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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

RL=1.0 KΩˇ

RL=10 KΩˇ

IF=10 mA, Mod = ±2.0 mA (peak)

iil300_13

dB

PHASE

103

104

105

106

107

5

0

-5

-10

-15

-20

45

0

-45

-90

-135

-180

F - Frequency - Hz

IFq=10 mA

Mod= ±4.0 mA

TA=25°C

RL=50 Ω

iil300_14

10

100

1000

10000

100000 1000000

-130

-120

-110

-100

-90

-80

-70

-60

F - Frequency - Hz

Figure 15. Photodiode Junction Capacitance vs. Reverse Voltage

iil300_15

0

2

4

6

8

10

12

14

Voltage - Vdet

024

6

8

10