ac led drive technology

7/23/2019 AC LED Drive Technology

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A Novel Technique of Driving Light-Emitting-Diode (LED)

Teng Kong Leong

INTRODUCTION

Light-Emitting-Diode (LED) is a device that requires a constant DC

current across it in order to produce a light at certain wavelength.

It is straight-forward to power LED from DC system but not from AC

system. In AC system, a converter is required such as AC-DC switching

power supply to convert the incoming AC to constant DC current. With

AC-DC switching power supply will introduce complexity and used of

short lifetime electronic components. In order to solve these issues

Eurolicht has a novel technique with less complexity and eliminate the

short lifetime electronic components; hence, longer lifetime solid-

state-lighting products.

OPERATION

Conventional AC-DC switching power supply will convert the incoming AC,

110VAC or 230VAC 50/60Hz, to constant DC current in order to drive the

LED. With our novel technique different string of LED is switched on

and off based on the incoming AC line switching. Figure 1 illustrates

the block diagram of the driver.

Figure 1

The regulator integrated circuit will monitor the incoming AC line

regardless of frequency 50Hz or 60Hz and switch the LED on and off

Regulator

&

Control Circuit

HV LEDHV LED HV LEDHV LED HV LEDHV LED HV LEDHV LED

Current

Sense

Current

Sense

CurrentSenseCurrentSense



Channel 1

Channel 2

Channel 3

Channel 4



according to the LED total forward voltage per strings. When the

rectified AC line voltage reaches a certain level, an internal

reference and regulator starts to supply power to the internal

circuits. Upon power up, all current channels are ready to sink LEDcurrent and will drive the LED as long as the rectified AC line voltage

is higher or adequate headroom compared to the total string’s voltage.

As the rectified AC line voltage increases, each LED channel current

linearly increases up to the preset level and remain at that level till

the rectified AC line voltage level more than the total forward voltage

of the following LED strings. Figure 2 illustrates the current

transition as the rectified AC line voltage increases.

Figure 2

According to Figure 2, there are 4 groups or strings of LED connected

to 4 channels on the regulator IC. Group 1 will turn on when the

rectified AC line voltage level more than 88V, follows by Group 2 at176V, Group 3 at 220V, and Group 4 at 264V.

The current across the LED per string is adjustable via current sense

resistor which is feedback to the regulator IC. There are multiple

configurations of connecting the LED to the regulator IC depending on

requirement that one try to achieve.

Power Quality: Power Factor & THD

100V

50V

250V

200V

150V

88V

44V

132V

176V

220V

264V

300V

I4

I2 I2

40

mA

40

mA

I1I1

I3I3



Despite solid-state-lighting (SSL) high luminous efficacy and future

replacement of traditional lighting, power quality of SSL has been much

less compelling story. Power quality standards are being considered

for SSL products to obtain ENEGRY STAR certification. Due to this,most of LED driver IC maker started to integrate the digital signal

processing to improve the power quality that will greatly increases the

IC costs.

Power quality for any AC lamp indicates how the lamp draws current when

supplied with sinusoidal voltage from the incoming AC. Incandescent

lamps have a resistance that draws current as a linear load, but LED

has diodes that draw current as a non-linear load. As a consequence of

this non-linear behavior, some existing SSL exhibit poor power quality

in terms of both power factor (PF) and total harmonic distortion (THD).

With our techniques, the regulator IC will make sure that the alignment

of waveform peaks. The current waveform will be less distorted because

it conforms better to voltage waveform at low voltage. The increasedcurrent at low voltage also boosts luminous efficacy and reduced

distortion; hence, lower total harmonic distortion.

ac led drive technology

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