Continue to Site

Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Pc817 opto coupler input protection

Status
Not open for further replies.
R

raman00084

Full Member level 6
Joined
Nov 29, 2010
Messages
362
Helped
2
Reputation
4
Reaction score
2
Trophy points
1,298
Activity points
4,006
the attached schematic works fine in harsh industrial noise environment, without any fault. my doubt is the capacitor(c1) 100 nf across the led will cause any damage kindly help? without the capacitor c1 the opto-coupler led some times lights lightly due to sudden motor switching are any other noise creating device is on.
 

Attachments

  • PC817.jpg
    PC817.jpg
    46.4 KB · Views: 780

There is nothing that could be damaged by the addition of this capacitor. An appropriate note is that as a general rule for industrial applications it is always important to add decoupling capacitors from 24v to GND near to sensitive components.
 
Hi,

the problem of the circuit (without capacitor) is:

Any (accidental) DC current flow causes the same current through the optocooupler diode. And you will see this current at the output.

***
A resistor instead of the capacitor generates a threshold of about 0.3mA (depending on optocoupler).
Then a dc current of less than those 0.3mA will cause no optocoupler current.

The capacitor is a good solution for noisy environment.
The resistor is good at leakage current (DC).

Maybe a combination of both is the best solution.

Klaus
 
https://obrazki.elektroda.pl/5136371900_1479753691.jpg
attached schematic.
now i changed the circuit a little. this works extremely fine in harsh industrial conduction. my doubt is weather the capacitor c1 10nf across emiter and collector of 817 opto is safe are it will damage the 817 transistor kindly advise.
 

This one is worse; when opto get switched On, the whole charge of capacitor will flow through the transistor without any resistor to limit the surge current.
 

the value of the capacitor is 10nf only
 

i replace opto to led and checked
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Back
Top