# Common emitter transistor

In a Ce transistor, why does an increase in voltage between (collector and emitter) affects voltage between (collector and base) but not Voltage between (base and emitter)?

• Where did you learn that increasing $V_{CE}$ affects $I_B$? Add context into your question (and not in the comments). Commented Sep 24, 2016 at 11:57
• Oh sorry.. I misinterpreted my book..
– Hani
Commented Sep 24, 2016 at 12:00

The collector base junction is reverse biased therefore, an increasing collector voltage has minimal change on the voltage between base and emitter.

This is because the B-E region is forward biased and exhibits a "stiff" impedance electrically. This makes it not susceptible to the extra few nano amps that arise from the increase in voltage across the reverse biased collector-base junction.

• So increasing Vce increases Collector voltage only? It doesn't decrease emitter voltage?
– Hani
Commented Sep 24, 2016 at 12:17
• Increasing the collector voltage significantly will cause a small increase in collector current and this will tend to raise the emitter voltage slightly if the emitter has an emitter resistor to ground. If the emitter is directly connected to ground then its voltage is fixed at 0V potential and cannot move. It certainly will not decrease! This change in collector current flows to the emitter and not the base (except for the small leakage mentioned in my answer). Commented Sep 24, 2016 at 12:30

simulate this circuit – Schematic created using CircuitLab Here a simplified example.

If you increase V1 then the voltage Vce will also increase. The voltage Vbe can only vary a very little bit. For now see it as stable at 0,6V. That makes Vcb = Vce - 0,6V. Therefore if Vce increases then Vcb increases as well. The increase of Vce and Ib is therefore a result of increasing V1.

• Why Vbe can vary a little bit only?
– Hani
Commented Sep 24, 2016 at 12:15
• See the junction BE as a diode in the conducting state. Due to the physical construction of the transistor the voltage over this junction can not vary much. For more explanation look in the theory of diode and transistor Commented Sep 24, 2016 at 12:32
• Oh alright!....
– Hani
Commented Sep 24, 2016 at 12:33