
4
HV825
External Component Description
External Component
Selection Guide Line
Diode
Fast reverse recovery, 1N4148 or equivalent.
C
S
Capacitor
0.01 to 0.1
μ
F, 100V capacitor to GND is used to store the energy transferred from the inductor.
R
EL-osc
Resistor
The lamp frequency is controlled via the R
EL-osc
. The lamp frequency increases as the R
EL-osc
decreases.
As the lamp frequency increases, the amount of current drawn from the battery will increase and the output
voltage V
CS
will decrease. This is because the lamp will draw more current from V
CS
when driven at higher
frequencies.
In general, as the lamp size increases, larger R
EL-osc
is recommended to provide higher V
CS
. However, the
color of the lamp is dependent upon its frequency and the shade of the color will change slightly with different
frequencies.
R
SW-osc
Resistor
The switching frequency of the inductor is controlled via the R
SW-osc
. The switching frequency increases as
the R
SW-osc
decreases. As the switching frequency increases, the amount of current drawn from the battery
will decrease and the output voltage V
CS
will also decrease.
L
X
Inductor
The inductor L
X
is used to boost up the low input voltage. When the internal switch is on, the inductor is being
charged. When the internal switch is off, the charge in the inductor will be transferred to the high voltage
capacitor C
S
. The energy stored in the capacitor is connected to the internal H-bridge and therefore to the
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 R
SW-osc
)
should be increased to avoid saturation.
The test circuit uses a Murata (LQH4N561) 560
μ
H inductor. Using different inductor values or inductors from
different manufacturers will affect the performance.
As the inductor value decreases, smaller R
SW-osc
value shall be used. This will prevent inductor saturation.
Inductor with the same inductance value (560
μ
H) but lower series resistance will charge faster. The
R
SW-osc
resistor value needs to be decreased to prevent inductor saturation and high current consumption.
C
SW
Capacitor
A 1nF capacitor is recommended from R
SW-OSC
to GND. This capacitor is used to shunt any switching noise
that may couple into the R
SW-OSC
pin.
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100
FAX: (408) 222-4895
www.supertex.com
11/12/01
2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.