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APW7071CE-TUL

White LED DC/DC Step-Up Converter

Anpec Electronics 

APW7071

Application Information

Setup the LED current

The LED current is controlled by the reference

voltage and resistor and R1 shows in Figure 1. The

current through the LEDs is given by the 250mV/R1.

Brigtness control

a. By an adjustable DC voltage

Uses a DC voltage to control the feedback voltage.

As the DC voltage increases, current starts flowing

down R3, R2 and R1. The loop will continue to

regulate the feedback voltage at 250mV. Thus the

current has to decrease through the LEDs by the

same amount of current as is being injected from

the DC voltage source. With a VDC from 0V to 3.

3V, the resistor values shown for R2 and R3 can

control the LED current from 0mA to 20mA.

Vin

2.7V~6V

C1

4.7µF

D1

L1

MSCD052

4.7µH

6

VIN

1

SW

2

GND

5

OVP

C2

0.1µF

Vout

Vin

2.7V~6V

C1

4.7µF

D1

L1

MSCD052

4.7µH

6

VIN

SW 1

C2

0.1µF

2

GND

5

OVP

PWM 100Hz~300Hz

brightness

control

4

SHDN

Duty=100%, LED=20mA

Duty=0%, LED off

3

FB

Vout

R1

13

Fig. 4 Brightness Control by a PWM

signal apply to SHDN

c. By a filtered PWM signal

Brightness can be achieved by a filtered PWM

signal. The PWM signal above 5KHz is

recommended.

L1

Vin

D1

MSCD052

Vout

2.7V~6V

4.7µH

C1

4.7µF

6

VIN

1

SW

C2

0.1µF

2

GND

5

OVP

4

SHDN

3

R2

FB

10K

R3

120K

R1

13

Vadj=3.3V, LED off

Vadj=0V, LED=20mA

Fig. 3 Brightness Control by an

adjustable DC voltage

b. By a PWM signal apply to SHDN

The PWM signal is applied to the SHDN pin of

the APW7071. The LEDs will switch between full

load to completely shut off. The average current

through the LEDs will increase proportionally to

the duty cycle of the PWM signal. Due to the soft

start function, the PWM signal should be 100Hz

to 300Hz.

4

3

R2

SHDN

FB

PWM

3.3V

R3

10K

120K

R1

13

brightness

control

0V

R4

Duty=100%, LED off

10K

Duty=0%, LED=20mA

C3

0.1uF

Fig. 5 Brightness Control by

a filtered PWM signal

Copyright © ANPEC Electronics Corp.

9

Rev. A.1 - Feb., 2006

www.anpec.com.tw

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