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Supertex inc.

www.supertex.com

Doc.# DSFP-HV857

A062013

HV857

External Component Description

External

Component

Description

Diode

Fast reverse recovery diode, BAS21 diode or equivalent.

C

0.003µF to 0.1µF, 100V capacitor to GND is used to store the energy transferred from the inductor.

R

The EL lamp frequency is controlled via an external R

of the device. The lamp frequency increases as R

the amount of current drawn from the battery will increase and the output voltage V

color of the EL lamp is dependent upon its frequency.

A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the R

of 2 will increase the lamp frequency by a factor of 2.

f

(2MΩ)(240Hz)

R

EL

R

The switching frequency of the converter is controlled via an external resistor, RSW between RSW-Osc

and VDD of the device. The switching frequency increases as R

the switching frequency increases, the amount of current drawn from the battery will decrease and the

output voltage, V

f

(560kΩ)(80Hz)

R

SW

L

The inductor L

on, the inductor is being charged. When the internal switch is off, the charge stored in the inductor will

be transferred to the high voltage capacitor C

internal H-bridge, and therefore to the EL lamp. In general, smaller value inductors, which can handle

more current, are more suitable to drive larger size lamps. As the inductor value decreases, the switch-

ing frequency of the inductor (controlled by R

A 220µH Murata (LQH32CN221) inductor with 8.4Ω series DC resistance is typically recommended. For

inductors with the same inductance value, but with lower series DC resistance, lower R

is needed to prevent high current draw and inductor saturation.

Lamp

As the EL lamp size increases, more current will be drawn from the battery to maintain high voltage

across the EL lamp. The input power, (V

the power dissipation of the package, an external resistor in series with one side of the lamp is recom-

mended to help reduce the package power dissipation.