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參數(shù)資料
| 型號： | SP4439 |
| 英文描述： | Ultra-Quiet Electroluminescent Lamp Driver with Programmable Wave Shape(超靜場致發(fā)光燈驅(qū)動器（可編程波形）) |
| 中文描述： | 超靜音電致發(fā)光燈帶可編程波形（超靜場致發(fā)光燈驅(qū)動器（可編程波形）驅(qū)動程序） |
| 文件頁數(shù)： | 7/13頁 |
| 文件大?。?/td> | 193K |
| 代理商： | SP4439 |
7
Rev. 2/15/01 SP4439 Ultra-Quiet Electroluminescent Lamp Driver With Programmable Waveshape Copyright 2000 Sipex Corporation
a lamp from the lamp manufacturer that will be
used in production. The following examples
assume the nominal lamp frequency is set to
250Hz. This defines a rise-time of 800uS.
Example 1- Lamp Size = 2in
(12.9cm
2
):
A typical 2in
2
(12.9cm
2
) lamp has a capacitance
of 8nF. Given the typical output peak voltage of
80V, the charge resistor can be calculated using
equation 4.
C
V
BIASC
x
T
C
x
C
EL
4
R
C
= (2.8V x 500uS) / (80V x 8nF) = 2188 Ohms
Example 2- Lamp Size = 4in
2
(25.8cm
2
):
If we assume the lamp capacitance doubles in
16nF then:
R
C
= (2.8V x 500uS) / (80V x 16nF) = 1094 Ohms
R
D
= (1.4V x 500uS) / (80V x 16nF) = 547 Ohms
Notes:
If the factors such as peak voltage and lamp
frequency are different, adjustment must be made
to those values in the resistance equations. There
are limitations to what the waveform will look
like. For example if the resistors are set small,
the times become fast and a step will appear at
the zero crossing point of the waveform. The
intent of the waveform programmability is to
allow the use of a wide range of lamp sizes while
maintaining a smooth waveform to minimize
audible noise.
Keep in mind that coil values and the oscillator
frequency may have to be changed to support a
given luminance for a particular lamp size. It is
best to define these parameters first and then go
back and calculate the charge and discharge
resistors.
Audio Noise Considerations:
A system can have different sources of audio
noise, The coil the filter capacitor, and the EL
lamp itself may be a source of audio noise if
operated in the audio frequency range.
Designers should select either the coil or coil
frequency such that the coil is not in continous
mode as this will greatly decrease efficiency and
contribute to noise.
This simply means that for a rise-time
measurement of 400
μ
s, the full-scale time is
500uS.
The ultimate goal here is to calculate the values
for the charge and discharge resistors R
C
and R
D
respectively. These two resistors define a constant
charge current I
C
and discharge current I
D
. The
combination of the lamp capacitance and the
constant charge currents results in the rise and
fall waveform lamps. Lets start by calculating
the constant currents.
The charge current is defined as:
I
C
=
V
BIASC
Where: V
BIASC
is defined internally to be 2.8V.
R
C
The charge current is defined as:
I
C
= V
BIASD
Where: V
BIASD
is defined internally to be 1.4V.
R
D
The charge and discharge currents should be
equal to give smooth rise and fall times. Once the
currents are known, the charge and discharge
time is defined by:
T
=
V
Where: C
EL
is the lamp capacitance,
I
C,D
and
V
is the outpeak voltage.
Subsituting equations 1 or 2 into equation 3 gives
the equation to calculate the charge resistor
directly:
T = C
T
=
V x R
C
,
R
C
=
V x R
C
V
BIASC EL
V
BIAS
V x C
EL
R
C
inductance of the coil. When the NPN transistor
switch is off, the energy is forced through an
internal diode which drives the switched H-
bridge network. This energy recovery is directly
related to the brightness of the EL lamp output.
There are many variations among coils; magnetic
material differences, winding differences and
parasitic capacitances.
The proper way to approach the SP4493 system
design is to first measure the capacitance of the
lamp intended for the application. The
capacitance of an EL lamp is proportional to the
area of the lamp. Lamps from different
manufacturers will exhibit different capacitance/
area values. Therefore it is important to measure
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