Light emission control circuit uniformly and non-uniformly controlling a plurality of light-emitting elements

• US 7,391,406 B2
• Filed: 07/15/2004
• Issued: 06/24/2008
• Est. Priority Date: 09/12/2003
• Status: Expired due to Fees

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Yamamoto, Isao, Miyanaga, Koichi
• Primary Examiner(s): Awad; Amr A.
• Assistant Examiner(s): Moon; Seokyun
• Application Number:
  US10/892,029
• Publication Number:
  US 20050057554A1
• Time in Patent Office: 1,440 Days
• Field of Search: 345/211, 345/691, 345/102, 345/690, 345/52, 345/87, 345/88, 345/76, 345/77
• US Class Current: 345/102
• CPC Class Codes: H05B 45/20 Controlling the colour of the light
• CPC Class Codes: H05B 45/38 using boost topology
• CPC Class Codes: H05B 45/46 having LEDs disposed in parallel lines
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A booster converter outputs a boosted voltage. A plurality of LEDs emit light of respective colors. The transistors establish or shut connection between the LEDs and a main driving circuit. A variable current circuit feeds a current to drive the LEDs. A PWM control unit effects control to cause the LEDs to emit light with respective tones of color. A PWM circuit executes PWM modulation in accordance with an instruction from the PWM control unit. A setting control unit 138 controls the magnitude of the driving current fed by the variable current circuit in accordance with an instruction from a second light emission control unit. In an image pickup mode, an additional driving circuit feeds a driving current to the LEDs so that the LEDs operate as an electronic flash.

Claims

1. A light emission control circuit comprising:

a booster circuit for boosting a voltage of a constant-voltage source so as to drive a plurality of light-emitting elements corresponding to respective colors;

variable current circuits for driving the plurality of light-emitting elements;

switch elements for establishing or shutting connection between the light-emitting elements and the variable current circuits;

a first control unit for controlling the capability of said variable current circuits to drive the plurality of light-emitting elements;

a second control unit for turning on and off said switch elements according to pulse width modulation; and

an additional driving circuit which

     1) feeds a driving current to the plurality of light-emitting elements when operating the plurality of light-emitting elements as an electronic flash light,

     2) connects a variable power source to the light-emitting elements via a switch for electronic flash light, a transistor and a differential amplifier,

     3) connects a resistor to the source terminal of the transistor and the non-inverting input terminal of the differential amplifier, and

     4) uses the variable power source to set a driving current for electronic flash light, wherein

said first control unit adjusts luminance, responsive to an external instruction from a controller, produced by the entirety of the plurality of light-emitting elements, by controlling driving currents of the variable current circuits so that the ratio of the currents driving the plurality of light-emitting elements remains unchanged; and

said second control unit adjusts tone of color, responsive to an external instruction from the controller, produced by the entirety of the plurality of light-emitting elements, by independently controlling the duty ratio of pulse signals from the switch elements.

2. The light-emission control circuit according to claim 1, wherein, in each of the plurality of light-emitting systems, the switch element is constructed of a transistor provided between the light-emitting element and the variable current circuit, and wherein the transistor establishes or shuts connection between the light-emitting element and the variable current circuit.

3. The light-emission control circuit according to claim 1, wherein said first control unit increase a current for driving the plurality of light-emitting elements to increase the luminance of the plurality of light-emitting elements.

4. The light-emission control circuit according to claim 1, wherein said second control unit stores, for on and off control, data designating on and off of said switch elements according to a predetermined rule.

5. The light-emission control circuit according to claim 1, wherein said second control unit stores, for on and off control, data designating said switch elements corresponding to the plurality of light-emitting systems to be turned on for durations different from element to element.

6. The light-emission control circuit according to claim 1, wherein said second control unit extends, for on and off control, a duration of on period of a desired one of said switch elements in order to increase the quantity of light emitted by the corresponding light-emitting system.

7. A light emission control circuit comprising:

a booster circuit for boosting a voltage of a constant-voltage source so as to drive a plurality of light-emitting elements corresponding to respective colors;

variable current circuits for driving the plurality of light-emitting elements;

switch elements for establishing or shutting connection between the light-emitting elements and the variable current circuits;

a first control unit for controlling the capability of said variable current circuits to drive the plurality of light-emitting elements;

a second control unit for turning on and off said switch elements according to pulse width modulation; and

an additional driving circuit which

     1) feeds a driving current to the plurality of light-emitting elements when operating the plurality of light-emitting elements as an electronic flash light,

     2) connects a variable power source to the light-emitting elements via a switch for electronic flash light, a transistor and a differential amplifier,

     3) connects a resistor to the source terminal of the transistor and the non-inverting input terminal of the differential amplifier, and

     4) uses the variable power source to set a driving current for electronic flash light, wherein

said first control unit adjusts tone of color, responsive to an external instruction from a controller, produced by the entirety of the plurality of light-emitting elements, by independently controlling currents of the variable current circuits for driving the plurality of light-emitting elements, and

said second control unit adjusts luminance, responsive to and external instruction from the controller, produced by the entirety of the plurality of light-emitting elements, by controlling the duty ratio of pulse signals from the switch elements so that the duty ratio of the pulse signals remains unchanged.

8. The light emitting circuit according to claim 7, wherein, in each of the plurality of light-emitting systems, the switch element is constructed of a transistor provided between the light-emitting element and the variable current circuit, and wherein the transistor establishes or shuts connection between the light-emitting element and the variable current circuit.

9. The light-emission control circuit according to claim 7, wherein said first control unit increase a current for driving the plurality of light-emitting elements to increase the luminance of the plurality of light-emitting elements.

10. The light-emission control circuit according to claim 7, wherein said second control unit stores, for on and off control, data designating on and off of said switch elements according to a predetermined rule.

11. The light-emission control circuit according to claim 7, wherein said second control unit stores, for on and off control, data designating said switch elements corresponding to the plurality of light-emitting systems to be turned on for durations different from element to element.

12. The light-emission control circuit according to claim 7, wherein said second control unit extends, for on and off control, a duration of on period of a desired one of said switch elements in order to increase the quantity of light emitted by the corresponding light-emitting system.