EPC111_17 Datasheet, PDF (9/14 Pages) Espros Photonics corp – Fully integrated standalone light barrier driver & receiver

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 is a current source capable to drive typically 1mA and has an inverted output signal. 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. T3, R4 and R5 inverse the signal. The current source
for the output LED is built by the darlington circuit T1 / T2 and R2 and R3. 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 ground of the epc111 or to the cathode of the photo diode. This driver circuit operates
with a VDDLED in a range of 10 to 30 VDC.
C2 1μF
C3 100nF
+3.3V
C4 100nF
C5 4.7nF
PD
epc300
VDD
epc111
VDD33
VDD18
PD
LED
OUTN
OUTH
GND
VDD = +24V
LED
R6
R10
10k
10k
R8
12k
R7
T3
3k6
T4
BC856
BC846
R4
10k
IR LED
TSML1000
T1
BC846
T2
BCP56
R9
4k7
R5
1k
R2
1k
R3
1R2
R1
100R
C1
47μF
Low ESR
GND
OUTN
OUTH
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, ...
© 2013 ESPROS Photonics Corporation
9
Characteristics subject to change without notice
Datasheet epc111_112 - V2.5
www.espros.ch