[Action] (1) When the main current flows through the transistor, the current
The detection means outputs a detection voltage proportional to the main current. this
If the detection voltage exceeds the voltage set by the level detection means,
A control signal proportional to the difference value is output. At this time,
The set voltage decreases as the transistor temperature rises.
Setting lowers the current limit and lowers the temperature.
Even if it rises, reliable overcurrent protection can be performed.

(2) When an overcurrent flows through the transistor and the current limiting operation continues for a predetermined time, a control signal is continuously output from the level detecting means for a predetermined time. At this time, the current cutoff means gradually reduces the drive voltage to a value slightly higher than zero to make the main current zero, so that the overcurrent is cut off while suppressing the surge voltage and the overvoltage of the transistor is reduced. Protection can be performed at the same time .

[0027]

FIG. 1 shows an embodiment of the present invention.

In FIG. 1A, an IGBT 4 includes an IGBT 4a for controlling a main current and a sense IGBT 4 for detecting a current.
4b, each gate and collector are connected in parallel, and each emitter is an independent terminal. AND circuit 11 turns on and off the transistor 12 in response to the drive signal S _0. The photocoupler 13 turns on the transistor 12
With a phototransistor that operates with a gate power supply 19, 20 that is insulated when a current flows through the light emitting diode when turned off,
The transistors 14 and 15 connected in a complementary manner are turned on / off in accordance with the turning on / off of the transistor 12. Its output voltage is complementarily connected to transistors 17, 18 via a series circuit of a resistor 16 and a resistor 34 and a capacitor 35.
Of the output voltage V _G
Is used as the drive voltage of the IGBT via the resistor 51 and the IGBT 4
a, 4b are added to the gates. Transistor 55, current starts to flow to the base when the voltage drop across the resistor 52 due to the emitter current I ₁ of the sense IGBT4b exceeds the threshold voltage between the base and emitter, in proportion to the deviation value as shown in FIG. 1 (b) current I ₂ flows through the collector. This current I ₂ is supplied to the complementary connected transistor 1
It flows from the base voltages 7 and 18 via the resistor 36, the photocoupler 32, and the diode 31. Photocoupler 32 has a photo-transistor operating in control power supply which is insulated when the current I ₂ flows, and outputs an abnormality signal EG. The timer 33 always outputs a signal LK of "1". When the abnormal signal EG is continuously output for a predetermined time, the timer 33 times out and the output signal L
K is set to “0”.

In the above configuration, the drive command S ₀ is “1”.
Then, the transistor 12 is turned on by the output of the AND circuit 11, and the transistor 14 complementally connected via the photocoupler 13 is turned on. This allows gate power
The voltage of 19 is applied to the gates of the transistors 17 and 18 connected in a complementary manner through a series circuit of the resistor 16 and the resistor 34 and the capacitor 35, and the power is amplified and the IGB is
The IGBTs 4a and 4b are both turned on by being applied to the gates of T4a and 4b. When the drive command S ₀ becomes “0”,
The transistor 12 is turned off, the transistor 14 is turned off by the output of the photocoupler 13, the transistor 15 is turned on, the transistor 17 is turned off, the transistor 18 is turned on, and the IGBT is turned on.
A negative bias voltage is applied to the gates of
T4a and 4b are both turned off. In this case, the resistor 34 and the capacitor 35 act as a lead circuit and act to change the gate voltage at high speed.

When the drive command S ₀ is “1”, the IGBT 4
When a, 4b is turned on, an overcurrent flows to the IGBT 4 a, the emitter current I ₁ of IGBT4b Figure 1
(B) to indicate a point to the collector of the over transistor 55 (the base-emitter threshold voltage of transistor 55) is a current I ₂ flows. From the voltage drop of the resistor 16 due to the current I _{2, the} complementary connected transistor 17,
The gate voltage of the IGBTs 4a and 4b is reduced.

FIG. 2A is a characteristic diagram of the IGBT, in which the collector-emitter voltage V _{CE is set} with the gate voltage as a parameter _.
And is a diagram showing the relationship between the collector current I _c. As shown in this figure, the collector current of the IGBT changes in accordance with the gate voltage, and the IGBT is normally turned on with a large gate voltage in order to reduce the ON voltage, so that a large overcurrent flows when a load short circuit or the like occurs.

However, in this embodiment, as described above,
When an overcurrent flows through the GBT, the gate voltages of the IGBTs 4a and 4b decrease, the ON voltage of the IGBT 4a increases, and the overcurrent is suppressed within a predetermined range.

In FIG. 1 (b), the current I _{2 for} reducing the current of the IGBT 4a to the gate voltage at which the current limit value is reached.
Was a I _2L, current I ₁ by the current control loop when the current I ₁ of IGBT4b passing a current of I _2L and b point b
It is controlled to be kept at the point.

When the current limiting operation is started as described above, the abnormal signal EG is output from the photocoupler 32 by the current _I2L , whereby the timer 33 starts time counting. When the current limiting operation is continuously performed for a predetermined time, the timer 33 counts up and sets the output signal LK to “0”,
Also driving command S ₀ Close gate of the AND circuit 11 is in a state of "1" to force off the transistor 12. As a result, the gate voltages of the IGBTs 4a and 4b are negatively biased, and the overcurrent is cut off.

