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enter image description here

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Is it possible to tell if a BJT circuit is PNP or NPN simply by looking at the circuit?

For example, for the circuits shown, how can we tell if they're PNP or NPN?

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    \$\begingroup\$ Yes. Look at the location/direction of the arrow. That is really a question for your textbook or a search engine. \$\endgroup\$
    – Eugene Sh.
    Feb 27, 2019 at 16:11
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    \$\begingroup\$ I'm voting to close this question as off-topic because there is no evidence of effort to research this answer at all. \$\endgroup\$
    – Andy aka
    Feb 27, 2019 at 16:19
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    \$\begingroup\$ A memory aid: emmiter arrow on an NPN is Not Pointing iN \$\endgroup\$ Feb 27, 2019 at 16:42
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    \$\begingroup\$ Another memory aid that has stuck with me for a while: PNP is Pointing iNward Proudly \$\endgroup\$
    – nanofarad
    Feb 27, 2019 at 17:30
  • \$\begingroup\$ Still another memory aid: PNP is Pee iN the Pot. This works really well if you rotate the symbol 90 degrees counter-clockwise thus making the collector the lid. \$\endgroup\$
    – Glen Yates
    Feb 27, 2019 at 23:04

3 Answers 3

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Quite simply, look at the arrow on the leg.

enter image description here

The arrow will always be on the emitter. Look at where the current flows. The arrow will always follow the current flow.

When the arrow is pointing away from the base, it is an NPN. When pointing towards the base, it is a PNP.

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If the arrow points towards the base it is a PNP, if it points away from the base it is an NPN.

Further, the arrow will typically be on the more positive leg for PNP and negative for NPN.

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  • \$\begingroup\$ Thank you. So would those all be PNP? \$\endgroup\$ Feb 27, 2019 at 16:13
  • \$\begingroup\$ No. Look carefully. \$\endgroup\$
    – Eugene Sh.
    Feb 27, 2019 at 16:13
  • \$\begingroup\$ All but one.... \$\endgroup\$ Feb 27, 2019 at 16:14
  • \$\begingroup\$ Oh so c) (the first one) would be NPN because the arrow above the current source is pointing away? \$\endgroup\$ Feb 27, 2019 at 16:15
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    \$\begingroup\$ Oh ok thank you. So d) since the arrow is away from the base. \$\endgroup\$ Feb 27, 2019 at 16:17
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This diagram should explain everything

enter image description here Any additional questions?

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    \$\begingroup\$ Your PNP diagram has two emitters. Ic should be labelled "collector". \$\endgroup\$ Feb 27, 2019 at 20:50
  • \$\begingroup\$ @BrianRogers Thx for spotting this silly mistake. I'll fix it. \$\endgroup\$
    – G36
    Feb 27, 2019 at 20:57

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