Value used as the reference value to determine the transistor is in sat or active

[spark360z]

What is the value used as the reference value to determine the transistor is in sat or active?

Before we enforce Vce to be 0.2V. There's reference volt value. On different book they said the different value

ex. (Vce<1V, Vce<0.7V, Vce<0.2V )--->transistor is in saturation mode and we enforce Vce to be 0.2V.

Where do these numbers come from and why they said the different value which one is the actual number?

Thank you

Sorry for my English

 

[Pjdd]

There is no exact Vce value that can be called a standard or reference saturation voltage. It differs from transistor to transistor. Even for the same transistor, it will vary with the collector current level and with temperature.

For example, one particular type may have a Vce(sat) of 0.2V at a collector current of 50mA and 0.35V at 100mA. Another transistor may have a Vce(sat) of 0.1V at 50mA and 0.15V at 100mA.

It also varies slightly with the amount of Ib being forced into the base, which is why Vce(sat) is always specified in datasheets for a given Ic/Ib ratio. The specified ratio is usually 10 but may be 20 for high-beta transistors, and lower than 10 for low-beta power transistors.

 

[erikl]

As the cross-over between saturation and active region is continuous, there can't exist a single fixed reference value, moreover the value depends on the applied collector current, s. e.g. these Ic vs. Vbe characteristics of an npn BJT.

Various definitions could be used for a Vce(sat) reference value:

• a certain δIc/δVce value
• any Vce value in the middle between the steeply rising saturation curve and the more or less horizontal characteristic in the active region
• the cross-over between the (prolongation of the) steeply rising curves in the saturation region and the (horizontal) used Ic value

I prefer the last definition, which (nearly) correlates with a constant Rce .