Drive circuit for power device

Details Drive circuit for power device Drive circuit for power device

1999-04-10

2001-04-10

Sherry, Michael J. (Department: 2836)

Electricity: electrical systems and devices

Safety and protection of systems and devices

With specific current responsive fault sensor

C361S093100, C327S310000

Reexamination Certificate

active

06215634

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to drive circuits for power devices, and in particular to drive circuits for power devices that prevent protection circuits for monitoring operating states of the power devices, from performing unstable operations due to influences of inductances present in wires connecting the drive circuits with the power devices.
BACKGROUND OF THE INVENTION
In conventional large-capacity inverters for driving industrial motors, thyristors that can easily provide a high breakdown voltage and allow flow of large current were used as switching devices. In middle- or small-capacity inverters, bipolar junction transistors were mainly used as switching devices. Later, IGBT (Insulated Gate Bipolar Transistor) has been used which exhibits both a high input impedance characteristic peculiar to MOSFET (Metal Oxide Semiconductor Field Effect Transistor) and a low saturation-voltage characteristic peculiar to bipolar transistors. In recent years, the IGBT has been developed so as to provide a higher breakdown voltage and a larger current capacity, and are now employed in the field of thyristors. Because of a high current value to be handled by the IGBT, it is essential to protect the IGBT against overcurrent and overheat. Generally, drive circuits for driving these power devices are provided with overcurrent protection and overheat protection functions.
FIG. 5
is a circuit diagram showing a known drive circuit for an IGBT, which incorporates protection networks. In
FIG. 5
, an IGBT chip
100
, a flywheel diode
200
and a drive circuit
300
are illustrated. The IGBT chip
100
principally consists of an IGBT
101
, and a temperature detection diode
102
that is embedded in the chip and serves as a temperature sensor for detecting the junction temperature of the IGBT
101
. The collector of the IGBT
101
is connected to the cathode of the flywheel diode
200
, and the emitter is connected to the anode of the flywheel diode
200
.
The drive circuit
300
includes a gate control unit
301
that is connected to the gate of the IGBT
101
and serves to control turn-on and turn-off of the IGBT
101
, a comparator
302
for determining overcurrent or excess current of the IGBT
101
, and a comparator
303
for determining excessively high temperature or overheat of the device. The comparator
302
has a non-inverting input terminal to which a junction between the sense emitter of the IGBT
101
and a resistor
304
is connected, and an inverting input terminal to which a reference voltage source
305
is connected. The comparator
303
has a non-inverting input terminal to which a reference voltage source
306
is connected, and an inverting input terminal to which a junction between a constant-current source
307
and the anode of the temperature detection diode
102
is connected.
The emitter of the IGBT
101
, cathode of the temperature detection diode
102
, negative terminals of the reference voltage sources
305
,
306
, and the resistor
304
are connected to the ground terminal (GND) of the drive circuit
300
. An inductance L
101
between the constant-current source
307
and the temperature detection diode
102
, inductance L
102
between the gate control unit
301
and the gate terminal of the IGBT
101
, inductance L
103
between the sense emitter of the IGBT
101
and the comparator
302
, inductances L
104
, L
105
, L
106
, L
107
on the ground GND represent inductances of internal wires.
In an overcurrent protection circuit of the IGBT
101
, part of the emitter current of the IGBT
101
is taken out from the sense emitter, so that the sense emitter current flows through the resistor
304
. The comparator
302
compares the terminal voltage that is produced across the resistor
304
due to the sense emitter current, with the voltage of the reference voltage source
305
, and determines that overcurrent flows through the IGBT
101
when the terminal voltage of the resistor
304
due to the sense emitter current becomes higher than the voltage of the reference voltage source
305
. In an overheat protection circuit of the IGBT
101
, on the other hand, the comparator
303
compares the forward voltage of the temperature detection diode
102
through which a constant current flows from the constant-current source
307
, with the voltage of the reference voltage source
306
, and determines that the IGBT
101
is overheated when the forward voltage of the temperature detection diode
102
becomes lower than the voltage of the reference voltage source
306
.
The IGBT
101
is turned on or off under control of the gate control unit
301
of the drive circuit
300
. The portion of the IGBT
101
between the gate and the emitter behaves like a capacitor. Upon turn-on of the IGBT
101
, therefore, the drive current charges the capacitor between the gate and the emitter, and flows from the gate to a negative terminal of a power supply (not shown), through the emitter and the ground GND. Upon turn-off, the charge stored between the gate and the emitter is discharged, and the discharge current flows from the gate to the emitter of the IGBT
101
, through the gate control unit
301
and the ground GND. The drive current that flows upon turn-on and turn-off of the IGBT
101
is transient, and has a considerably large value on the order of ampere (A).
A plurality of sets or combinations each consisting of the drive circuit
300
, IGBT
100
and the flywheel diode
200
as described above may be arranged in parallel with each other, along with a single direct-current power supply. In the case of a bridge circuit that use N-channel power devices to provide a polyphase inverter, for example, circuits for driving negative-side power devices may use a common direct-current power supply. In the case of a bridge circuit that use P-channel power devices to provide a polyphase inverter, circuits for driving positive-side power devices may use a common direct-current power supply. The following example illustrates two drive circuits corresponding to two phases on the negative side of a bridge circuit that uses N-channel power devices to provide a three-phase inverter.
FIG. 6
is a view showing an example of connection of two drive circuits that share a single power supply. In
FIG. 6
, the same reference numerals as used in
FIG. 5
are used for identifying the corresponding constituent elements, of which no detailed description will be provided. For the sake of brevity, the circuits for overcurrent protection and overheat protection are not illustrated in
FIG. 6
nor explained in the following description.
The gate of the IGBT
101
is connected to the drive circuit
300
, and the collector is connected to a load terminal V, while the emitter is connected to a load terminal N. In internal wires through which the main current of the IGBT
101
flows between the load terminal V and the load terminal N, an inductance
108
exists on the side of the collector of the IGBT
101
, and an interphase inductance
109
exists between the emitter of the IGBT
101
and the emitter of the adjacent IGBT
101
a
, while an inductance L
110
exists between the emitter of the IGBT
101
a
and the load terminal N. The drive circuit
300
is connected to the positive and negative terminals of a dc power supply
400
, and inductances L
104
, L
105
, L
106
, L
107
exist in an internal wire that extends from the ground GND to the negative terminal of the dc power supply
400
. Similarly, IGBT
101
a
and drive circuit
300
a
are provided in the circuit for another phase as shown in the lower part of
FIG. 6
, and the same dc power supply
400
as used for the drive circuit
300
is connected to the drive circuit
300
a
. Also, inductances L
104
a
, L
105
a
, L
106
a
, and L
107
a
exist in an internal wire on the ground GND of the drive circuit
300
a.
When the upper drive circuit
300
supplies drive current to the IGBT
101
, the IGBT
101
is turned on, and load current I
ON
flows from the load terminal V to the load terminal N, through the inductances L
108
, IGBT
101
, and

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