Electricity: power supply or regulation systems – In shunt with source or load – Using a three or more terminal semiconductive device
Reexamination Certificate
2001-08-13
2002-09-17
Sterrett, Jeffrey (Department: 2838)
Electricity: power supply or regulation systems
In shunt with source or load
Using a three or more terminal semiconductive device
C323S271000, C323S351000
Reexamination Certificate
active
06452365
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a power converter to be suitably utilized for an inverter and a signal level converter to be suitably utilized for the power converter and more particularly to an improvement for increasing a breakdown voltage of the device without requiring a complicated manufacturing process while maintaining a stable operation.
2. Description of the Background Art
In a signal level converting circuit to function as an interface between a power switching element and an MPU (microcomputer) for driving and controlling the power switching element, conventionally, a photocoupler has been used for electrical insulation. In recent years, however, an HVIC (High Voltage Integrated Circuit) has been used because of advantages such as a small size, a low cost and a long lifetime.
FIG. 16
is a block diagram showing a conventional inverter using the HVIC. An inverter
150
comprises three power converters
151
to
153
having the same structure. The three power converters
151
to
153
share each of three-phase outputs U, V and W. Each of the power converters
151
to
153
is provided between a high potential power line PP and a low potential power line (grounding conductor) NN and receives the supply of a d.c. source voltage from an external power source
165
. Moreover, a control signal is input from an external microcomputer
160
to each of the power converters
151
to
153
.
The power converter
151
includes power switching elements
172
and
173
, free wheel diodes
174
and
175
, a capacitor
170
and an HVIC (High Voltage Integrated Circuit)
154
. In an example of
FIG. 16
, the power switching elements
172
and
173
are IGBTs (Insulated Gate Bipolar Transistors). A load is connected through a wiring OUT (U) to a connecting portion of the power switching elements
172
and
173
connected to each other in series.
The HVIC
154
includes a buffer
166
, driving circuits
169
and
171
, a switching element
167
and a resistive element
168
. In the example of
FIG. 16
, the switching element
167
is an N-channel type high voltage MOSFET. A source voltage is supplied from an external d.c. power source
161
to the buffer
166
and the driving circuit
171
. A voltage held by the capacitor
170
is supplied as a source voltage to a driving circuit
169
changing a source potential together with the wiring OUT (U). When the power switching element
173
is turned ON or OFF, the d.c. power source
161
repetitively charges the capacitor
170
through a resistive element
163
and a diode
164
.
A level of a signal to be transmitted is varied between the buffer
166
and the driving circuit
169
. A series circuit of the switching element
167
and the resistive element
168
which is provided between the buffer
166
and the driving circuit
169
functions as a level shift circuit for converting a level of a signal between the buffer
166
and the driving circuit
169
. Accordingly, a breakdown voltage which is equal to or higher than that of the power switching element
172
is required for the switching element
167
.
The HVIC has problems, for example, if a breakdown voltage becomes higher, a manufacturing process is more complicated, a manufacturing apparatus is to be introduced newly, a malfunction of the HVIC itself cannot be prevented easily, and the like. In the HVIC, a technique for isolating a low voltage portion from a high voltage portion is a key technology. A junction isolation technique and a dielectric isolation technique have been known as the isolation technique. In the junction isolation technique, an isolation island is formed of an isolating p
+
layer by using a method standardly utilized in a normal IC or LSI, and an element or a circuit as an element group is formed on the inside thereof. In the dielectric isolation technique, each of single crystal silicon islands forming each element or circuit is surrounded by a dielectric (for example, a polycrystalline silicon). Consequently, the islands are electrically insulated from each other.
The junction isolation technique has such an advantage as to be carried out by a conventional IC manufacturing apparatus. In some cases, however, a noise current flows to a floating capacitance in an isolation region through dv/dt (a rate of change in a voltage) during a switching operation so that an operation of the circuit is affected. There is a problem in that the phenomenon presents itself more remarkably when a breakdown voltage is increased. The dielectric isolation technique includes a special process such as the bonding of a silicon substrate. Therefore, there is a problem in that a manufacturing process is complicated and a cost per unit chip area is increased. In addition, as a breakdown voltage is more increased, the manufacturing process becomes more complicated so that the cost is more increased.
Up to the present, an HVIC having a breakdown voltage of 600 V has been put on the market. However, if the breakdown voltage is to be more increased, the above-mentioned problems actually arise. Therefore, an increase in the breakdown voltage of the HVIC has not been implemented.
SUMMARY OF THE INVENTION
In order to solve the above-mentioned problems in the conventional art, it is an object of the present invention to provide a power converter and a signal level converter which can increase a breakdown voltage without requiring a complicated manufacturing process while maintaining a stable operation.
A first aspect of the present invention is directed to a power converter comprising a first switching element having first and second main electrodes, a second switching element having third and fourth main electrodes, the fourth main electrode being connected to the first main electrode, a first driving circuit to drive the first switching element based on a first control signal input from an outside, a second, driving circuit to drive the second switching element based on a second control signal input from an outside, and n level shift circuits connected in cascade in n stages, the n being an integer of 2 or more, and configured to level shift the first control signal in the n stages and to transmit the level shifted signal to the first driving circuit.
A second aspect of the present invention is directed to the power converter according to the first aspect of the present invention, further comprising a sense circuit to detect an operation state of the first switching element and to output a detection signal representing the operation state, and n other level shift circuits connected in cascade in n stages and configured to level shift the detection signal in the n stages and to transmit the level shifted signal to an outside.
A third aspect of the present invention is directed to the power converter according to the second aspect of the present invention, further comprising a one-shot pulse circuit connected to an input of each of the n other level shift circuits, and a latch circuit connected to an output of each of the n other level shift circuits.
A fourth aspect of the present invention is directed to the power converter according to any of the first to third aspects of the present invention, further comprising a one-shot pulse circuit connected to an input of each of the n level shift circuits, and a latch circuit connected to an output of each of the n level shift circuits.
A fifth aspect of the present invention is directed to the power converter according to any of the first to fourth aspects of the present invention, wherein each of the n level shift circuits includes a resistive element and a switching element which are connected to each other in series.
A sixth aspect of the present invention is directed to the power converter according to the second aspect of the present invention, wherein each of the n other level shift circuits includes a resistive element and a switching element which are connected to each other in series.
A seventh aspect of the present invention is directed to the power converter according to any of th
Hatae Shinji
Majumdar Gourab
Yoshimura Kousuke
Mitsubishi Denki & Kabushiki Kaisha
Sterrett Jeffrey
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