6

HV860

Figure 4: PWM Dimming Circuit

HV860

EL Lamp

3.3nF

200V

0.1μF

1.0MΩ

4.7μF

BAS21

2.0MΩ

3.3MΩ

220μH

(Cooper Inductor SD3814-221)

9

7

5

3

2

10

12

1

11

4

8

10kΩ

Open Drain

n-channel

PWM Signal

+

-

On = 1.5V

Off = 0V

+

-

VDD

VB

VA

CS

LX

VREF

VREG

REL-Osc

RSW-Osc

EN

GND

This section describes the method of dimming the EL lamp.

Reducing the voltage amplitude at the VREG pin will reduce

the voltage on the CS pin, which will effectively reduce the

peak to peak voltage the EL lamp sees. Figure 4 shows a

circuit to dim the lamp by changing the duty cycle of a PWM

signal. A 10kΩ resistor is connected in series with a 3.3MΩ

resistor. An N-channel open drain PWM signal is used to pull

the 10kΩ resistor to ground. The effective voltage on the

VREG pin will be proportional to the duty cycle of the PWM

signal. The PWM operating frequency can be anywhere

between 20kHz to 100kHz.

EL Lamp Dimming using PWM