# Reverse Saturation Current of BJT

This may be a weird question but for a BJT, we have

$$\I_S\$$ is the reverse saturation current and $$\I_C\$$ is the collector current which flows through all three parts of the BJT.

Now my question is, $$\I_S\$$ should also flow through all three parts of the BJT, so can't we just add/subtract $$\I_S\$$ from $$\I_C\$$ via KCL? Is that where the -1 comes from?.

• -1 is there to make the Ic zero when Vbe is zero. – atmnt Jan 16 at 22:56
• $I_S$ is a property of the transistor, not a physical current that actually flows through it. The $I_S$ in that equation is close to the reverse saturation current of the base-emitter junction, but the equation is off by a factor of $\beta$. – TimWescott Jan 16 at 23:26
• I discuss it here and here. – jonk Jan 17 at 3:06