LED dimming apparatus

• US 8,339,053 B2
• Filed: 10/15/2008
• Issued: 12/25/2012
• Est. Priority Date: 10/25/2007
• Status: Active Grant

• Current Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Original Assignee: Panasonic Corporation (Panasonic Holdings Corporation)
• Inventors: Yamasaki, Shigeaki, Sako, Hiroyuki
• Primary Examiner(s): TRAN, THUY V
• Application Number:
  US12/738,148
• Publication Number:
  US 20100219764A1
• Time in Patent Office: 1,532 Days
• Field of Search: 315/209.R, 315/224, 315/246, 315/291, 315/307, 315/308
• US Class Current: 315/209.R
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/14 using electrical feedback from LEDs or from LED modules
• CPC Class Codes: H05B 45/34 Voltage stabilisation; Maintaining constant voltage
• CPC Class Codes: H05B 45/345 Current stabilisation; Maintaining constant current
• CPC Class Codes: H05B 45/385 using flyback topology
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

An LED dimming includes: current adjusting means (constant current circuit) for variably controlling a magnitude of a current flowing through an LED load; switching means (transistor) for intermittently controlling the current flowing through the LED load; and dimming controlling means (microcomputer) for controlling the current adjusting means and the switching means upon receiving a dimming signal outputted from a dimmer. In a case where the dimming signal outputted from the dimmer is on a higher brightness side than a predetermined level, the dimming controlling means flows a continuous current though the LED load, and dims the LED load based on a magnitude of the flowing current, and in a case where the dimming signal outputted from the dimmer is on a lower brightness side than the predetermined level, the dimming controlling means flows a pulse current through the LED load, and changes a mean value of waveforms of the pulse current, thereby dims the LED load. In this LED dimming apparatus, noise is less likely to occur even in a case where such an LED current is large, and brightness is less likely to vary even in a case where a dimming degree is increased.

Claims

1. An LED dimming apparatus, comprising:

a current adjuster for variably controlling a magnitude of a current flowing through an LED load;

a switch for intermittently controlling the current flowing through the LED load; and

a dimming controller for controlling the current adjuster and the switch upon receiving a dimming signal outputted from a dimmer,

wherein, in a case where the dimming signal outputted from the dimmer is on a higher brightness side than a predetermined level, the dimming controller flows a continuous current though the LED load, and dims the LED load based on a magnitude of the flowing current, and

in a case where the dimming signal outputted from the dimmer is on a lower brightness side than the predetermined level, the dimming controlling means flows a pulse current through the LED load, and changes a mean value of waveforms of the pulse current, thereby dims the LED load.

2. The LED dimming apparatus according to claim 1,

wherein the dimming controller includes:

a constant current controller for giving feedback of the current flowing through the LED load; and

a constant voltage controller for giving feedback of a load voltage applied to the LED load,

wherein in the case where the dimming signal outputted from the dimmer is on the higher brightness side than the predetermined level, the dimming controller flows a direct-current continuous current through the LED load by the constant current controller, and performs dimming control for the LED load based on a magnitude of the flowing current, and

in the case where the dimming signal outputted from the dimmer is on the lower brightness side than the predetermined level, the dimming controller sets the load voltage applied to the LED load by the constant voltage controller at a predetermined voltage, and at a same time, flows a pulse current through the LED load, and changes a mean value of waveforms of the pulse current, thereby dims the LED load.

3. The LED dimming apparatus according to claim 2,

wherein a range where the constant current controller for giving the feedback of the current flowing through the LED load and the voltage controller for giving the feedback of the load voltage applied to the LED load are used simultaneously is provided in the predetermined level.

4. The LED dimming apparatus according to claim 1,

wherein the predetermined level is set in a range where a ratio of a voltage change with respect to a current change becomes three to five times a case where a rated current is flown through the LED load in V-I characteristics of the LED load.

5. The LED dimming apparatus according to claim 1,

wherein the pulse current has a square waveform, and the dimming controller dims the LED load by changing a duty ratio of the square wave.

6. The LED dimming apparatus according to claim 1,

wherein, in a case where the dimming signal outputted from the dimmer is on a lower brightness side and the dimming signal is less than a second level, the second level being less than the predetermined level, the dimming controller switches a repetition frequency of the waveform of the pulse current to a lower frequency than the repetition frequency when the dimming signal is above the second level.

7. The LED dimming apparatus according to claim 1,

wherein the repetition frequency of the waveform of the pulse current is within a range of 60 Hz to 100 kHz.