LIGHT EMITTER DRIVING DEVICE AND LIGHTING APPLIANCE THEREWITH

• US 20120326616A1
• Filed: 06/20/2012
• Published: 12/27/2012
• Est. Priority Date: 06/23/2011
• Status: Active Grant

• Current Assignee: ROHM Co., Ltd.
• Original Assignee: ROHM Co., Ltd.
• Inventors: Sumitani, Takeshi, Sawada, Akinobu
• Granted Patent: US 8,922,135 B2
• Time in Patent Office: Days
• US Class Current: 315/201
• CPC Class Codes: H05B 44/00 Circuit arrangements for operating electroluminescent light sources for operating light emitting diodes H05B45/00
• CPC Class Codes: H05B 45/10 Controlling the intensity of the light
• CPC Class Codes: H05B 45/44 with an active control inside an LED matrix
• CPC Class Codes: Y02B 20/30 Semiconductor lamps, e.g. solid state lamps [SSL] light emitting diodes [LED] or organic LED [OLED]

Abstract

A light emitter driving device has a decoder portion which monitors a rectified voltage and generates a dimming signal, and a drive current control portion which controls a drive current to a light emitter according to the dimming signal. The decoder portion has a comparator which compares the rectified voltage with a predetermined threshold voltage to generate a comparison signal, a sampling counter which measures high-level and low-level periods of the comparison signal, a duty calculation portion which calculates the duty of the rectified voltage based on the output of the sampling counter, a filter calculation portion which excludes sporadic variation in duty by applying digital filtering to the output of the duty calculation portion, and a dimming signal generation portion which generates the dimming signal based on the output of the filter calculation portion.

Claims

1. A light emitter driving device comprising:

a decoder portion that monitors a rectified voltage and generates a dimming signal; and

a drive current control portion that controls a drive current for the light emitter in accordance with the dimming signal;

wherein

the decoder portion includes;

a comparator that compares the rectified voltage with a predetermined threshold voltage to generate a comparison signal;

a sampling counter that measures a high level time span and a low level time span of the comparison signal;

a duty calculation portion that calculates a duty of the rectified voltage in accordance with an output from the sampling counter;

a filter operation portion that applies a digital filter process to an output from the duty calculation portion to remove a sudden duty change; and

a dimming signal generation portion that generates the dimming signal based on an output from the filter operation portion.

2. The light emitter driving device according to claim 1, wherein

the filter operation portion includes a median filter.

3. The light emitter driving device according to claim 2, wherein

the median filter includes:

a FIFO portion that that stores a group of duties which are successively calculated over a plurality of periods; and

a selection portion that selects a middle value from or a value larger than the middle value from the group of duties stored in the FIFO portion and outputs the value.

4. The light emitter driving device according to claim 2, wherein

the filter operation portion further includes a hysteresis filter.

5. The light emitter driving device according to claim 2, wherein

the filter operation portion further includes a FIR filter.

6. The light emitter driving device according to claim 1, wherein

the decoder portion further includes:

a frequency calculation portion that calculates a frequency of the rectified voltage in accordance with the output from the sampling counter;

a frequency determination portion that determines whether the frequency of the rectified voltage falls in a predetermined range or not; and

a mask process portion that applies a mask process to the output from the duty calculation portion in accordance with a determination result from the frequency determination portion.

7. The light emitter driving device according to claim 1, wherein

the decoder portion further includes:

a mask signal generation portion that generates a mask signal which changes in logic level at every rise of the rectified voltage; and

a mask process portion that applies a mask process to the output from the duty calculation portion in accordance with the mask signal.

8. A lighting appliance comprising:

a light emitter;

a rectification circuit that rectifies an a.c. voltage to generate a rectified voltage;

a smoothing circuit that generates a d.c. voltage from the rectified voltage and supplies the de voltage to the light emitter;

a switch device that opens/closes an electric current route in which a driving current for the light emitter flows; and

a light emitter driving device that performs on/off control of the switch device;

wherein

the light emitter driving device includes;

a decoder portion that monitors the rectified voltage and generates a dimming signal; and

a drive current control portion that controls a drive current for the light emitter in accordance with the dimming signal;

wherein

the decoder portion includes;

a comparator that compares the rectified voltage with a predetermined threshold voltage to generate a comparison signal;

a sampling counter that measures a high level time span and a low level time span of the comparison signal;

a duty calculation portion that calculates a duty of the rectified voltage in accordance with an output from the sampling counter;

a filter operation portion that applies a digital filter process to an output from the duty calculation portion to remove a sudden duty change; and

a dimming signal generation portion that generates the dimming signal based on an output from the filter operation portion.

9. The lighting appliance according to claim 8, wherein the drive current control portion performs the on/off control of the switch device such that a current flowing in the switch device becomes equal to a target value which is set based on the dimming signal.

10. The lighting appliance according to claim 8, further comprising

a bleeder circuit that keeps a hold current of a TRIAC dimmer which performs phase control of the a.c. voltage.

11. The lighting appliance according to claim 8, wherein

the light emitter includes an LED device.

12. The lighting appliance according to claim 11, wherein

the lighting appliance is a bulb-shaped lamp, an annular-shaped LED lamp, a linear tube-shaped LED lamp, a ceiling light, or a downlight.