1
HV857
11/14/01
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.
HV857
High Voltage EL Lamp Driver for
Low Noise Applications
Features
Patent pending audible noise reduction
Patent pending lamp aging compensation
190V
PP
output voltage for higher brightness
Patented output timing for high efficiency
Single cell lithium ion compatible
150nA shutdown current
Wide input voltage range 1.8V to 5.0V
Separately adjustable lamp and converter frequencies
Output voltage regulation
Split supply capability
Applications
LCD backlighting
Mobile cellular phones
PDAs
Handheld wireless communication products
Global Positioning Systems (GPS)
General Description
The Supertex HV857 is a high voltage driver designed for driving
Electroluminescent (EL) lamps of up to 5 square inches. The
input supply voltage range is from 1.8V to 5.0V. The device uses
a single inductor and a minimum number of passive components.
The nominal regulated output voltage that is applied to the EL
lamp is
±
95V. The chip can be enabled/disabled by connecting
the resistor on R
sw-osc
to V
DD
/ground.
The HV857 has two internal oscillators, a switching MOSFET,
and a high voltage EL lamp driver. The frequency for the
switching MOSFET is set by an external resistor connected
between the R
sw-osc
pin and the supply pin V
DD
. The EL lamp
driver frequency is set by an external resistor connected be-
tween R
EL-osc
pin and the V
DD
pin. An external inductor is
connected between the L
X
and V
DD
pins or V
IN
for split supply
applications. A 0.003-0.1
µ
F capacitor is connected between C
s
and ground. The EL lamp is connected between V
A
and V
B
.
The switching MOSFET charges the external inductor and
discharges it into the capacitor at C
s
. The voltage at C
s
will start
to increase. Once the voltage at C
s
reaches a nominal value of
95V, the switching MOSFET is turned OFF to conserve power.
The outputs V
A
and V
B
are configured as an H bridge and are
switching in opposite states to achieve
±
95V across the EL lamp.
Typical Application
EL Lamp
+
_
C
S
1
2
3
4
8
6
5
HV857MG
7
V
DD
=V
IN
V
DD
R
SW-osc
R
EL-osc
Gnd
L
X
C
S
V
B
V
A
L
X
C
IN
Regulated Voltage=V
DD
Enable Signal
ON=V
DD
OFF=0
2
HV857
Symbol
Parameter
Min
Typ
Max
Units
Conditions
R
DS(on)
On-resistance of switching transistor
6.0
I=100mA
V
Cs
Max. output regulation voltage
85
95
105
V
V
DD
=1.8V to 5.0V
V
A
V
B
Peak to Peak output voltage
170
190
210
V
V
DD
=1.8V to 5.0V
I
DDQ
Quiescent V
DD
supply current
150
nA
R
SW-OSC
=Low
I
DD
Input current going into the V
DD
pin
150
µ
A
V
DD
=1.8V to 5.0V. See Figure 1.
I
IN
Input current including inductor current
20
25
mA
See Figure 1.*
V
Cs
Output voltage on V
Cs
84
V
See Figure 1.
f
EL
EL lamp frequency
205
240
275
Hz
See Figure 1.
f
SW
Switching transistor frequency
80
KHz
See Figure 1.
D
Switching transistor duty cycle
88
%
See Figure 1.
* The inductor used is a 220
µ
H Murata inductor, max DC resistance of 8.4
, part # LQH32CN221K21.
Electrical Characteristics
DC Characteristics
(Over recommended operating conditions unless otherwise specified, T
A
=25
°
C)
Symbol
Parameter
Min
Typ
Max
Units
Conditions
V
DD
Supply voltage
1.8
5.0
V
f
EL
Output drive frequency
1
KHz
T
A
Operating temperature
-40
85
°
C
Recommended Operating Conditions
Symbol
Parameter
Min
Typ
Max
Units
Conditions
EN-L
Logic input low voltage
0
0.2
V
V
DD
=1.8V to 5.0V
EN-H
Logic input high voltage
V
DD
-0.2
V
DD
V
V
DD
=1.8V to 5.0V
Enable/Disable Function Table
Absolute Maximum Ratings*
Supply Voltage, V
DD
-0.5V to +6.5V
Operating Temperature Range
-40
°
to +85
°
C
Storage Temperature Range
-65
°
C to +150
°
C
MSOP-8 Power Dissipation
300mW
Output voltage, V
CS
-0.5 to +120V
Note:
*Absolute Maximum Ratings are those values beyond which damage to the device
may occur. Functional operation under these conditions is not implied. Continu-
ous operation of the device at the absolute rating level may affect device reliability.
