Active solid-state devices (e.g. – transistors – solid-state diode – Field effect device – Having insulated electrode
Reexamination Certificate
2002-04-17
2004-06-29
Flynn, Nathan J. (Department: 2826)
Active solid-state devices (e.g., transistors, solid-state diode
Field effect device
Having insulated electrode
C257S068000, C257S300000, C327S379000, C327S380000, C327S381000, C327S360000, C327S374000, C327S198000, C327S108000
Reexamination Certificate
active
06756623
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device which charges and discharges gate input capacitance of an insulated gate transistor and a method of driving the transistor.
2. Description of the Background Art
FIG. 14
is a view showing a configuration of a semiconductor device in a first background art. As shown in
FIG. 14
, the semiconductor device of the first background art comprises an IGBT (Insulated Gate Bipolar Transistor)
7
which is an insulated gate transistor, a protection diode
8
working against a reverse voltage applied between an emitter and a collector of the IGBT
7
, a gate driving circuit
3
, a control power supply
15
a
which outputs a voltage of +15 V, a control power supply
15
b
which outputs a voltage of −15 V, a transistor
4
a
having a collector connected to the control power supply
15
a
, a transistor
4
b
having an emitter connected to the control power supply
15
b
and a resistor
5
. Gate input capacitance
6
is parasitic capacitance generated structurally between a gate and the emitter of the IGBT
7
.
In the semiconductor device of
FIG. 14
, in order to turn the IGBT
7
on, first, the gate driving circuit
3
turns the transistor
4
a
on and turns the transistor
4
b
off. When the transistor
4
a
is turned on, the control power supply
15
a
supplies the gate of the IGBT
7
with the voltage of +15 V. At this time, since the gate input capacitance
6
is present between the gate and emitter of the IGBT
7
, electric charges are supplied by the control power supply
15
a
to the gate input capacitance
6
, thereby producing a gate current. As the gate input capacitance
6
is being charged, a gate voltage of the IGBT
7
increases and the IGBT
7
is turned on when the gate voltage of the IGBT
7
reaches a threshold voltage or more. After that, the charge of the gate input capacitance
6
of the IGBT
7
is completed, the gate voltage becomes about +15 V and the gate current almost stops flowing therein. Further, in some cases, the gate current flowing during a period from the start to end of the charge of the gate input capacitance
6
is simply referred to as “charging current”.
When the IGBT
7
is turned off, the gate driving circuit
3
turns the transistor
4
a
off and turns the transistor
4
b
on. When the transistor
4
b
is turned on, the control power supply
15
b
supplies the gate of the IGBT
7
with the voltage of −15 V. At this time, since the electric charges are accumulated in the gate input capacitance
6
of the IGBT
7
, the electric charges are extracted by the control power supply
15
b
, thereby producing the gate current in a direction reverse to that of the case where the IGBT
7
is turned on. As the gate input capacitance
6
is being discharged, the gate voltage of the IGBT
7
decreases and the IGBT
7
is turned off when the gate voltage of the IGBT
7
becomes less than the threshold voltage. After that, the discharge of the gate input capacitance
6
of the IGBT
7
is completed, the gate voltage becomes about −15 V and the gate current almost stops flowing therein. Further, in some cases, the gate current flowing during a period from the start to end of the discharge of the gate input capacitance
6
is simply referred to as “discharging current”.
FIG. 15
is a view showing a relation of the gate voltage V
ge
, the gate current I
ge
and a collector current I
C
at the time when the IGBT
7
of
FIG. 14
is turned on, and the gate current I
ge
corresponds to the charging current of the IGBT
7
. As shown in
FIG. 15
, when the transistor
4
a
is turned on, the gate current I
ge
for charging the gate input capacitance
6
largely flows, in other words, the charging current largely flows, and after that, as the gate input capacitance
6
is being charged, in other words, as the gate voltage V
ge
increases, the gate current I
ge
decreases and when the gate voltage V
ge
becomes almost equivalent to the voltage outputted from the control power supply
15
a
, the gate current I
ge
almost stops flowing.
As discussed above, with the charging current supplied by the control power supply
15
a
, the IGBT
7
is turned on. In other words, the control power supply
15
a
needs power capacity to supply the charging current. Similarly, in order to turn the IGBT
7
off, the control power supply
15
b
needs power capacity to supply the discharging current. Then, in order to increase a rated current between the emitter and collector of the IGBT
7
, it is usually necessary to increase the chip size of the IGBT
7
, which leads to an increase of the gate input capacitance
6
. For this reason, driving the IGBT
7
having a large rated current needs the control power supplies
15
a
and
15
b
having large power capacity. Further, when the IGBT
7
is used for an inverter device, as the operating frequency of the inverter device, i.e., the switching frequency of the IGBT
7
becomes higher, the charging current flowing per unit time becomes larger. For this reason, faster driving the IGBT
7
needs the control power supplies
15
a
and
15
b
having large power capacity. Thus, as the rated current of the IGBT
7
increases, and as faster driving of the IGBT
7
is desired, the power capacity of the control power supplies
15
a
and
15
b
required to drive the IGBT
7
increases.
The increase in power capacity of the control power supplies
15
a
and
15
b
as discussed above leads to an increase in cost and packaging volume of the control power supplies
15
a
and
15
b
. For this reason, in recent years when it is desired to reduce the cost and size of semiconductor devices, reduction of required power capacity of the control power supplies
15
a
and
15
b
is needed.
Then, a second background art is proposed, where the required power capacity of the control power supplies
15
a
and
15
b
are reduced.
FIG. 16
is a view showing a configuration of a semiconductor device in the second background art. The semiconductor device of the second background art further comprises capacitors
11
a
and
11
b
besides the configuration of the first background art discussed above.
As shown in
FIG. 16
, when both the transistors
4
a
and
4
b
are in an off state, the capacitors
11
a
and
11
b
are charged by the control power supplies
15
a
and
15
b
. Then, in order to turn on the IGBT
7
, when the gate driving circuit
3
turns the transistor
4
a
on and turns the transistor
4
b
off, electric charges accumulated in the capacitor
11
a
go through the transistor
4
a
to be supplied to the gate input capacitance
6
of the IGBT
7
where the supplied electric charges are accumulated. By the way, the gate current I
ge
of the IGBT
7
largely flows first when the transistor
4
a
is turned on and after that gradually decreases, as shown in FIG.
15
. In short, the control power supply
15
a
of the first background art needs current supplying capability to produce the peak value of the gate current I
ge
as shown in FIG.
15
. In the above-discussed second background art, since the electric charges accumulated in the capacitor
11
a
are supplied to the gate input capacitance
6
when the transistor
4
a
is turned on, the current supplied directly to the gate input capacitance
6
by the control power supply
15
a
decreases. For this reason, the control power supply
15
a
of the second background art does not need the current supplying capability to produce the peak value of the gate current I
ge
as shown in FIG.
15
. In other words, it is possible to reduce the required power capacity of the control power supply
15
a.
Further, in order to turn off the IGBT
7
, when the gate driving circuit
3
turns the transistor
4
a
off and turns the transistor
4
b
on, the electric charges accumulated in the gate input capacitance
6
go through the transistor
4
b
to be supplied to the capacitor
11
b
. For this reason, like for the control power supply
15
a
,
Furuie Toshiyuki
Honda Nobuhisa
Flynn Nathan J.
Forde Remmon R.
Mitsubishi Denki & Kabushiki Kaisha
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