# Beginner : Basic Bjt inverter ,how

Discussion in 'The Projects Forum' started by bluestone, May 11, 2008.

1. ### bluestone Thread Starter New Member

May 11, 2008
2
0
Hi to U all ,
I'm new to electronics , and in practical stuff , so our dr asked me to make simple bjt (npn) Inverter ,
This is the basic circuit
I tried to fighure out the concept that i should do , i saw lots of website , but things get mixed up .
i want to understand the main concept and the way i could detrmine the resistores RC , RB. if
the voltage vin = 5 v
vcc = 5 v
and
vin =1
Transistor Bjt , (NPN 2n2222)

2. ### mik3 Senior Member

Feb 4, 2008
4,846
63
For example, if you use Rc=1K you will 5mA to drop 5 volts across it and thus invert you input (input=high, output=low). If the lowest value of the transistors gain is 30 for example, you will need a base current of Ic/30=5mA/30=0.167mA Thus if your input voltage is 5 volts, you will need a base resistor Rb=(5-0.6)/0.167mA=26 K , 0.6 is the voltage drop across the base-emitter diode of the transistor. A better design to ensure that the transistor will always be saturated we use a base current 10 times more than the calculated so the base resistor will be 2.6 K if you like and if the maximum base current allows us to do it (check the datasheet).

3. ### hgmjr Moderator

Jan 28, 2005
9,030
214
Take a look at the material on BJT transistors in the AAC ebook at this link.

hgmjr

4. ### bluestone Thread Starter New Member

May 11, 2008
2
0
Thanks alot guys , im sorry for my late reponse though...
I tried as you mentioned , and my calculation led to Vc = 0
Thanks again.

5. ### hgmjr Moderator

Jan 28, 2005
9,030
214
If you show us your calculation I'm certain we can determine where you have gone off track.

hgmjr