LED DIMMER CIRCUIT

• US 20120249000A1
• Filed: 03/28/2012
• Published: 10/04/2012
• Est. Priority Date: 03/29/2011
• Status: Active Grant

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Inventors: Kawai, Shuhei, Goto, Tomoyuki, Xu, Feng
• Granted Patent: US 8,736,194 B2
• Time in Patent Office: Days
• US Class Current: 315/200.R
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/3725 Switched mode power supply [SMPS]

Abstract

A TRIAC dimmer gates an AC waveform from an AC power source in proportion to a control signal and outputs a TRIAC pulse having part of the waveform missing. The TRIAC pulse is rectified and is applied to an LED array and the drive current flowing to the LED array is detected at a current detection resistor. The drive current value and a predetermined value are compared at a comparator and in accordance with the comparison result thereof the control transistor is turned off. Then, the TRIAC pulse is converted to a DC voltage signal and in accordance with the obtained DC voltage signal the drive current value or the predetermined value input by the comparator are changed. Furthermore, instead of the TRIAC pulse, a PWM pulse supplied from an external source may also be utilized.

Claims

1. A light emitting diode (LED) dimmer circuit for performing LED dimming, comprising:

a triode for alternating current (TRIAC) dimmer for gating an alternating current (AC) waveform from an AC power source at a proportion according to a control signal and outputting a TRIAC pulse having part of the AC waveform missing;

a rectifying circuit for rectifying the TRIAC pulse from the TRIAC dimmer;

a current sensing circuit for detecting a drive current value flowing to an LED driven by an output of the rectifying circuit;

a control transistor for switching said drive current on and off;

a comparator circuit for comparing said drive current value detected by the current sensing circuit and a predetermined value;

a control circuit for turning off said control transistor when said drive current value exceeds said predetermined value in accordance with a comparison result of the comparator circuit and turning on said control transistor when a trigger pulse is applied;

a converter circuit for converting said TRIAC pulse to a DC voltage signal; and

a change circuit for changing said drive current value or said predetermined value to be input to said comparator circuit in accordance with said DC voltage signal.

2. An LED dimmer circuit according to claim 1, wherein:

said current sensing circuit detects a voltage drop voltage at a current detection resistor connected in series with said LED.

3. An LED dimmer circuit according to claim 1, wherein:

said converter circuit divides said TRIAC pulse according to resistance to obtain a divided voltage, integrates the obtained divided voltage, and obtains said DC voltage.

4. An LED dimmer circuit according to claim 1, wherein:

said change circuit changes said predetermined value.

5. An LED dimmer circuit according to claim 1, wherein:

said change circuit changes said drive voltage value.

6. An LED dimmer circuit according to claim 2, wherein:

said change circuit applies an output of said converter circuit via a diode to said voltage drop voltage of said current detection resistor to change said drive current value.

8. An LED dimmer circuit according to claim 6, wherein:

said current sensing circuit detects a voltage drop voltage at a current detection resistor connected in series with said LED.

9. An LED dimmer circuit according to claim 6, wherein:

said converter circuit divides said TRIAC pulse according to resistance to obtain a divided voltage, integrates the obtained divided voltage, and obtains said DC voltage.

10. An LED dimmer circuit according to claim 6, wherein:

said change circuit changes said predetermined value.

11. An LED dimmer circuit according to claim 6, wherein:

said change circuit changes said drive current value.

7. A light emitting diode (LED) dimmer circuit comprising:

a rectifying circuit for rectifying an alternating current (AC) waveform from an AC power source;

a current sensing circuit for detecting a drive current value flowing to an LED to be driven by an output of the rectifying circuit;

a control transistor for switching said drive current on and off;

a control circuit for comparing said drive current value detected by the current sensing circuit and a predetermined value, turning off said control transistor when said drive current value exceeds said predetermined value, and turning on said control transistor when a trigger pulse is applied;

a converter circuit for converting a pulse width modulation signal input from an external source and indicating a dimming degree to a DC voltage signal; and

a change circuit for changing said drive current value or said predetermined value to be input to said comparator circuit in accordance with said DC voltage signal.

12. An LED dimmer circuit according to claim 7, wherein:

said change circuit applies an output of said converter circuit via a diode to said voltage drop voltage of said current detection resistor to change said drive current value.