11/30/2004 BJT Symbols and Conventions 1/2

4/5/2018 0b075807cb551baaefc6fb4b8f4ef235.doc 1/2

BJT Symbols and Conventions

C E i i + C + E v v CB i EB i + B + B - - v v B + CE B + EC v - v - BE BC - i - i npn BJT E pnp BJT C E pnp BJT C Circuit CircuitCircuit Symbol SymbolSymbol

From KCL only we find:

iE = iB + iC

From KVL only we find:

vCE= vCB + v BE ( npn )

vEC= v EB + vBC ( pnp )

Jim Stiles The Univ. of Kansas Dept. of EECS 4/5/2018 0b075807cb551baaefc6fb4b8f4ef235.doc 2/2

Note that:

* The circuit symbols are very similar to MOSFETs, with npn like N-MOS and pnp like P-MOS.

* Positive current is defined in opposite directions for npn and for pnp (just like N-MOS and PMOS!).

* The voltages are of opposite polarity for npn and pnp.

Specifically, for npn we use vBE, vCE and vCB, whereas for pnp we use vEB, vEC and vBC. This convention typically results in positive voltage values for both npn and pnp (unlike the MOSFET convention!).

* The base current iB is not equal to zero, therefore iE iC (unlike MOSFETS)!

Jim Stiles The Univ. of Kansas Dept. of EECS