HV857X データシートの表示（PDF） - Supertex Inc

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HV857X

High Voltage EL Lamp Driver for Low Noise Applications

Supertex Inc 

HV857

External Component Description

External Component

Selection Guide Line

Diode

Fast reverse recovery diode, 150V Sanyo SB01-15 or equivalent.

Cs Capacitor

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

REL-osc

The EL lamp frequency is controlled via an external REL resistor connected between REL-osc and VDD of the

device. The lamp frequency increases as REL decreases. As the EL lamp frequency increases, the amount

of current drawn from the battery will increase and the output voltage VCS will decrease. The color of the EL

lamp is dependent upon its frequency.

A 2MΩ resistor would provide lamp frequency of 205 to 275Hz. Decreasing the REL-osc by a factor of 2 will

increase the lamp frequency by a factor of 2.

RSW-osc

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 RSW decreases. With a given inductor, as the switching

frequency increases, the amount of current drawn from the battery will decrease and the output voltage, VCS,

will also decrease.

Lx Inductor

The inductor Lx is used to boost the low input voltage by inductive flyback. When the internal switch is 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 CS. The energy stored in the capacitor is connected to the 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 switching frequency of the

inductor (controlled by RSW) should be increased to avoid saturation.

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

inductors with thesame inductance value but with lower series DC resistance, lower RSW value 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, (VIN x IIN), will also increase. If the input power is greater than the power

dissipation of the package (300mW), an external resistor in series with one side of the lamp is recommended

to help reduce the package power dissipation.

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