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I have two optocouplers. One of them uses NPN transistor and the other one uses PNP. Each of them explicitly give the base pin of their BJTs out. Can I make a totem pole structure by connecting them as seen in the image below?

enter image description here

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2 Answers 2

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You can, but you wouldn't want to connect the bases together like that.

If you're just passing a binary signal, as implied by your LED drive circuit, just leave the bases open as usual.

If you're interested in analog signals, then you would connect the bases to a suitable bias network that establishes a quiescent operating point for the transistors.

But there's rarely a good reason to use two optoisolators when a single one followed by a suitable buffer/driver would do the job.

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  • \$\begingroup\$ I mostly agree with this, however despite the countless circuits that leave the bases open, I do not believe this is a good idea. Humidity can cause a partial conduction between base and collector causing the transistor to turn partially on. I have observed this problem when used as a gate driver causing MOSFETs to burn-out when sitting idle (supposed to be fully off). For more on this, see my first-ever stack-exchange answer: electronics.stackexchange.com/a/73066/25328 \$\endgroup\$
    – Tut
    Sep 8, 2014 at 14:15
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above ckt is possible to create the totem pole configuration,and also consider diode forward current ,the source current and sink current rating of the device as per the datasheet of the optocoupler and i will attach reference ckt enter image description here

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