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參數(shù)資料
| 型號： | SP4423 |
| 英文描述： | Electroluminescent Lamp Driver Low Power Applications |
| 中文描述： | 電致發(fā)光燈驅(qū)動器的低功耗應(yīng)用 |
| 文件頁數(shù)： | 4/13頁 |
| 文件大?。?/td> | 180K |
| 代理商： | SP4423 |
SP4423DS/14
SP4423 Electroluminescent Lamp Driver
4
Copyright 2000 Sipex Corporation
The on-chip oscillator of the
SP4423
can be
overdriven with an external clock source by
removing the C
capacitor and connecting a
clock source to pin 8 (Cap 2). The clock should
have a 50% duty cycle and range fromV
-1V to
ground. An external clock signal may be
desirable in order to synchronize any parasitic
switching noise with the system clock. The
maximum external clock frequencies that can
be supplied is 400kHz.
The coil is an external component connected from
V
to pin 3 of the
SP4423
. Energy is stored
in the coil according to the equation E
=1/2LI
2
,
where I is the peak current flowing in the inductor.
The current in the inductor is time dependent
and is set by the "ON" time of the coil switch:
I=(V
/L)t
, where V
is the voltage across the
inductor. At the moment the switch closes, the
current in the inductor is zero and the entire supply
voltage (minus the V
of the switch) is across the
inductor. The current in the inductor will then
ramp up at a linear rate. As the current in the
inductor builds up, the voltage across the inductor
will decrease due to the resistance of the coil and
the "ON" resistance of the switch: V
=V
-
IR
-V
. Since the voltage across the inductor is
decreasing, the current ramp-rate also decreases
which reduces the current in the coil at the end of
t
the energy stored in the inductor per coil cycle
and therefore the light output. The other important
issue is that maximum current (saturation current)
in the coil is set by the design and manufacturer of
the coil. If the parameters of the application such
as V
, L, RL or t
cause the current in the
coil to increase beyond its rated I
, excessive
heat will be generated and the power efficiency
will decrease with no additional light output. The
Sipex
SP4423
is final tested using a 20mH/70
coil from CTC. For suggested coil sources see
page 10
.
The supply V
can range from 2.2 to 6.0V. It is not
necessary that Vdd = V
. V
should not
exceed max coil current specification. The majority
of the current goes through the coil and is typically
much greater than I
DD
.
The f
signal controls a switch that connects
the end of the coil at pin 3 to ground or to open
circuit. The f
signal is a 75% duty cycle
signal, switching at 1/8 the oscillator frequency.
For a 64kHz oscillator f
is 8kHz. During the
time when the f
COIL
signal is high, the coil is
connected from V
to ground and a charged
magnetic field is created in the coil. During the
, the ground connection is
switched open, the field collapses and the
energy in the inductor is forced to flow toward
the high voltage H-bridge switches. f
will
send 16 of these charge pulses to the lamp, each
pulse increases the voltage drop across the lamp
in discrete steps. As the voltage potential
approaches its maximum, the steps become
shorter (see
Figure 1
on
page 9
).
The H-bridge consists of two SCR structures
that act as high voltage switches. These two
switches control the polarity of how the lamp is
charged. The SCR switches are controlled by
the f
signal which is the oscillator frequency
divided by 256. For a 64kHz oscillator,
f
LAMP
=250Hz.
When the energy from the coil is released, a high
voltage spike is created triggering the SCR
switches. The direction of current flow is
determined by which SCR is enabled. One full
cycle of the H-bridge will create 16 voltage
steps from ground to 80V (typical) on pins 4 and
5 which are 180 degrees out of phase with each
other (see
Figure 3
on
page 9
). A differential
representation of the outputs is shown in
Figure
4
on
page 9
.
To minimize AC interference it is
advisable to use a decoupling filter capacitor
between V
DD
and ground.
Electroluminescent Technology
What is electroluminescence
An EL lamp is basically a strip of plastic that is
coated with a phosphorous material which emits
light (fluoresces) when a high voltage (>40V)
which was first applied across it, is removed or
reversed. Long periods of DC voltages applied
to the material tend to breakdown the material
and reduce its lifetime. With these considerations
in mind, the ideal signal to drive an EL lamp is
a high voltage sine wave. Traditional approaches
to achieving this type of waveform included
discrete circuits incorporating a transformer,
transistors, and several resistors and capacitors.
This approach is large and bulky, and cannot be
implemented in most hand held equipment.
Sipex
now offers low power single chip driver circuits
specifically designed to drive small to medium
sized electroluminescent panels. All that is
required is one external inductor and capacitor.
相關(guān)PDF資料 |
PDF描述 |
|---|---|
| SP4423CN | Electroluminescent Lamp Driver Low Power Applications |
| SP4423CU | Electroluminescent Lamp Driver Low Power Applications |
| SP4423CX | Electroluminescent Lamp Driver Low Power Applications |
| SP4424 | Electroluminescent Lamp Driver Dual Oscillators |
| SP4424CN | Electroluminescent Lamp Driver Dual Oscillators |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SP4423CN | 制造商:Exar Corporation 功能描述:BALLAST/BACKLIGHT CONTROLLER/DRIVER, 8 Pin, Plastic, SOP |
| SP4423CU | 制造商:Exar Corporation 功能描述:BALLAST/BACKLIGHT CONTROLLER/DRIVER, 8 Pin, Plastic, TSSOP |
| SP4423CX | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Electroluminescent Lamp Driver Low Power Applications |
| SP4423NEB | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Electroluminescent Lamp Driver Low Power Applications |
| SP4423UEB | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Electroluminescent Lamp Driver Low Power Applications |
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