All voltages are referenced to device ground.
Package Options
Device
MSOP-8
Die
HV857
HV857MG*
HV857X
* Product supplied on 2500 piece carrier tape reels.
Ordering Information
Pin Configuration
V
DD
V
A
R
SW
V
B
R
EL
C
S
Gnd
L
X
1
2
3
4
8
7
6
5
MSOP-8
Top View
3
HV857
Block Diagram
Switch
Osc
C
+
_
Vref
Disable
High
Voltage
Level
Trans-
lators
GND
V
DD
Q
Q
Q
V
A
C
S
L
X
V
B
Q
R
SW
Rel
Vsen
EL
Osc
V
DD
Figure 1: Typical Application/Test Circuit
Device
Lamp Size
V
IN
I
IN
V
CS
f
EL
Brightness
HV857MG
3.0 in
2
3.3V
20mA
84V
240Hz
6.0ft-lm
Typical Performance
10nF
+
_
3.3nF
100V
1
2
3
4
8
6
5
HV857MG
7
V
IN
V
DD
R
SW-osc
R
EL-osc
Gnd
L
X
C
S
V
B
V
A
220
µH
SB01-15
1.0
µF
2.0M
V
DD
Enable Signal
ON=V
DD
OFF=0
V
IN
=V
DD
L
X
=220
µH Murata (LQH32CN221K21)
SB01-15=150V Sanyo Diode
2.0K
Equivalent to 3.0in
2
lamp
4
HV857
Iin, Vcs, Brightness vs Inductor Value
0
10
20
30
40
50
60
70
80
90
100
100
200
300
400
500
600
Inductor Value (µH)
0
1
2
3
4
5
6
7
Iin
Brightness
Vcs
Iin vs Vin
13
15
17
19
21
23
25
1.5
2.5
3.5
4.5
5.5
Vin (V)
Typical Performance Curves for Figure 1
(EL Lamp=3.0in
2
, V
DD
=3.0V)
V
CS (
V)
lin
(
mA)
Brightness
(ft-lm
)
lin
(
mA)
lin
(
mA), V
CS
(V)
Brightness
(ft-lm
)
Brightness vs Vin
1
2
3
4
5
6
7
1.5
2.5
3.5
4.5
5.5
Vin (V)
Iin vs Vcs
14
16
18
20
22
24
55
65
75
85
95
Vcs (V)
Vcs vs Vin
55
65
75
85
95
1.5
2.5
3.5
4.5
5.5
Vin (V)
150
250
350
450
550
lin
5
HV857
External Component Description
External Component
Selection Guide Line
Diode
Fast reverse recovery diode, 150V Sanyo SB01-15 or equivalent.
Cs Capacitor
0.003
µ
F to 0.1
µ
F, 100V capacitor to GND is used to store the energy transferred from the inductor.
R
EL-osc
The EL lamp frequency is controlled via an external R
EL
resistor connected between R
EL-osc
and V
DD
of the
device. The lamp frequency increases as R
EL
decreases. As the EL lamp frequency increases, the amount
of current drawn from the battery will increase and the output voltage V
CS
will decrease. The color of the EL
lamp is dependent upon its frequency.
A 2M
resistor would provide lamp frequency of 205 to 275Hz. Decreasing the R
EL-osc
by a factor of 2 will
increase the lamp frequency by a factor of 2.
R
SW-osc
The switching frequency of the converter is controlled via an external resistor, R
SW
between R
SW-osc
and V
DD
of the device. The switching frequency increases as R
SW
decreases. With a given inductor, as the switching
frequency increases, the amount of current drawn from the battery will decrease and the output voltage, V
CS
,
will also decrease.
