Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Why VBE decrease with temperature ?

Status
Not open for further replies.

MahmoudHassan

Full Member level 6
Joined
Oct 4, 2010
Messages
347
Helped
43
Reputation
88
Reaction score
39
Trophy points
1,328
Activity points
3,865
Hello again
happy weekend :)
Please help me with this question

IF VBE = VT ln (IC/IS)
how can VBE decrease with temperature eventhough VT = KT/q and it is directly related to temperature ?
IS is also dependent on temperature but I don't know if its effect is more than VT on VBE and how ?

Thanks a lot
your help is really appreciated
 

KlausST

Super Moderator
Staff member
Joined
Apr 17, 2014
Messages
20,567
Helped
4,464
Reputation
8,937
Reaction score
4,502
Trophy points
1,393
Activity points
135,931
Hi,

For a silicon bjt the temp coefficient is about -2mV/K.
It is caused by the PN junction. It is just a physical effect.

Klaus
 

FvM

Super Moderator
Staff member
Joined
Jan 22, 2008
Messages
48,961
Helped
14,345
Reputation
28,954
Reaction score
13,087
Trophy points
1,393
Location
Bochum, Germany
Activity points
282,454
Model-wise, the effect is caused by the exponential Is temperature dependency. I notice that some sources mention Vt versus temperature behaviour but don't tell anything about Is versus temperature. Look out for a profound text book!
 

crutschow

Advanced Member level 5
Joined
Feb 22, 2012
Messages
3,931
Helped
930
Reputation
1,858
Reaction score
931
Trophy points
1,393
Location
Colorado USA Zulu -7
Activity points
22,236
It's related to the energy required for the carriers to cross the PN junction. The thermal motion of the carriers reduces the amount of added energy needed, thus as the temperature increases, the forward voltage drop goes down.
 

Status
Not open for further replies.

Similar threads

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top