Electric power conversion systems – Current conversion – Including d.c.-a.c.-d.c. converter
Reexamination Certificate
2001-04-24
2002-07-02
Vu, Bao Q. (Department: 2838)
Electric power conversion systems
Current conversion
Including d.c.-a.c.-d.c. converter
C323S349000, C323S901000
Reexamination Certificate
active
06414855
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to the structure of a power converter comprising a power conversion element and the structure of a semiconductor device employed for this power converter.
2. Description of the Background Art
FIG. 13
is a circuit diagram showing the structure of a conventional power converter
101
. Referring to
FIG. 13
, the conventional power converter
101
is applied to a drive unit for an ignition coil
105
. The ignition coil
105
controls an ignition plug
104
employed for the engine of an automobile. The power converter
101
individually comprises a semiconductor device
102
and another semiconductor device
103
. In the semiconductor device
102
, a power conversion element such as an IGBT (insulated gate bipolar transistor)
119
and Zener diodes
120
and
121
are formed on the same chip employing a silicon substrate. The IGBT
119
may be replaced with another element such as a power MOSFET or a bipolar power transistor. What kind of element is employed as the power conversion element is not important for the present invention but any one of existing elements and currently studied elements may be employed. The following description is made with reference to the IGBT employed as the power conversion element.
The Zener diodes
120
and
121
are elements specific to the drive unit for driving the ignition coil. The IGBT
119
is formed as an aggregate of small elements referred to as cells, and emitter wires for these cells are divided into two systems for intentionally causing difference between the numbers of the cells connected to the respective emitter wires. The magnitude of a current flowing in an emitter depends on the ratio of cell numbers, and hence a collector current (main current flowing in the power conversion element) of the IGBT
119
can be indirectly measured by detecting a small current having unique correlation with the current flowing in the power conversion element.
In the semiconductor
103
, a difference voltage comparison circuit
109
, a power supply circuit
110
, a high voltage detection circuit
111
, protective elements
113
and
114
, a timer circuit
115
, a logic gate
116
, an output circuit formed by an npn transistor
117
and a negative feedback control circuit
118
are formed on the same chip employing a silicon substrate.
The difference voltage comparison circuit
109
has two input terminal, and the first input terminal is connected to a terminal
107
(control input terminal from a control unit (not shown)) of the power converter
101
through a circuit formed by a resistance and a capacitor. The second input terminal is connected to another terminal
108
(reference potential input terminal from the aforementioned control unit (not shown)) of the power converter
101
through the aforementioned circuit. The difference voltage comparison circuit
109
has a waveform shaping function exhibiting a hysteretic characteristic, in order to prevent a malfunction resulting from fluctuation of the potential of the silicon substrate employed for the semiconductor device
103
. The difference voltage comparison circuit
109
is formed by a Schmidt circuit exhibiting a hysteretic characteristic and other elements.
The timer circuit
115
is provided for preventing the IGBT
119
from breakage resulting from heat generated when the IGBT
119
is continuously energized over a long period. When the IGBT
119
is continuously energized in excess of a prescribed time (several 100 ms) and the voltage of a capacitor (proportionate to the energization time for the IGBT
119
) input in a positive phase input terminal of a comparator exceeds a prescribed constant voltage input in a negative phase input terminal, the timer circuit
115
regards that the quantity of heat generated from the IGBT
119
is increased and inputs a signal for stopping drive of the npn transistor
117
in the logic gate
116
.
The power supply circuit
110
supplies power for driving various circuits provided in the semiconductor device
103
. The battery voltage (the voltage of a battery
106
) of the automobile fluctuates in a wide range (about several V to 24 V), and hence the power supply circuit
110
generating a constant power supply voltage regardless of the voltage of the battery
106
is provided in order to stably operate the timer circuit
115
, a waveform shaping circuit provided in the difference voltage comparison circuit
109
and the like.
The high voltage detection circuit
111
has a function of forcibly stopping drive of the IGBT
119
when the voltage of the battery
106
is abnormally increased, in order to prevent breakage. The high voltage detection circuit
111
detects that the voltage of the battery
106
exceeds a prescribed voltage (about 30 V) and inputs a signal for stopping drive of the npn transistor
117
in the logic gate
116
.
The negative feedback control circuit
118
has a function of detecting the value of the emitter current of the IGBT
119
and controlling operations of the IGBT
119
so that the main current does not flow in excess of a prescribed value. When the voltage input in the negative phase input terminal (voltage of a resistor connected to the emitter of the IGBT
119
, proportionate to the emitter current) exceeds the prescribed constant voltage input in the positive phase input terminal, the negative feedback control circuit
118
inputs a signal for stopping drive of the IGBT
119
in a gate electrode of the IGBT
119
.
The protective elements
113
and
114
have a function of suppressing a voltage applied to the circuit not to exceed a prescribed level, thereby protecting the circuit.
When the semiconductor device
103
drives the IGBT
119
by its control operation, a current flows toward a primary winding of the ignition coil
105
(toward the power converter
101
), and a resulting primary winding voltage is multiplied by the turn ratio and transmitted toward a secondary winding of the ignition coil
105
(toward the ignition plug
104
). Sparks come off between gaps of the ignition plug
104
due to this voltage to combust fuel in a cylinder (not shown) and provide motive power for the engine.
When stopping drive of the IGBT
119
and cutting off the current flowing toward the primary winding of the ignition coil
105
, energy stored in the ignition coil
105
generates force (counter electromotive force) stepping up a collector voltage of the IGBT
119
to the positive direction. When a voltage exceeding a reverse withstand voltage of the Zener diode
120
is caused, the Zener diode
120
operates to increase a gate voltage of the IGBT
119
and drive the OFF-state IGBT
119
as a result. Thus, the collector voltage is kept in a constant state.
In the conventional power converter
101
shown in
FIG. 13
, however, a number of circuits such as the difference voltage comparison circuit
109
, the timer circuit
115
, the negative feedback control circuit
118
and the like are formed in the semiconductor device
103
to disadvantageously increase the circuit scale of the semiconductor device
103
in particular.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention, a power converter comprises: a first semiconductor device including a first semiconductor substrate and a power conversion element formed on the first semiconductor substrate; and a second semiconductor device formed on a second semiconductor substrate different from the first semiconductor substrate for generating a control signal for controlling drive of the power conversion element and inputting the control signal in the first semiconductor device on the basis of a signal input from an external control unit.
According to a second aspect of the present invention, in the first aspect, the first semiconductor device further includes a cutoff circuit formed on the first semiconductor substrate for detecting the temperature of the first semiconductor substrate on a portion formed with the power conversion element and stopping drive of the power conversion
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