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epc134/epc135/epc136/epc137/epc138/epc139

Application Information

Light Barrier Application

The following circuit is recommended to operate the epc134/135/136/137/138/139 as a photo diode amplifier in a single beam light barrier:

D2

C1

R1

epc13x

PD

CN

OUT

VN

VSS

VDD

Type

T1

R2

GND LED

from digital

oscillator or

μC output

+VLED

D1

C2

C3

digital output

to logic, PLC

or μC

Light path

Recommended Components Values

R1: 27k(epc135/137/138), 6.8k(epc134) and 4.7k (epc136/139) (bias resistor). Sensitivity can be reduced by the reduction of this resistor.

R2: dependent on the required LED current

C1: Usually not needed. May be up to 100 pF (refer to section 'Photodiode Capacitance').

C2: 33nF (DC input current filter capacitor)

C3: 100nF or greater (power supply filter capacitor)

D1: PIN photo diode, epc200 or epc3xx family or similar devices

D2: IR LED, TSML1000 (Vishay) or similar devices

Working Principle

The IR LED D2 emits light pulses which are sent towards the photo diode D1. If there is no obstacle between the two devices, the light pulse

Design Precautions

The sensitivity at pin PD is very high in order to achieve a long operation range of light barriers even without lenses in front of the IR LED

and/or the photo diode. Thus, the pin PD is very sensitive to EMI. Special care should be taken to keep the PCB track

at pin PD as short as possible (a few mm only!). This track should be kept away from the IR LED signal tracks and

from other sources which may induce unwanted signals. It is strongly recommended to cover the chip, the photodiode

and all passive components around the chip with a metal shield. A recommended part is shown in the following figure:

The pins at the bottom are to solder the shield to the PCB with electrical connection to VDD. The hole in the front is

the opening window for the photo diode. The back side of the PCB below the sensitive area (D1, C1, R1, epc13x)

shall be a polygon connected to VDD to shield the circuit from the back side. C1 must be of high mechanical stability

(no piezoelectric effect) in order to avoid unwanted signals by mechanical shock or vibration.

Ambient Light

Photodiode DC current can be generated by ambient light, e.g. sun light. DC currents at pin PD do not generate an output signal. However, if

Photodiode Capacitance

If the photodiode capacitance is below the specified value, the system becomes more sensitive to power supply ripple voltage at higher fre-

quencies (>200kHz). This sensitivity can be reduced by a parallel capacitor to the photodiode. However, this measure reduces the detection

sensitivity. If the photo diode capacity is above the specified value, a lower detection sensitivity and a higher sensitivity spread results.

© 2014 ESPROS Photonics Corporation

Characteristics subject to change without notice

8

Datasheet_epc134-139_digital-V2.5

www.espros.ch

ecommended EMC

shield