CPC9909

R03

www.ixysic.com

9

2.10 Linear Dimming

A linear dimming function can be implemented by

applying a DC control voltage to the LD pin. By varying

the current level in the LEDs which in turn will increase

or decrease the light intensity. The control voltage to

the LD pin can be generated from an external voltage

user requires LED current of a particular level, and

a voltage higher than the current sense threshold

voltage to the LD pin will not change the output current

due to the fixed internal threshold setting. When the

Figure 3 Typical Linear Dimming Application Circuit

2.11 PWM Dimming

Pulse width modulation dimming can be implemented

by driving the PWMD pin with a low frequency square

wave signal in the range of a few hundred Hertz. The

PWMD signal controls the LED brightness by gating

the PWM gate driver output pin GATE. The signal can

be generated by a microcontroller or a pulse generator

with a duty cycle proportional to the amount of desired

light output.

Figure 4 Buck Driver for PWM Dimming Application Circuit

2.12 Combination Linear and PWM Dimming

A combination of linear and PWM dimming techniques

can be used to achieve a large dimming ratio.

HB LEDs

350mA

D1

BYV26B

C1

0.1

μF

400V

C1

22

μF

400V

R1

402k

Ω

L1

4.7mH

R4

0.56

Ω

R2

51k

Ω

RA1

5.0k

Ω

C1

2.2

μF

16V

C1

0.1

μF

25V

AC

AC

+

-

BR1

Fuse F2

2A

NTC1

CPC9909

V

IN

CS

GND

GATE

R

T

LD

V

DD

PWMD

IXTA8N50P

LD

Monitor

AC Input

90 - 265V

rms

HB LEDs

900mA Max

ASMT-Mx00

D1 Schottky

40V

0.1

μF

50V

402k

Ω

220

μH

R1

0.27

Ω

10

μF

50V

CPC9909

V

IN

CS

GND

GATE

R

T

LD

V

DD

PWMD

Q1

V

IN

12 - 30V

DC

PWM

CPC1001N*

*Optional Isolation