Welcome, Guest. Please login or register.

October 23, 2019, 02:58:46 am

Author Topic: Transistor Amplifiers...a few questions  (Read 525 times)  Share 

0 Members and 1 Guest are viewing this topic.

chid

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 213
  • Respect: +1
Transistor Amplifiers...a few questions
« on: April 30, 2008, 09:20:18 pm »
0
Hi guys,

I've read a lot about transistor amplifiers (we haven't actually covered them at school yet) but I still have a few difficulties:

Why does an increase in the base current cause a large change in the collector current? (something to do with npn junctions but I'm not sure exactly what!)

Is Vout just an AC voltage or a combination of AC and DC? (I'm getting confused with them using peak to peak sometimes... I think)

Why do they often talk about the device being 'disconnected' and then a 20 mV input signal is used?

And finally is the currrent gain similar to the voltage gain... or not?


I think I understand the quantitative side to these questions (Mao's notes are really helpful) but I feel like I don't really understand what is actually happening.


Thanks in advance.  :)



VCE 2008:
English 49                        Physics 45
Specialist Maths 47           Economics 44  
Maths Mathods CAS 50     (2007) Chemistry 46

Aggregate 208.8
ENTER 99.90

Tutoring Methods, Specialist and Chemistry in 2009!
PM me if interested.

Mao

  • CH41RMN
  • Honorary Moderator
  • Great Wonder of ATAR Notes
  • *******
  • Posts: 9188
  • Respect: +388
  • School: Kambrya College
  • School Grad Year: 2008
Re: Transistor Amplifiers...a few questions
« Reply #1 on: May 01, 2008, 08:51:28 pm »
0
i'm not exactly sure about the first question, but I do know that we dont need to know it.


for your second question, Vout can be a combination of both (usually is), unless a capacitor is placed somewhere there (there's two positions to put it) which decouples it to only AC
peak-to-peak refers to twice the amplitude of the AC component. its basically or can be written as

"disconnected" just refer to 0V from Vin, or basically just 0.7V going into Vb

and current gain is the current amplification, it depends on the transistor itself, it is . Since ICE is practically IC, and IBE is practically IB, a current gain of 100 means an Ib of will be amplified to at RC
Voltage gain depends on the circuit configuration and the current gain, where
they are kind of related.... based on similar principles, but very different things.


« Last Edit: May 03, 2008, 02:14:34 pm by Mao »
Editor for ATARNotes Chemistry study guides.

VCE 2008 | Monash BSc (Chem., Appl. Math.) 2009-2011 | UoM BScHon (Chem.) 2012 | UoM PhD (Chem.) 2013-2015

chid

  • Victorian
  • Forum Obsessive
  • ***
  • Posts: 213
  • Respect: +1
Re: Transistor Amplifiers...a few questions
« Reply #2 on: May 01, 2008, 10:44:16 pm »
0
Thanks Mao. Much appreciated.
VCE 2008:
English 49                        Physics 45
Specialist Maths 47           Economics 44  
Maths Mathods CAS 50     (2007) Chemistry 46

Aggregate 208.8
ENTER 99.90

Tutoring Methods, Specialist and Chemistry in 2009!
PM me if interested.

Collin Li

  • VCE Tutor
  • Victorian
  • ATAR Notes Legend
  • *******
  • Posts: 4966
  • Respect: +17
Re: Transistor Amplifiers...a few questions
« Reply #3 on: May 03, 2008, 01:26:51 am »
0
Why does an increase in the base current cause a large change in the collector current? (something to do with npn junctions but I'm not sure exactly what!)

You do not need to know about the operation of npn-junctions, or p-n junctions. However, to not really answer your question technically, it is helpful just to think of a base current as an input energy to open a tap. If you have more base current, you can turn the tap more, and allow more collector current to flow through. This is why a variation in the base current causes a variation in the collector current (an amplified one)