[0035] FIG. 2 (b) is a diagram load is a time chart in the case of a "1" to drive command S ₀ in a state of being short-circuited. At time t ₁ S ₀ is "0" to "1" becomes the gate voltage V _G is varied from negative to positive IGBT4
When a and 4b are turned on, a short-circuit current starts flowing in the IGBT 4a, and the emitter current I ₁ of the IGBT 4b rises rapidly, and a current I ₂ flows to the collector of the transistor 55 to start a current limiting operation. The gate voltage V _G by the current limiting operation current I ₁ is controlled to a low value at time t ₂ is controlled to a predetermined value. Gate voltage V _G this state becomes "0" from "1" output signal LK of timer 33 at time t ₃ continuously for a predetermined time is returned to a negative IGBT 4 a, 4b of the current becomes zero current I ₁ Becomes zero.

When performing the current limiting operation, the resistor 34 and the capacitor 35 act as a delay circuit, and the transistor 55
The gain (ΔI ₂ / ΔI ₁ ) of FIG.
When the interval between −b and −b is narrowed, oscillation is prevented, a stable operation is performed, and the gate voltage V _G as shown in FIG.
Carry out the action to delay the time t ₂ to drop in. This delay circuit and the gate resistor 51 and the IGBT 4 a, the current I ₁ by the action of the delay circuit due to the capacitance between 4b of the gate-emitter overshoots until the current limit is reached. This overshoot current I ₁ has a beneficial effect when applying the IGBT to an actual circuit. That is, the circuit compensates for the increase (shaded area) caused by the recovery current flowing through the diode 21D in the circuit of FIG. As described above, in this embodiment, the current limit value can be set low by actively utilizing the overshoot of the current limit control system. When the recovery current of the diode connected in anti-parallel with the IGBT is small, the resistor 34 and the capacitor 35 in FIG. 1 can be omitted.

FIG. 3A shows a relationship between the temperature _{Tc of} the IGBT and the short-circuit withstand time t, and the higher the temperature, the shorter the withstand time. For example, when T _c is 125 ° C., the withstand time is reduced by almost half compared to the case of 25 ° C.

Therefore, utilizing the characteristic that the threshold voltage of the transistor 55 decreases with the temperature, the bipolar transistor 55 is placed in a place close to the temperature of the IGBT (for example, a bonding part of the emitter is desirable, but an insulating pad part slightly separated may be used). By arranging, as shown in FIG. 3B, the short-circuit current (current limit value) can be reduced as the temperature of the IGBT rises, and the apparent short-circuit withstand time can be extended. FIG. 3C shows a MOSF as the transistor 55.
This shows a case where ET is used, and the current is constant without being affected by temperature. However, even in this case, it is possible to arrange the resistor 52 at a location close to the temperature of the IGBT and use a resistor having a positive temperature coefficient to obtain the characteristic shown in FIG.

When the IGBT 4a and the IGBT 4b are formed of different chips, the gate voltage of the IGBT 4b is reduced by the voltage drop of the resistor 52, and the IGBT 4b is turned off.
In some cases, a proportional relationship between the main current flowing through the a and the detection current flowing through the IGBT 4b cannot be obtained. In such a case, I
The threshold voltage of the gate of the GBT 4b may be set lower by an amount corresponding to the voltage drop of the resistor 52 when the current limit operates, so that a proportional relationship between the main current and the detected current is established in a range where the current limit operates. Good. FIG. 4 shows a second embodiment of the present invention. FIG. 4A is a diagram showing a configuration of a main part, and FIG. 4B is a waveform diagram for explaining the operation.

The gate voltage V _G at time t ₁ the drive command is given in a state in which the load is short-circuited of the IGBT becomes positive when the short-circuit current flows in the IGBT from the negative, the detected current I ₁ flows in proportion to the short-circuit current. This allows transistor 55
Diode 31 to the collector of the time t ₂ the voltage drop in the resistor 16 flows through current I ₂ through the zener diode 44 is generated
In the gate voltage V _G is reduced to suppress value circuit current to the current limit value. Further, a current flows through the resistors 37 and 38, and simultaneously with the start of the current limiting operation, the transistor 39 is turned on to start the time count of the time delay circuit 40. At time t ₃ after a lapse of a predetermined time, the control signal c is output from the time delay circuit 40, and a positive voltage is applied to the gate of the MOSFET 43 via the resistor 41. Capacitor 42 to the gate of the MOSFET43 is provided, the gate voltage thereof at the rising time t ₄ with a delay MOSFET43 gradually begins to conduct, gradually the gate voltage V _G of the IGBT to稍高have values from zero Lower. Thus IGBT current gradually decreases and becomes zero the detected current I ₁ also becomes gradually reduced to zero as shown. Photocoupler 32 is MO
It operates by the current flowing through the SFET 43 and outputs an abnormal signal EG. Gate voltage V _G at time t ₅ stops the output of the drive command by the signal EG is negatively biased. According to the second embodiment, since the overcurrent continuously flows for a predetermined time and then gradually decreases, the surge voltage can be set to a low value. Note that the zener diode 44 limits the gate voltage so as not to be excessively lowered, and may be replaced with a resistor or omitted. The delay circuit for adjusting the overshoot amount is a transistor 55.
An amplification circuit or the like can be provided at the subsequent stage and added to that part.

