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Image Source: https://www.vishay.com/docs/83725/4n25.pdf

The pin no 6 of the optocoupler IC is connected to the base of the NPN transistor. Should I keep it open? Or grounded? Does it anything to do with improving the performance of the optocoupler?

Sadat Rafi
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  • Maybe to bias in it so it turn on more readily? If you ground it, it will never turn on. – DKNguyen Aug 06 '20 at 20:38
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    For speedier usage or managed hysteresis. You can do a lot when you have access to the base that you cannot do, without it. – jonk Aug 06 '20 at 20:43
  • Proteus simulation shows that even if the base is grounded, the transistor turns on if the LED is turned on. – Sadat Rafi Aug 06 '20 at 20:44
  • @Justme, thanks. That question has my answer. – Sadat Rafi Aug 06 '20 at 20:47
  • @SadatRafi I don't really believe that but I've also never used one of these before. – DKNguyen Aug 06 '20 at 20:47
  • Simulations show faulty results in many cases. So, I will check it practical later. – Sadat Rafi Aug 06 '20 at 20:49
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    @SadatRafi Simulators are simulators. I think in Proteus you can also freely use microcontrollers and LCD displays without connecting power supplies properly, so people think they can omit supplies in real life too. – Justme Aug 06 '20 at 20:49

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