IL300

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Vishay Semiconductors

Rev. 1.8, 02-Jun-14

2

Document Number: 83622

THIS DOCUMENT IS SUBJECT TO CHANGE WITHOUT NOTICE. THE PRODUCTS DESCRIBED HEREIN AND THIS DOCUMENT

OPERATION DESCRIPTION

A typical application circuit (figure 1) uses an operational

amplifier at the circuit input to drive the LED. The feedback

photodiode sources current to R1 connected to the inverting

The magnitude of this current is directly proportional to the

feedback transfer gain (K1) times the LED drive current

force sufficient photocurrent to keep the node voltage (Vb)

equal to Va.

The output photodiode is connected to a non-inverting

voltage follower amplifier. The photodiode load resistor, R2,

performs the current to voltage conversion. The output

amplifier voltage is the product of the output forward gain

(K2)

times

the

LED

current

and

photodiode

load,

ratio of the product of the output forward gain (K2) times the

photodiode load resistor (R2) to the product of the feedback

transfer gain (K1) times the input resistor (R1). This reduces

to

The overall transfer gain is completely independent of the

LED forward current. The IL300 transfer gain (K3) is

expressed as the ratio of the output gain (K2) to the

feedback gain (K1). This shows that the circuit gain

becomes the product of the IL300 transfer gain times the

ratio of the output to input resistors

K1-SERVO GAIN

K2-FORWARD GAIN

K3-TRANSFER GAIN

The transfer gain is the ratio of the forward gain to the servo

gain, i.e., K3 = K2/K1.

K3-TRANSFER FAIN LINEARITY

The percent deviation of the transfer gain, as a function of

LED or temperature from a specific transfer gain at a fixed

LED current and temperature.

PHOTODIODE

A silicon diode operating as a current source. The output

current is proportional to the incident optical flux supplied

by the LED emitter. The diode is operated in the photovoltaic

or photoconductive mode. In the photovoltaic mode the

diode functions as a current source in parallel with a forward

biased silicon diode.

The magnitude of the output current and voltage is

dependent upon the load resistor and the incident LED

optical flux. When operated in the photoconductive mode

the diode is connected to a bias supply which reverse

biases the silicon diode. The magnitude of the output

current is directly proportional to the LED incident optical

flux.

LED (LIGHT EMITTING DIODE)

An infrared emitter constructed of AlGaAs that emits at

890 nm operates efficiently with drive current from 500 μA to

40 mA. Best linearity can be obtained at drive currents

between 5 mA to 20 mA. Its output flux typically changes by

-0.5 %/°C over the above operational current range.

APPLICATION CIRCUIT

Fig. 1 - Typical Application Circuit

8

7

6

5

K1

1

2

3

4

K2

R1

R2

IL300

Vb

Va

+

-

U1

lp1

-

U2

+

lp2

V

out

V

CC

V

CC

V

CC

V

CC

I

F

V

C

+

R3