Dimming Control
There are two different types of dimming control circuits:
1. Using a PWM Signal to EN Pin
With the PWM signal applied to the EN pin, the SE3506 is
turned on or off by the PWM signal. The LEDs operate at
either zero or full current. The average LED current
increases proportionally with the duty cycle of the PWM
signal. A 0% duty cycle will turn off the SE3506 and
corresponds to zero LED current. A 100% duty cycle
corresponds to full current. The typical frequency range of
the PWM signal is 1kHz to 5kHz. The magnitude of the
PWM signal should be higher than the minimum EN
voltage high. The switching waveforms of the EN pin PWM
control are shown below.
2. Using a DC Voltage
For some applications, the preferred method of
brightness control is a variable DC voltage to adjust
the LED current. The dimming control using a DC
voltage is shown below. As the DC voltage
increases, the voltage drop on R2 increases and
the voltage drop on R1 decreases. Thus, the LED
current decreases. The selection of R2 and R3 will
make the current from the variable DC source much
smaller than the LED current and much larger than
the FB pin bias current. For V
DC
range from 0V to
2V, the selection of resistors gives dimming control
of LED current from 0mA to 15mA.
Revision 12/4/2008
Preliminary and all contents are subject to change without prior notice
© Seaward Electronics, Inc., 2006. •
www.seawardinc.com.cn
• Page 4
SEAWARD [ Seaward Electronics Inc. ]
