I am using 6N137 opto-isolator for my circuit.

enter image description here

I have attached schematic for the same. I am giving Input and Enable from SMPS as shown and ground is same. VCC and EN is 3.3V from SMPS.

But while checking output voltage when Input and EN is High ( VCC is also High ie 3.3V ), I am getting Logic High at output (3.3V).

Ground for both is same.

Link for datasheet : http://www.vishay.com/docs/84732/6n137.pdf

Can anyone help me for above issue.

Thanks in advance.

  • 1
    \$\begingroup\$ Minimum recommended Vcc is 4.5V and you are using 3.3V. What is the measured voltage between pins 2 and 3? \$\endgroup\$ Apr 19, 2015 at 11:58
  • \$\begingroup\$ pin 2 voltage was 5 v and pin 3 was 0V. \$\endgroup\$ Apr 19, 2015 at 12:16
  • \$\begingroup\$ Also, either connect your 0.01 uF cap from pin 5 to pin 8, or get rid of it altogether. If you elect to keep it, increase it to 0.1 uF per the data sheet. And make sure it's a ceramic. \$\endgroup\$ Apr 19, 2015 at 21:26

2 Answers 2


You should hew to the datasheet recommended minimum voltage of 4.5VDC if you want reliable operation, however it does not appear that is the proximate issue.

Your measurement of +5V at 2 and 0V at 3 indicates you have a wiring problem or you've damaged the LED (perhaps by accidentally connecting it without a resistor for even an instant). The LED forward voltage should be around 1.3-1.6V- and that is a good indication that it is actually emitting light. If it is much less or much more, that indicates a short somewhere (perhaps internally) or an open (again, perhaps internally). In your case it appears to be open.

As an aside, your 200 ohm resistor is a bit on the low side- I suggest keeping the nominal current more like 10mA. That is not what damaged the LED (if that's the problem) just better for long-term reliability.


According to datasheet, minimum supply voltage VCC is 4.5V. Change the voltage if you can and test it again.


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