How to use Opto Coupler

[eng_shady00]

optocoupler tutorial

I'm designing an ECG cuircuit.
I need to use Opto Coupler to isolate the human body from the electronic circuit and the power supply.
I've got 4N35 opto-coupler. I've the datasheet but still don't know how to connect the 4N35.
Anyone can help...?
Thanks alot.

 

[LordAli]

how to use optocoupler

Hi,
look at Texas instrument's : Getting the most out of your instrumentation amplifier design. Maybe it's number SLYT226. It's from analog application journal 2005, 4Q. There's example how to design ECG. You will use optoisolation after DAC and also you use SMPS for galvanic isolation.

 

[kender]

optocouplers tutorial

It depends on the overall design of your ECG/EKG. Tell us more about it.

There are at least 3 different places for galvanic isolation. If your device is completely battery powered and doesn't have any wired connections (e.g. USB, RS232), you can get away without galvanic isolation at all.

- Nick

 

[eng_shady00]

pc123 optocoupler datasheet

Thanks for your great responces...

I intended to use the opto isolator at the input of my PCB directly after the connection of patient..

My PCB use an ordinary 12 V AC/DC adaptor, so there's a danger for patient from the 50 hz interference.
I thought that the best way to protect and isolate patient is to use opto coupler.
What's your idea about that.

Any block diagram for an ECG circuit has an input block called (Protection or Isolation), i thought i could protect patient by that way.

Sometimes i found circuits with diodes connected back to back, but i think this can't represent a good isolation.
Is that right ??

 

[LordAli]

how to use opto

Still you have to preprocess input signal with amp before driving it into an optocoupler. It means, you have to isolate power supply for powering an amp. And also you have to deal with optocoupler non-linearity (in analog circuit)

By my opinion, it's better to isolate at 2 places (in digital circuit and power supply) instead of isolating every input.

Moreover, if you look at the 12V adapter, you will surely notice, that it's very cheap smps with very basic surge voltage protection (sometimes even without it).

 

[kender]

opto coupler used in ecg

By my opinion, it's better to isolate at 2 places (in digital circuit and power supply) instead of isolating every input.

Well, ECG/EKG may have as little as one input (after the InAmp). Then something like Claire LOC110 could be used as a linear optocoupler.
Another potential approach is to keep the microcontroller on the isolated side and optocouple power and serial output (if there is one).

 

[hakeen]

optocoupler usage

If you want to tighten linearity of signals from sensors, use a high linearity coupler, something like HCNR200.

 

[liusupeng]

opto input example

simply speaking, input current to the opto coupler is proportioanl to the output current.

 

[kender]

ekg optocoupler circuit

simply speaking, input current to the opto coupler is proportioanl to the output current.

That's an oversimplification. Generally speaking, optocouplers are grossly nonlinear.

 

[akss_here]

instrument 24v optocoupler output

tutorial link...

http://www.cisl.columbia.edu/kinget_group/student_projects/ECG Report/E6001 ECG final report.htm#0

 

[qolpa]

best opto coupler circuit

hi,
i am designing a smps whic is capable of giving 24V,10A.
i have a question. when i use TLP421 as a opto in my circuit current limit is 9A and if i just changed the opto(all the other hardware is same) to PC123 current limit increases to 9,6A. output voltage doesnt change.

they have 2 main differences from the datasheet. Vce and forward voltages. any idea?

regards