epc111/112

Applications

Long range light barrier application

Figure 10 shows the epc111 as an example in a long range light barrier application with minimal part count. The LED flashes according to the

description of the previous chapter. Light of the LED is passing either direct, reflected from a reflecting object or a retro reflector to the photo

diode PD. If the received light fulfills the criteria according to the description in the previous chapter, the output signals OUTN and OUTH are

set.

The epc111 device is designed to operate at 3.3V power supply (VDD and VDD33).

LED Driver:

The output LED of the epc111 to drive the LED driver circuit is a current source capable to drive typically 1mA. For a high performance long

range light barrier (>8m), an LED peak current of up to 1.5A is needed. To generate such a high LED current, an external driver circuit is

necessary. The circuitry in Figure 10 is a simple implementation of such a driver circuit. The darlington circuit with T2 and T3 and R2 and R3

does the job. In order to avoid interference on the supply voltage, the supply is isolated (filtered) with R1 and C1. The high peak LED pulse

current is delivered by the capacitor C1, which itself is charged by R1. Make sure, that there is no coupling of the high LED current to the

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11.01.2011

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OUTH

LED

OUTN

PD

VDD33

VDD

epc111

GND

VDD18

R3

1R2

C1

47μF

Low ESR

GND

+3.3V

VDD

LED

= +24V

OUTH

OUTN

PD

epc300

T2

BC846

R2

1k

R5

3k6

R4

10k

IR LED

TSML1000

R1

100R

C3 100nF

C2 1μF

C5 4.7nF

C4 100nF

R6

12k

R8

10k

R7

4k7

T1

BC846

T3

BCP56

Marked conductors must be short and low ohmic

C2

The epc111 device with its very sensitive input PD needs a well decoupled power supply

Figure 10: Long range light barrier application with minimal part count

Notice:

The schematic is for illustrating the basic circuit idea only. For the real built up the designer has to take all other additional influence factors in

consideration too e.g. design rules, power rating, heat dissipation, ...

© 2011 ESPROS Photonics Corporation

Characteristics subject to change without notice

9

Datasheet epc111_112 - V2.2

www.espros.ch