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HV857X

High Voltage EL Lamp Driver for Low Noise Applications

Supertex Inc 

HV857 Application Note

HV857

Application Note

AN-H43

HV857 EL Lamp Driver Circuits for Low Audible Noise or

High Brightness Applications

by Roshanak Aflatouni, Applications Engineer

This Application Note describes the method (patent pending) to

reduce the audible noise generated by an EL (Electrolumines-

cent) lamp used in mobile phone applications.

This Application Note also provides example circuits as a guide-

line for applications with different lamp sizes, input voltages, and

brightness requirements.

For additional assistance in designing EL driver circuits, please

refer to Application Notes AN-H33 (effect of external compo-

nents on performance of Supertex EL drivers), Lamp Driver

Circuits.

When constructing and testing one of the driver circuits listed

below, keep in mind that results may differ from those given due

to lamp characteristics and component tolerance.

When making component changes for circuit optimization, al-

ways remove supply voltages first. After making adjustments,

bring up the supply voltage slowly starting from the minimum

required device input voltage while monitoring input current. A

sharp rise in current usually indicates a saturated inductor. Use

a higher current rated inductor, a higher value inductor, or

increase conversion frequency by lowering RSW-OSC value.

Figure 1: Typical Application Circuit

ON=VDD

OFF=0

Enable Signal

+

VIN

VDD

1.0µF

1 VDD

VA 8

2 RSW-osc

VB 7

3 REL-osc

4 Gnd

CS 6

LX 5

HV857MG

Series R

EL Lamp

SB01-15

LX

CS

Sanyo Diode SB01-15CP

11/27/01

Supertex Inc. does not recommend the use of its products in life support applications and will not knowingly sell its products for use in such applications unless it receives an adequate "products liability

indemnification insurance agreement." Supertex does not assume responsibility for use of devices described and limits its liability to the replacement of devices determined to be defective due to

workmanship. No responsibility is assumed for possible omissions or inaccuracies. Circuitry and specifications are subject to change without notice. For the latest product specifications, refer to the

Supertex website: http://www.supertex.com. For complete liability information on all Supertex products, refer to the most current databook or to the Legal/Disclaimer page on the Supertex website.

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