ZXSC410/ZXSC420/ZXSC440

Document number: DS33618 Rev. 5 - 2

9 of 17

www.diodes.com

March 2013

© Diodes Incorporated

ZXSC410/ZXSC420/ZXSC440

Dimming Control

There are many types of dimming control that can be implemented for the ZXSC410/420/440.

Dimming Control Using the Shutdown Pin

The first method uses the shutdown pin (only ZXSC410 and

ZXSC440). By injecting a PWM waveform on this pin and varying the

duty cycle, LED current and hence LED brightness can be adjusted.

To implement this method of brightness control on the ZXSC410/440,

frequency of 120Hz or above (to eliminate LED flicker) should be

applied to the STDN pin. The LED current and hence LED brightness

is linearly proportional to the duty cycle ratio, so for brightness control

adjust duty cycle ratio as necessary. For example, a 10% duty cycle

equates to 10% of full LED brightness.

30

0

10

20

40

20

0

100

80

60

DUTY CYCLE (%)

LED Current vs. Duty Cycle

4 White LEDs

V = V

= 3.3V

IN

EN

Dimming Control Using a DC Voltage

pin.

By adding resistors R2 and R3 and applying a DC voltage, the LED

current can be adjusted from 100% to 0%. As the DC voltage

increases, the voltage drop across R2 increases and the voltage drop

across R1 decreases, thus reducing the current through the LEDs.

Selection of R2 and R3 should ensure that the current from the

DC

voltage is much less than the LED current and much larger than the

feedback current. The component values in the diagram above

represent 0% to 100% dimming control from a 0 to 2V DC voltage.

R2

10k

R3

67k

R1

Dimming Control Using a Filtered PWM Signal

The filtered PWM signal can be considered as an adjustable

DC voltage by applying a RC filter (R4 and C1). The values

shown in the diagram below are configured to give 0% to

100% dimming for a 1kHz to 100kHz PWM signal with a 2V

amplitude. e.g. a 50% duty cycle will give 50% dimming.

C1

0.1µF

R2

10k

R3

67k

R1

PWM

R4

10k