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8
Document Number 83622
Rev. 1.4, 26-Oct-04
VISHAY
IL300
Vishay Semiconductors
Application Considerations
In applications such as monitoring the output voltage
from a line powered switch mode power supply, mea-
suring bioelectric signals, interfacing to industrial
transducers, or making floating current measure-
ments, a galvanically isolated, DC coupled interface
is often essential. The IL300 can be used to construct
an amplifier that will meet these needs.
The IL300 eliminates the problems of gain nonlinear-
ity and drift induced by time and temperature, by mon-
itoring LED output flux.
A PIN photodiode on the input side is optically cou-
pled to the LED and produces a current directly pro-
portional to flux falling on it. This photocurrent, when
coupled to an amplifier, provides the servo signal that
controls the LED drive current.
The LED flux is also coupled to an output PIN photo-
diode. The output photodiode current can be directly
or amplified to satisfy the needs of succeeding cir-
cuits.
Isolated Feedback Amplifier
The IL300 was designed to be the central element of
DC coupled isolation amplifiers. Designing the IL300
into an amplifier that provides a feedback control sig-
nal for a line powered switch mode power is quite sim-
ple, as the following example will illustrate.
See Figure 17 for the basic structure of the switch
mode supply using the Infineon TDA4918 Push-Pull
Switched Power Supply Control Chip. Line isolation
and insulation is provided by the high frequency
transformer. The voltage monitor isolation will be pro-
vided by the IL300.
Figure 12. Amplitude Response vs. Frequency
Figure 13. Amplitude and Phase Response vs. Frequency
Figure 14. Common-Mode Rejection
iil300_12
10 4
10 5
10 6
5
0
-5
-10
-15
-20
F - Frequency - Hz
Amplitude
Response
-
d
B
RL=1.0 Kˇ
RL=10 Kˇ
IF=10 mA, Mod = ±2.0 mA (peak)
iil300_13
dB
PHASE
-
Phase
Response
-
°
103
104
105
106
107
5
0
-5
-10
-15
-20
45
0
-45
-90
-135
-180
F - Frequency - Hz
Amplitude
Response
-
d
B
IFq=10 mA
Mod= ±4.0 mA
TA=25°C
RL=50
iil300_14
10
100
1000
10000
100000 1000000
-130
-120
-110
-100
-90
-80
-70
-60
F - Frequency - Hz
CMRR
-
R
ejection
Ratio
-
d
B
Figure 15. Photodiode Junction Capacitance vs. Reverse Voltage
iil300_15
0
2
4
6
8
10
12
14
Voltage - Vdet
Capacitance
-
p
F
024
6
8
10