TK65920 Ver la hoja de datos (PDF) - Toko America Inc

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Fabricante

TK65920

MEDIUM EL LAMP DRIVER

Toko America Inc  

TK6592x

THEORY OF OPERATION

An Electroluminescent (EL) Lamp is a strip of plastic,

coated with a phosphorous material that emits light when

a high voltage AC signal is applied to the terminals of the

device. EL panels have the ability to light the entire panel

uniformly. Because of this, they are gradually becoming

more popular and widespread than LEDs. The amount of

light emitted from an EL Lamp is typically proportional to

the magnitude of the voltage applied to the lamp.

Furthermore, the color of the light emitted by an EL Lamp

is somewhat dependent upon the frequency of the applied

drive signal. For most applications, a peak-to-peak voltage

of 100 to 170 V, with a drive frequency of 175 to 400 Hz,

provides optimal trade-off between lamp intensity and

power consumption.

The capacitance of the EL Panel is typically proportional to

the size of the lamp (a 1 square inch EL Panel typically

exhibits approximately 5 nF of capacitance load). The

TK6592x series of devices has been optimized to drive EL

panels, which are approximately 2-4 square inches in size.

The Boost section of the TK6592x consists of a controller

for stepping up a relatively low voltage (2.7 to 6 V) to a

much higher voltage (50 to 90 V) needed to drive the EL

Lamp. The boost section of the TK6592x uses a proprietary

architecture which provides a relatively constant output

power, independent of the input supply, without the need

for sensing the high voltage output of the boost converter.

By controlling the peak current through the switching

element of the boost converter, the boost section provides

a constant output power independent of the input supply.

The H-Bridge section of the TK6592x switches the high

voltage output of the boost converter to the two terminals

of the EL Lamp. By alternately switching the terminals of

the lamp between the high voltage supply and ground, the

peak-to-peak voltage developed across the lamp is

effectively twice the high voltage generated by boost

converter. Furthermore, the TK6592x limits the magnitude

of the drive currents through the H-Bridge switches in

order to minimize the edge rates developed across the EL

Lamp. This approach protects the EL Panel from large

current spikes and reduces the likelihood of high frequency

noise components being injected into neighboring circuitry.

The Oscillator section of the TK6592x generates a fixed

frequency clock source for the previously described Boost

and H-Bridge sections, without the need for external

components. The high frequency output of the oscillator is

used for driving the boost controller. A lower frequency

clock is generated by dividing the high frequency clock by

128; this lower frequency clock corresponds to the drive

frequency of the EL Lamp. The laser-trimmed oscillators

are relatively insensitive to variations in temperature and

supply voltage. Therefore, they provide good control of the

lamp color emitted by the panel.

The circuit below illustrates a typical application where the

TK6592x is driving a 2-square-inch EL Lamp with a

capacitance of approximately 12 nF.

CEL

12 nF

EL +

HV

EL -

VCC

VIN

GND

IND

L1

C1

D1

47 nF

FIGURE 1: TYPICAL APPLICATION

By keeping the ratio of the boost frequency and the H-

Bridge frequency constant, the peak-to-peak output voltage

from the TK6592x becomes primarily dependent upon the

capacitance of the EL Lamp, the peak current threshold of

the boost converter, and the value of the inductive element

used in the boost converter. For the TK6592x, the peak

current threshold is laser-trimmed to 52 mA. The capacitive

load of the EL Lamp is a function of panel size and is

typically fixed. Therefore, the high voltage output of the

boost converter can be set to a desired voltage by selecting

the appropriate value of the inductive element used in the

boost converter.

IPEAK = Boost Peak Current Threshold (52 mA)

CEL = Capacitance of EL Lamp

L = Inductance Value

VHV = (IPEAK / 2) x (L /CEL) x 128

May 2000 TOKO, Inc.

Page 9

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