Electric power conversion systems – Current conversion – Using semiconductor-type converter
Reexamination Certificate
1999-05-19
2001-02-20
Wong, Peter S. (Department: 2838)
Electric power conversion systems
Current conversion
Using semiconductor-type converter
C327S540000, C323S311000
Reexamination Certificate
active
06191967
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATION
This application is based upon and claims benefit of priority of Japanese Patent Application No. Hei-10-138323 filed on May 20, 1998, the content of which is incorporated herein by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a voltage supply device which drives a relatively high voltage load such as an electroluminescent display panel, and more particularly to such a device that includes a circuit for testing its own operation under a test voltage that is considerably lower than a normal operation voltage.
2. Description of Related Art
An example of a voltage supply device for driving scanning and data electrodes of an electroluminescent display panel is disclosed in JP-A-8-137433. In this device, an output circuit for selectively outputting a high voltage and a ground voltage, essence of which is shown in
FIG. 4
, is used. An output circuit
3
composed of a P-channel MOSFET
1
and an N-channel MOSFET
2
, both connected in series, is connected between a plus terminal +V and a ground terminal GND of a high voltage source. Both MOSFETs
1
and
2
constitute a push-pull circuit, and an output terminal
4
is connected to a junction of both MOSFETs. A gate voltage switching circuit
5
composed of plural resistances
6
and an N-channel MOSFET
7
, all connected in series, is connected in parallel to the output circuit
3
. A divider terminal
6
a
of the switching circuit
5
is connected to a gate of the MOSFET
1
. An input terminal
8
is connected to a gate of the MOSFET
7
, and another input terminal
9
is connected to a gate of the MOSFET
2
.
The MOSFET
7
is turned on when a signal is fed from the input terminal
8
, thereby bringing a voltage at the divider terminal
6
a
to a level that turns on the MOSFET
1
and is a little lower than the plus terminal voltage +V. When the MOSFET
1
is turned on, the voltage at the output terminal
4
becomes the plus terminal voltage +V. The MOSFET
2
is turned on when a signal is fed from the input terminal
9
, thereby bringing the output voltage at the output terminal
4
to the ground level GND. The input signals fed from the input terminals
8
and
9
are relatively low, e.g., 5 V that is the same as an operating voltage of a control circuit. Thus, the output voltage of the output terminal
4
is selectively switched between +V and GND, and is supplied to electrodes of an electroluminescent display panel.
Usually, operation of the driver IC including the output circuit
3
, i.e., whether the output from the output terminal
4
is selectively switched between +V and GND according to the input signals fed from the input terminals
8
and
9
, is tested after completion of the driver IC. To test the operation of the conventional driver IC, it is necessary to supply a power source voltage that is as high as 150 V, for example. Therefore, the test is not easy, and a testing apparatus having a high voltage is required.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above-mentioned problem, and an object of the present invention is to provide an improved power supply device in which an operation test can be performed under a low voltage even if the power supply device itself outputs a high voltage. Another object of the present invention is to provide a method of testing such a device under a low voltage.
An output circuit, connected to a high voltage terminal and a ground terminal of a power source having a relatively high voltage, e.g., 150 V, selectively outputs the high voltage and the ground voltage under a normal operation. The output circuit includes a first switching transistor and a second switching transistor, both connected in series, and outputs the high voltage when the first transistor is turned on and the ground voltage when the second transistor is turned on. Both switching transistors are turned on or off by controlling the gate voltage thereof.
Operation of the voltage supply device is switched between a normal operation mode in which the device is operated under a high voltage, e.g., 150 V and a test mode in which the device is tested under a low voltage, e.g., 5 V, the same voltage as a control circuit voltage. The operation and test modes are switched based on an external signal fed to the device. Under the operation mode, the first switching transistor is turned on with a high gate voltage that is a little lower than the terminal voltage (only clearing a threshold voltage of the first switching transistor), and the second switching transistor is turned on with a low gate voltage, e.g., 5 V. Under the test mode, the first switching transistor is turned on with a low gate voltage, e.g., the ground voltage, and the second switching transistor is turned on with the same low gate voltage as under the operation mode. Those gate voltages are switched by a gate voltage switching circuit built in the voltage supply device according to the external signals indicating either the operation mode or the test mode.
An additional external signal for prohibiting both of the first and second switching transistors from being tuned on may be provided in the device to suppress unnecessary power consumption. A plurality of the output circuits each including its own controlling circuit may be integrated into a single chip that constitutes a voltage supply device as a whole.
According to the present invention, the voltage supply device normally operated under a high voltage can be tested under a low voltage, using its own built-in circuits. Therefore, the device is easily tested without supplying a high voltage thereto.
Other objects and features of the present invention will become more readily apparent from a better understanding of the preferred embodiment described below with reference to the following drawings.
REFERENCES:
patent: 4782290 (1988-11-01), Sakai et al.
patent: 5023476 (1991-06-01), Watanabe et al.
patent: 5870296 (1999-02-01), Schaffer
patent: 5-119339 (1993-05-01), None
patent: 8-137433 (1996-05-01), None
patent: 9-74345 (1997-03-01), None
Hirano Tetsuo
Iwamura Takahiro
Katayama Osamu
Denso Corporation
Patel Rajnikant B.
Pillsbury Madison & Sutro LLP
Wong Peter S.
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