Power supply circuit, display device and electronic instrument

• US 20010020939A1
• Filed: 03/16/2001
• Published: 09/13/2001
• Est. Priority Date: 03/28/1997
• Status: Active Grant

• Current Assignee: Seiko Epson Corporation (Seiko Group)
• Original Assignee: Seiko Epson Corporation (Seiko Group)
• Inventors: Ikeda, Masuhide
• Granted Patent: US 6,377,252 B2
• Time in Patent Office: Days
• US Class Current: 345/211
• CPC Class Codes: G09G 2310/0205 Simultaneous scanning of several lines in flat panels
• CPC Class Codes: G09G 2310/0289 Details of voltage level shifters arranged for use in a driving circuit
• CPC Class Codes: G09G 2330/02 Details of power systems and of start or stop of display operation
• CPC Class Codes: G09G 2330/021 Power management, e.g. power saving
• CPC Class Codes: G09G 3/3644 with the matrix divided into sections
• CPC Class Codes: G09G 3/3696 Generation of voltages supplied to electrode drivers

Abstract

An object is to provide a power supply circuit, display device and electronic instrument which can reduce the power consumption in the power supply circuit itself and which can set a boosting ratio according to the duty ratio. The power supply circuit comprises: a charge pump circuit including a first switching unit (40) for charging a capacitor CP and a second switching unit (42) for transferring the charge in the capacitor CP to another capacitor CB; and a circuit for generating switching signals for controlling the first and second switching units. The first switching unit (40) includes switching elements SW11A and SW11B each of which is connected at one end to a different potential VDD or VE1, the other end thereof being connected to one end of the capacitor CP. The switching signal generation circuit controls ON and OFF-states of the switching element SW11A while turning the other switching element SW11B off, or controls ON and OFF-states of the switching element SW11B while turning the other switching element SW11A off. Thus, the boosting ratio can variably be controlled. The potential of the switching signal in the OFF state is equalized with a potential supplied to the source of a switching transistor. At a partial display on a liquid crystal display device, the boosting ratio is controlled according to the duty ratio.

Claims

1. A power supply circuit for converting a voltage and for supplying the converted voltage as a power supply voltage, said power supply circuit comprising:

at least one charge pump circuit which includes a first capacitor, a second capacitor, a first switching means for charging said first capacitor based on a given voltage, and a second switching means for transferring the charge in said first capacitor to said second capacitor; and

a switching signal generation circuit for generating a plurality of switching signals which control said first and second switching means;

wherein said first switching means includes a plurality of switching elements, one ends of said switching elements being electrically connected to different potentials, and the other ends thereof being electrically connected to at least one end of said first capacitor; and

wherein said switching signal generation circuit receives at least one given first control signal for controlling at least one of the boosting ratio and the deboosting ratio, and then generates said switching signals for controlling ON and OFF-states of one of said switching elements specified by said first control signal, and for turning off at least one other switching element.

2. The power supply circuit as defined in

claim 1

,

wherein said switching signal generation circuit comprises:

a circuit for generating a basic switching signal;

a decoder for decoding said first control signal; and

an output circuit for receiving the output of said decoder and said basic switching signal to output a switching signal generated based on said basic switching signal toward one of said switching elements to be ON-OFF controlled and to output a switching signal fixed at a given potential toward at least one other switching element not to be ON-OFF controlled.

3. The power supply circuit as defined in

claim 2

,

wherein said output circuit includes a level shifter for converting the amplitude of said basic switching signal on the basis of a reference potential as well as a charge pump potential from said charge pump circuit.

4. The power supply circuit as defined in

claim 1

,

wherein said switching signal generation circuit receives a reference potential and a charge pump potential of said charge pump circuit for setting the potentials of switching signals during the OFF-state period outputted toward switching transistors included in said first and second switching means at one of said reference potential and said charge pump potential both of which are supplied to the source of said switching transistors.

5. A display device comprising:

a power supply circuit as defined in any one of claims to 4;

a drive circuit for outputting scan and data signals based on the power supply voltage from said power supply circuit; and

a panel having scan lines into which said scan signals are inputted, data lines into which said data signals are inputted, and display elements driven by said scan and data lines;

wherein at least one of the boosting and deboosting ratios is varied by varying said first control signal according to the duty ratio in said panel.

6. The display device as defined in

claim 5

,

wherein a given second signal is used to select K scan lines among N scan lines and to unselect (N-K) scan lines for performing a partial display, and

wherein at the partial display, said first control signal is varied depending on the number of selected scan lines to vary at least one of the boosting and deboosting ratios.

7. An electronic instrument comprising:

a display device as de fined in

claim 5

; and

a central control means for processing for setting said first and second control signals.

8. An electronic instrument comprising:

a display device as defined in

claim 6

; and

a central control means for processing for setting said first and second control signals.

9. A power supply circuit for converting a voltage and for supplying the converted voltage as a power supply voltage, said power supply circuit comprising:

at least one charge pump circuit which includes a first capacitor, a second capacitor, a first switching means for charging said first capacitor based on a given voltage, and a second switching means for transferring the charge in said first capacitor to said second capacitor; and

a switching signal generation circuit for generating a plurality of switching signals which control said first and second switching means;

wherein said switching signal generation circuit receives a reference potential and a charge pump potential of said charge pump circuit for setting the potentials of switching signals during the OFF-state period outputted toward switching transistors included in said first and second switching means at one of said reference potential and said charge pump potential both of which are supplied to the source of said switching transistors.

10. The power supply circuit as defined in

claim 9

,

wherein said switching signal generation circuit sets the potentials of said switching signals during the OFF-state period based on a plurality of charge pump potentials from a plurality of charge pump circuits.

11. The power supply circuit as defined in

claim 9

,

wherein said switching, signal generation circuit comprises:

circuit for generating a basic switching signal; and

a level shifter for converting the amplitude of said basic switching signal based on said reference and charge pump potentials.

12. A display device comprising:

a power supply circuit as defined in any one of

claims 9

to

11

;

a drive circuit for outputting scan and data signals based on the power supply voltage from said power supply circuit; and

a panel having scan lines into which said scan signals are inputted, data lines into which said data signals are inputted, and display elements driven by said scan and data lines.

13. An electronic instrument comprising:

a display device as defined in

claim 12

; and

a central control means for processing for controlling said display device.