In the switching characteristics section of a BJT datasheet I often see test conditions like \$I_{B1}=I_{B2}=1mA\$. I understand this is the base current, but what exactly do they mean by \$I_{B1}\$ and \$I_{B2}\$?

Example: https://www.mccsemi.com/pdf/Products/MMBT3904(SOT-23).pdf


1 Answer 1


It means that the current for charging the Base is the same as the current used to discharge the Base capacitance when they do fall time testing. An exemplary circuit to do so is shown in this datasheet. enter image description here

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How to determine BJT switching time

  • \$\begingroup\$ Thank you very much. Perfect answer in no time at all. \$\endgroup\$
    – Jaywalk
    Jul 2, 2019 at 13:26
  • \$\begingroup\$ You're welcome! Please accept my answer. \$\endgroup\$
    – Daniel K
    Jul 2, 2019 at 13:38

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