Voltage supply circuit

Details Voltage supply circuit Voltage supply circuit

2001-07-12

2002-10-22

Le, Dinh T. (Department: 2816)

Miscellaneous active electrical nonlinear devices, circuits, and

Specific identifiable device, circuit, or system

With specific source of supply or bias voltage

C327S530000, C327S537000

Reexamination Certificate

active

06469570

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a voltage supply circuit used as a power supply circuit of for example a liquid crystal display device (LCD panel).
BACKGROUND ART
For example, as a voltage for driving a LCD panel employing the thin film diode (referred to as MIM), three levels, that is, a signal electrode drive voltage V
D
, a high level selection voltage V
H
, and a low level selection voltage V
L
become necessary.
At this time, the signal electrode drive voltage VD, high level selection voltage V
H
, and the low level selection voltage V
L
must satisfy the following conditions when a virtual selection voltage is V
SEL
:
V
L
=−V
SEL
V
H
=V
D
+V
SEL
  (1)
Conventionally, in order to obtain these signal electrode drive voltage V
D
, high level selection voltage V
H
, and low level selection voltage V
L
, a so-called charge pump type voltage generation circuit has been used.
In a voltage supply circuit generating the above three voltages by a voltage generation circuit of the charge pump type, however, there were problems in that equation (1) could not be satisfied with a sufficient precision (particularly when turning on the power) and in that the number of parts of the circuit was too large due to the wide variable range of the virtual selection voltage V
SEL
(generally about 2 V to 20 V).
DISCLOSURE OF THE INVENTION
The present invention was made in consideration with such a circumstance and has as an object thereof to provide a voltage supply circuit capable of starting up a system while holding symmetry of the high level selection voltage and the low level selection voltage and capable of decreasing the number of parts of the system without the need of a multistage charge pump circuit.
To attain the above object, a voltage supply circuit of the present invention comprises a first voltage generation circuit including a chopper type switching regulator for comparing a first reference voltage and an output feedback voltage and generating a first output voltage, a second voltage generation circuit including a chopper type switching regulator for generating a second output voltage, a third voltage generation circuit including a charge pump for generating a third output voltage in accordance with the second output voltage, a virtual reference voltage generation circuit for generating a virtual reference voltage corresponding to the first output voltage, an intermediate voltage generation circuit for generating an intermediate voltage between the second output voltage and the third output voltage, a comparator for comparing!the virtual reference voltage and the intermediate voltage and outputting an error signal in accordance with the comparison result, and a control circuit for receiving as input the error signal and controlling operations of the second voltage generation circuit and the third voltage generation circuit so that the virtual reference voltage and the intermediate voltage become equal.
Also, in the present invention, the control circuit makes the third voltage generation circuit operate when a voltage difference between the virtual reference voltage and the second output voltage is larger than the voltage difference between the virtual reference voltage and the third output voltage and makes the second voltage generation circuit operate when the voltage difference between the virtual reference voltage and the second output voltage is smaller than the voltage difference between the virtual reference voltage and the third output voltage.
Also, in the present invention, the virtual reference voltage is a middle point potential between the first output voltage and a ground potential, and the intermediate potential is the middle point potential between the second output voltage and the third output voltage.
Further, in the present invention, the second output voltage is higher than the third output voltage.


REFERENCES:
patent: 5426334 (1995-06-01), Skovmand
patent: 6212107 (2001-04-01), Tsukada
patent: 6333864 (2001-12-01), Nishimura et al.
patent: U-63-147710 (1988-09-01), None

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