Lx Inductor
The inductor L
x
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 C
S
. 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 R
SW
) should be increased to avoid saturation.
220
µ
H Murata (LQH32CN221) inductors with 8.4
series DC resistance is typically recommended. For
inductors with thesame inductance value but with lower series DC resistance, lower R
SW
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, (V
IN
x I
IN
), 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.
6
HV857
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100 · FAX: (408) 222-4895
www.supertex.com
11/14/01rev.10
©2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
Split Supply Configuration
The HV857 can also be used for handheld devices operating
from a battery where a regulated voltage is available. This is
shown in Figure 2. The regulated voltage can be used to run
the internal logic of the HV857. The amount of current neces-
sary to run the internal logic is 150
µ
A Max at a V
DD
of 3.0V.
Therefore, the regulated voltage could easily provide the
current without being loaded down.
Figure 2: Split Supply and Enable/Disable Configuration
Enable/Disable Configuration
The HV857 can be easily enabled and disabled via a logic control
signal on the R
SW
and R
EL
resistors as shown in Figure 2 below.
The control signal can be from a microprocessor. R
SW
and R
EL
are typically very high values. Therefore, only 10's of microam-
peres will be drawn from the logic signal when it is at a logic high
(enable) state. When the microprocessor signal is high the
device is enabled and when the signal is low, it is disabled.
EL Lamp
+
_
C
S
1
2
3
4
8
6
5
HV857MG
7
Battery Voltage=V
IN
V
DD
R
SW-osc
R
EL-osc
Gnd
L
X
C
S
V
B
V
A
L
X
C
IN
Regulated Voltage=V
DD
Enable Signal
ON=V
DD
OFF=0
7
HV857 Application Note
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.
HV857
Application Note
AN-H43
HV857 EL Lamp Driver Circuits for Low Audible Noise or
High Brightness Applications
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.
by Roshanak Aflatouni, Applications Engineer
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 R
SW-OSC
value.
Figure 1: Typical Application Circuit
EL Lamp
+
C
S
1
2
3
4
8
6
5
HV857MG
7
V
IN
V
DD
R
SW-osc
R
EL-osc
Gnd
L
X
C
S
V
B
V
A
L
X
SB01-15
1.0
µF
V
DD
Enable Signal
ON=V
DD
OFF=0
Sanyo Diode SB01-15CP
Series R
8
HV857 Application Note
Mobile Phone Circuit for Audible Noise Reduction:
1
The following table provides EL lamp audible noise and brightness for circuits which were designed based on typical EL lamp sizes for
Mobile phone applications. See Figure 1, Table 3.
t
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1
How to Minimize EL Lamp
Audible Noise:
The EL lamp, when lit, generates an audible noise. This is due
to EL lamp construction which creates a major problem for
applications where the EL lamp can be close to the ear such as
cellular phones. The noisiest waveform is a square wave and the
quietest waveform has been assumed to be a sine wave.
After extensive research, Supertex has developed a waveform
that is quieter than a sine wave. The waveform takes the shape
of approximately 2RC time constants for rising and 2RC time
constants for falling, where the C is the capacitance of the lamp
and R is the external resistor used in series with one side of the
lamp. This waveform has been proven to generate less noise
than a sine wave.
The audible noise from the EL lamp can be set at a desired level
based on the series resistor value used with the lamp. We have
chosen two commonly used lamp sizes for the mobile phones to
demonstrate the effect of series resistor on the audible noise
generated by the EL lamp. It is important to note that use of this
resistor will reduce the voltage across the lamp. Reduction of
voltage across the lamp will also has another effect on the overall
performance of the Supertex EL drivers, age compensation
(patent pending). This addresses a very important issue. EL
lamp life is an important design concern to mobile phone
manufacturers.
As an EL lamp ages, its brightness is reduced and its capacitance
is diminished. By using the RC model to reduce the audible noise
generated by an EL lamp, the voltage across the lamp will
increase as its capacitance diminishes. Hence the increase in
voltage will compensate for the reduction of the brightness. As a
result, it will extend an EL lamp's half-life (half the original
brightness).
