# Difference in BJT VBE parameters

#### MikeJacobs

Joined Dec 7, 2019
223
Hello

I am trying to understand what VBE sat really is?

Also i have seen the term VBE SAT and VBE ON

What is the difference?

#### crutschow

Joined Mar 14, 2008
33,342
I am trying to understand what VBE sat really is?
It is the Vbe voltage when sufficient Ibe current is being applied to fully saturate the BJT (typically for an Ibe equal to 1/10th the Ice).
Also i have seen the term VBE SAT and VBE ON
Vbe Sat is when the transistor is saturated.
Vbe ON can be for any operating state of the transistor (such as being in the linear region).

#### MikeJacobs

Joined Dec 7, 2019
223
It is the Vbe voltage when sufficient Ibe current is being applied to fully saturate the BJT (typically for an Ibe equal to 1/10th the Ice).
Vbe Sat is when the transistor is saturated.
Vbe ON can be for any operating state of the transistor (such as being in the linear region).

Thanks

so i am not understand why IC has anything to do with VBE.
Its IB that drives how much IC can flow. So what does IC have to do with VBE?

#### crutschow

Joined Mar 14, 2008
33,342
So what does IC have to do with VBE?
Because the value of Ic can have a small effect of Vbe.

#### LvW

Joined Jun 13, 2013
1,683
Because the value of Ic can have a small effect of Vbe.
I think, the opposite is true: Ic is a function of Vbe: Shockleys famous equation: Ic=Is[exp(Vbe/Vt)-1]

"Its IB that drives how much IC can flow. So what does IC have to do with VBE? "
No - Ib and Ic are both a function of Vbe.

#### crutschow

Joined Mar 14, 2008
33,342
I think, the opposite is true: Ic is a function of Vbe: Shockleys famous equation: Ic=Is[exp(Vbe/Vt)-1]
That's ture.
But in saturation, Vbe can slightly increase with Ic due to the intrinsic base-emitter resistance.

#### BobaMosfet

Joined Jul 1, 2009
2,102
Hello

I am trying to understand what VBE sat really is?

Also i have seen the term VBE SAT and VBE ON

What is the difference?
Title: Understanding Basic Electronics, 1st Ed.
Publisher: The American Radio Relay League
ISBN: 0-87259-398-3

#### LvW

Joined Jun 13, 2013
1,683
That's ture.
But in saturation, Vbe can slightly increase with Ic due to the intrinsic base-emitter resistance.
I rather think (and I am convinced) that Shockleys equation does NOT apply in saturation mode.
And - the negative tempco (-2mV/K) tells us that Vbe must be REDUCED when Ic goes high (due to temperature increase).