# Need Help for CE Amplifier Design

Discussion in 'The Projects Forum' started by renotenz, Oct 25, 2010.

1. ### renotenz Thread Starter New Member

Oct 25, 2010
11
0
Hello, this is my first post here. So just onto the question ,

I've got a project to design a CE Amplifier with this specifications :

The rests are unknown, only that I thought the transistor hfe is about 100 to 300.

I've got the basic idea about voltage-divider biasing and placement of coupling capacitors. The problem here is to calculate Rb1, Rb2, Rc, and Re, since I've got no idea about hie and hoe for this project (or is it not required?), so I quite confused when trying to calculate it using the small signal model.

Anyone can help? My thanks.

2. ### Audioguru New Member

Dec 20, 2007
9,411
896
hfe is the AC current gain, not the voltage gain. The hFE DC current gain is 100-300 when the collector current is 10mA. The hfe is less than the hFE.
If the collector resistor and its load are about 8 times the emitter resistor value then the voltage gain will be about 8.

The bias resistors have about 10 times the base current and their ratio is selected so that the collector voltage can swing equally in positive and negative directions.

3. ### hobbyist Distinguished Member

Aug 10, 2008
764
56

Hello,

Here are some equatins to get you started in a direction for a single stege CE biasing design.

1).Choose VCC ,(supply voltage).
2). Choose a value for IC (collector current)
3). RC = [VCC / (2*IC) ]
4). RE = RC / Av.
5). VE = IC * RE
6). VB = VE + Vbe
7). RB1 (base to ground resistor) = 10 to 20 times RE
8). ID = VB / RB1
9). RB2 (base to positive supply) = [ (VCC - VB) / ID ]

Note:

Depending on parameters you are given to work in, there are many other ways to approach this same problem.

These equations should work somewhat satisfactory in designing within the parameters you were given the task to design in.

It is up to you to add to it or deviate from it (the equations) to get the best design you can achieve.