The present invention also relates to IGBTs 4a and 4b,
One level detector consisting of transistor 55 and resistors 52 and 56
By configuring as an IGBT module housed in one package, an easy-to-use switch device with a large degree of freedom in the main circuit configuration can be provided. That is, when the IGBT modules are connected in parallel and used, the gate signals of all the IGBTs connected in parallel can be suppressed by the output signal of the level detection section that operates fastest, and overcurrent protection can be performed. Thus, overcurrent protection can be easily performed.

[0042]

According to the switch device having the protection function of the present invention, the set voltage of the level detecting means is set to the level of the transistor.
By setting it to decrease as the temperature rises,
Even if the current limit value decreases and the temperature rises, reliable overcurrent
Protection.

Further , the current cutoff means reduces the drive voltage to zero.
To a slightly higher value to reduce the main current to zero.
The surge voltage when interrupting the overcurrent.
More reliable protection device
A switch device having a function can be provided.

[Brief description of the drawings]

FIG. 1 shows a first example of a switch device having a protection function according to the present invention.
FIG. 4A is a diagram showing an embodiment, in which FIG.

FIGS. 2A and 2B are diagrams for explaining the operation of the first embodiment, wherein FIG. 2A is a characteristic diagram of an IGBT and FIG.

3A and 3B are diagrams for explaining another operation of the first embodiment, wherein FIG. 3A is a characteristic diagram of the IGBT, and FIGS. 3B and 3C are current waveform diagrams.

FIGS. 4A and 4B are diagrams showing a second embodiment of the present invention, wherein FIG. 4A is a main part configuration diagram, and FIG.

5A and 5B are diagrams for explaining the technical background, and FIG.
The characteristic diagram (b) of the BT is a general main circuit configuration diagram in which the IGBT is used.

FIG. 6 is a characteristic diagram showing a withstand time with respect to an overcurrent of the IGBT, and also shows a test circuit thereof.

7A and 7B are diagrams showing a conventional IGBT having an overcurrent protection function, in which FIG. 7A is a main part configuration diagram, FIG. 7B is a load short-circuit tolerance distribution diagram, FIG. 7C is a load short-circuit test waveform diagram, and FIG. ) Is the main part (N
LU)

FIG. 8 is a characteristic diagram for explaining a problem of the conventional configuration.

FIG. 9 is a diagram showing a main circuit main part configuration diagram and an operation waveform diagram for explaining a problem in operation of a main circuit using an IGBT;

[Explanation of symbols]

4 IGBT, 4a Main IGBT, 4b Sense IGB
T, 11 ... AND circuit, 12, 14, 15, 17, 18, 39, 55 ... Transistor, 13, 32 ... Photocoupler, 16, 34, 36, 37, 38, 41, 51, 5
2,56 ... resistance, 19, 20 ... gate power supply, 31 ... diode, 33
... Timer, 35 ... Capacitor, 43 ... MOSFET, 44 ...
Zener diode.

────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Makoto Hideshima 1, Komukai Toshiba-cho, Saiwai-ku, Kawasaki-shi, Kanagawa Prefecture Inside the Tamagawa Plant, Toshiba Corporation (56) References JP-A-3-207214 (JP, A) JP-A-3-207214 JP-A-62-229757 (JP, A) JP-A-2-226808 (JP, A) JP-A-4-96618 (JP, A) JP-A-4-236122 (JP, A) JP-A-3-183209 (JP , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02H 3/08-3/253

Claims (2)

(57) [Claims] A transistor capable of having 1. A controls the main current in response to the drive voltage, the device having a current detecting means connected in parallel to the transistor and outputs a detection voltage corresponding to said main current, said detector Level detection means for outputting a control signal proportional to the detection voltage in a range where the voltage exceeds a set voltage; and
Short-circuit withstand voltage adjusting means for decreasing with increasing temperature, current control means for controlling the main voltage by controlling the drive voltage by the control signal, and an abnormal signal when the control signal is output And a drive command control means for controlling the drive voltage to be in an off state and making the main current zero when the abnormal signal is continuously output for a predetermined time. Switch device. 2. The method of controlling a main current according to a drive voltage.
And a parallel-connected transistor
Current detection means for outputting a detection voltage corresponding to the main current.
In a device having a step, the detection voltage exceeds a set voltage.
Output a control signal proportional to the detection voltage within the range
Level detection means, and the drive voltage is controlled by the control signal.
Current control means for regulating and controlling the main current;
When the control signal is continuously output for a first predetermined time,
The drive voltage is gradually lowered toward a value slightly higher than zero.
Current interrupting means to be turned off, and the control signal
Output for a second predetermined time longer than the predetermined time
A drive command control means for controlling the drive voltage to an off state.
Switch with protection function characterized by the provision of steps
Switch.