SP4428DS/16

SP4428 Electroluminescent Lamp Driver

© Copyright 2000 Sipex Corporation

3

THEORY OF OPERATION

The SP4428 is made up of three basic circuit

elements, an oscillator, coil, driver and switched

H-bridge network. The oscillator provides the

device with an on-chip clock source used to control

the charge and discharge phases for the coil and

lamp. An external capacitor connected between

pins 1 and V

frequency. For a given choice of coil inductance

there will be an optimum C

gives the maximum light output in a given lamp.

The suggested oscillator frequency is 28.8kHz

(C

divided to create the control signal f

The oscillator output is internally divided down

by 6 flip flops, a 28.8kHz signal will be divided

into 6 frequency levels; 14.4kHz, 7.2kHz, 3.6kHz,

1.8kHz, 900Hz, and 450Hz. The oscillator output

(28.8kHz) is used to drive the coil (see figure 2 on

page 7) and the sixth flip flop output (300Hz) is

used to drive the lamp. Although the oscillator

frequency can be varied to optimize the lamp

output, the ratio of f

The coil is an external component connected from

V

developed in the coil according to the equation

E

I=(V

PIN DESCRIPTION

Pin 1 – C

set Oscillator frequency.

Pin 2 – V

ground.

Pin 3 – Coil- Coil input, connect coil from

V

Pin 4 – D1- Diode cathode connection.

Pin 5 – EL2- Lamp driver output1, connect to

EL lamp.

Pin 6 – EL1- Lamp driver output2, connect to

EL lamp.

Pin 7 – V

system V

Pin 8 – HON- Enable for driver operation,

high = active; low = inactive.

1

2

3

4

8

7

6

5

SP4428 Schematic

Q

Q

HON

SCR1

SCR2

OSC

FF1

FF6

EL Lamp

1M

Ω

Coil

5

6

EL1

EL2

1

Cap1

2

7

3

470

µH/4.9Ω

8

180pF

IN4148

Optional

1,800pF

4

D1

.1

µF