Effect of Series Resistor on EL
Lamp Audible Noise and
Brightness:
Increasing the value of the series resistor with the lamp will
reduce the audible noise of an EL lamp as well as its brightness.
This is due to the fact that the output voltage across the lamp will
be reduced and the output waveform will have rounder edges.
Note: 1. All values are nominal.
Table 1
9
HV857 Application Note
Circuit 1
Circuit 2
10
15
20
25
30
35
40
0
20
40
60
80
100
120
140
160
Series R (K
)
Lamp Noise (dB)
Lamp Noise vs. Series R (2.6in
2
EL Lamp)
0
5
10
15
20
25
30
0
20
40
60
80
100
120
140
160
Series R (K
)
Brightness (cd/m
2
)
Brightness vs. Series R (2.6in
2
EL Lamp)
Lamp Noise (dB)
10
15
20
25
30
35
40
0
20
40
60
80
100 120 140 160
Series R (K
)
Brightness vs. Series R (1.7in
2
EL Lamp)
Brightness (cd/m
2
)
Lamp Noise vs. Series R (1.7in
2
EL Lamp)
0
5
10
15
20
25
0
20
40
60
80
100 120 140 160
Series R (K
)
10
HV857 Application Note
Typical HV857 Output waveform Before and After Noise Reduction:
The following are actual scope pictures, which show the differential output waveform across the lamp, audible noise, and lamp light output
for circuits 1 and 2.
Circuit 1
Series R=0
Series R=65K
Light Output
Audible Noise
Differential Output Waveform
across the lamp
100V/div
50mV/div
200mV/div
1ms/div
Light Output
Audible Noise
Differential Output Waveform
across the lamp
100V/div
50mV/div
200mV/div
1ms/div
11
HV857 Application Note
Circuit 2
Series R=0
1ms/div
Light Output
Audible Noise
Differential Output Waveform
across the lamp
100V/div
20mV/div
200mV/div
Series R=55K
1ms/div
Light Output
Audible Noise
Differential Output Waveform
across the lamp
100V/div
20mV/div
200mV/div
12
HV857 Application Note
Audible Noise Measurement Setup:
The following setup was used to collect EL lamp audible noise data. An Oscilloscope/Spectrum analyzer was used to observe the
differential output waveform, audible noise level (in mV), and light output (in mV) of the EL lamp. The EL lamp is placed in the anechoic
chamber and a condenser microphone is placed 10mm away from the surface of the EL lamp.
Oscilloscope/Spectrum
Analyzer
Soundproof Anechoic Chamber
Opto-acoustic
Probe
EL Lamp
10mm
Signal Conditioner
Headphones
Low pass
filter
Scaling
A-weighting
filter
EL
Driver
DC
Supply
10:1 probes
Scaling
-
+
Pneumatic
Supports
Drawing not to scale
Opto-acoustic probe is battery powered
to minimize electrical noise.
NC
NC
Driver Measurement Test Setup
13
HV857 Application Note
Circuit Selector Guide for Non Audible Noise Sensitive Applications:
1
(Handheld products, PDAs, GPS, 2-way pagers, MP3)
No series resistor is used for the following circuits (R=0
). Also see Figure 1 and Table 3.
External components used for Circuits 1 to 9:
The following table provides the value for external components used in Figure 1. The manufacturer and part number for the inductor is
also provided. If other value inductors are used, the circuit will need to be reoptimized.
t
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1
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2
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3
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3
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3
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9
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V
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8
1
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7
5
3
4
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4
4
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4
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3
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3
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4
A
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7
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1
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3
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3
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4
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m
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3
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0
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p
-
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p
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5
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6
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5
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6
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.
3
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3
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m
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8
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3
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7
7
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6
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5
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3
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5
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7
.
4
4
3
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6
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3
.
3
V
3
.
3
A
m
2
.
