POWER SUPPLY, LIGHT EMISSION CONTROL DEVICE AND DISPLAY DEVICE

• US 20090160367A1
• Filed: 02/06/2007
• Published: 06/25/2009
• Est. Priority Date: 02/17/2006
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Imanaka, Yoshinori
• Granted Patent: US 8,004,213 B2
• Time in Patent Office: Days
• US Class Current: 315/307
• CPC Class Codes: H02M 3/07 using capacitors charged and discharged alternately by semiconductor devices with control electrode , e.g. charge pumps
• CPC Class Codes: H02M 3/073 Charge pumps of the Schenkel-type
• CPC Class Codes: H02M 3/075 including a plurality of stages and two sets of clock signals, one set for the odd and one set for the even numbered stages
• CPC Class Codes: H05B 45/37 Converter circuits

Abstract

The power supply of the present invention is composed of: a charge pump circuit (54) that periodically turns on and off a plurality of charge-transfer switches (Q1 to Q4) according to clock signals (c1 and c2), thereby charges and discharges a charge storage capacitor (C1) and thus produces the desired output voltage (Vo) from an input voltage (Vi) to supply it to a load (LED); an output current detection circuit 57 for detecting an output current Io (a reference current (Im) thereof in FIG. 1) to the load; and means (a frequency conversion circuit 52 in FIG. 1) that varies the frequency of the clock signals c1 and c2 based on the result of the detection of the output current Io. With this configuration, it is possible to achieve high electric power efficiency irrespective of the magnitude of a load.

Claims

1. A power supply comprising:

a charge pump circuit arranged to periodically turns on and off a plurality of charge-transfer switches according to a clock signal, to thereby charges and discharges a charge storage capacitor and thereby produces a desired output voltage from an input voltage to supply the thus produced output voltage to a load,

wherein a frequency of the clock signal is varied according to a current flowing through the load.

2. The power supply of claim 1 arranged so that as the current flowing through the load increases, the frequency of the clock signal increases, and as the current flowing through the load decreases, the frequency of the clock signal decreases.

3. The power supply of claim 1, arranged so that as the current flowing through the load is detected by an output current detection circuit detecting a current commensurate with the output current.

4. The power supply of claim 3, wherein the output current detection circuit comprises:

a transistor to extract the current commensurate with the output current;

a sense resistor through which the current commensurate with the output current flows; and

a comparator whose output level varies according to a potential difference across the sense resistor.

5. The power supply of claim 4, wherein the output current detection circuit is arranged to detects whether the output current is higher than a predetermined threshold, the frequency of the clock signal being set at a first frequency if the output current is higher than the predetermined threshold, the frequency of the clock signal being set at a second frequency lower than the first frequency if the output current is lower than the predetermined threshold.

6. The power supply of claim 1 arranged such that the current flowing through the load is monitored through monitoring of a predetermined control signal used to control a drive current for the load.

7. The power supply of claim 6, further comprising:

a drive current generating circuit to generate the drive current for the load; and

a digital-to-analog converter to generate an analog control signal suitable for control of the drive current generating circuit from a digital control signal for setting the drive current supplied to the load,

wherein the control signal used for monitoring the current flowing through the load is the digital control signal.

8. The power supply of claim 7, arranged such that if the drive current required based on the control signal is higher than a predetermined threshold, the frequency of the clock signal is set at a first frequency, and if the required drive current is lower than the predetermined threshold, the frequency of the clock signal is set at a second frequency lower than the first frequency.

9. The power supply of any one of claims 1 to 8, further comprising:

an oscillation circuit to generate a clock signal having a predetermined frequency; and

a frequency conversion circuit to vary the frequency of the clock signal,

wherein the frequency of the clock signal of the charge pump circuit is varied by the frequency conversion circuit.

10. The power supply of any one of claims 1 to 8, further comprising an oscillation circuit to generate a clock signal having a predetermined frequency,

wherein the frequency of the clock signal of the charge pump circuit is varied by the oscillation circuit.

11. A light emission control device comprising:

a power supply to supply electric power to a light source serving as a load; and

a controller to vary a drive current for the light source based on a predetermined control signal,

wherein the means for supplying electric power to the load is the power supply of any one of claims 1 to 8.

12. A display device comprising:

a display panel;

a light source to illuminate the display panel; and

a controller to control light emission of the light source,

wherein the means for controlling light emission of the light source is the light emission control device of claim 11.