1
2
p
-
p
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8
6
1
z
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0
6
1
t
i
u
c
r
i
C
r
o
t
c
u
d
n
I
x
L
R
C
S
O
-
W
S
R
C
S
O
-
L
E
C
S
r
o
t
i
c
a
p
a
C
e
u
l
a
V
,
r
e
r
u
t
c
a
f
u
n
a
M
.
o
N
.
t
r
a
P
e
u
l
a
V
e
p
y
T
1
H
µ
0
2
2
,
a
t
a
R
u
M
1
2
K
1
2
2
N
C
2
3
H
Q
L
K
0
6
5
M
0
.
2
F
n
3
.
3
O
P
N
2
H
µ
0
2
2
a
t
a
R
u
M
1
2
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1
2
2
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C
2
3
H
Q
L
K
0
6
5
M
0
.
2
F
n
3
.
3
O
P
N
3
H
µ
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2
,
a
t
a
R
u
M
1
2
K
1
2
2
N
C
2
3
H
Q
L
K
0
6
5
M
5
.
1
F
n
3
.
3
O
P
N
4
H
µ
0
2
2
,
a
t
a
R
u
M
1
2
K
1
2
2
N
C
2
3
H
Q
L
K
0
3
3
M
3
.
3
F
n
3
.
3
O
P
N
5
H
µ
0
2
2
,
a
t
a
R
u
M
1
2
K
1
2
2
N
C
2
3
H
Q
L
K
0
6
5
M
0
.
1
F
n
3
.
3
O
P
N
6
H
µ
0
2
2
,
a
t
a
R
u
M
1
2
K
1
2
2
N
C
2
3
H
Q
L
K
0
6
5
M
0
.
2
F
n
3
.
3
O
P
N
7
H
µ
0
2
2
,
a
t
a
R
u
M
1
2
K
1
2
2
N
C
2
3
H
Q
L
K
0
6
5
M
0
.
2
F
n
3
.
3
O
P
N
8
H
µ
0
2
2
,
a
t
a
R
u
M
1
0
K
1
2
2
N
M
3
4
H
Q
L
K
0
6
5
M
0
.
2
F
n
3
.
3
O
P
N
9
H
µ
0
2
2
,
a
t
a
R
u
M
1
0
K
1
2
2
N
M
3
4
H
Q
L
K
0
6
5
M
3
.
3
F
n
3
.
3
O
P
N
Note: 1. All values are nominal. Lamp brightness and current draw can vary by type and manufacturer.
Table 2
Table 3
14
HV857 Application Note
1235 Bordeaux Drive, Sunnyvale, CA 94089
TEL: (408) 744-0100 · FAX: (408) 222-4895
www.supertex.com
11/27/01AppNote.rev.3
©2001 Supertex Inc. All rights reserved. Unauthorized use or reproduction prohibited.
L
X
Inductor Selection:
Different inductor values and/or from different manufacturers
can be used in place of what is shown. However, the circuit will
need to be reoptimized by changing the R
SW-OSC
value. Smaller
R
SW-OSC
value needs to be used for inductors with lower series
resistance. Lower amount of current will be drawn when using
larger value inductors. But, for the same R
SW-OSC
value, a lower
amount of energy will be transferred due to the higher series
resistance of a larger value inductor. Hence, when larger value
inductors with higher series resistance are used, the R
SW-OSC
value needs to be increased. It is very important to make a note
of the saturation current of the inductor. If the saturation current
of the inductor is lower than what the circuit/application requires,
the inductor and/or IC will be damaged.
C
S
Capacitor Selection:
Different C
S
Capacitor types and value can be used in place of
what is shown in circuits 1 to 9. However, the use of a different
C
S
Capacitor type will generate audible noise due to the piezo
electric effect of materials used for their structure (such as X7R
and 5YU capacitors).
A different value capacitor can be used. A larger value C
S
Capacitor (10nF) is recommended to be used for larger EL lamps
and/or larger input voltage range. A smaller value C
S
Capacitor
can be used as long as the over all efficiency of the circuit is not
decreased. When using a smaller value C
S
Capacitor, the circuit
will need to be reoptimized by using a smaller R
SW-OSC
value.
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