New Reply

please help transistor amplifier

 
Share Thread Thread Tools
Nov25-12, 11:04 AM   #86
 

please help transistor amplifier


Quote by Jony130 View Post
Simply you forget about base current which loads the voltage divider in your calculations.



So to reduce this loading effect on output voltage we need increase the current that is flow through voltage divider or output current should be a small fraction of the voltage divider current.
So when we design voltage divider we assume that voltage divider current is larger then the load current.
Normally Divider current is 5 to 30 times larger then the load current.

So if we want 1.7V and load current is equal to 50μA and we choose voltage divider current 10 times larger then load current we have this

R2 = 1.7V/(10*Iload) = 1.7V/(10*50μ) = 1.5V/500μA = 3.4K

And from I Kirchhoff's Law we see that R1 resistor current is equal:

I_R1 = 10*Iload + Iload = 11*Iload = 550μA

So

R1 = (10V - 1.7V)/(550μ) = 15K

o sorry joney i make you tired, i understand now, so if load current is 50μ we chose voltage divider current 10 larger then the load current, and we have

R2 = 1.7V/(10*Iload) = 1.7V/((this is 10 time larger)10*50μ(base current)) = 1.5V/500μA = 3.4K this i understand

but this i dont understand
I_R1 = 10*Iload + Iload = 11*Iload = 550μA

10*Iload(50μA)+Iload(50μA)=11(how we get 11 now)*Iload(50μA)=550μA

i dont understand that 11 how we get? 10*Iload(50μA)+Iload(50μA)=0.55 not 11 sorry i dont know where i make mistake, where come this 11, i dont know how to calculate, i know 11*Iload is 550μA
thnx for answer
Nov25-12, 11:21 AM   #87
 
Solve this pure math problem
B = 10A + A

Also from KCL we see that R1 must provide current for R2 resistor and also the current for the load.

So if Iload = 50μA and we pick voltage divider 10 times load current we have this:

I_R1 = Iload + 10 times load current = 11 times load current = 11*50μA = 550μA
Nov25-12, 11:41 AM   #88
 
Quote by Jony130 View Post
Solve this pure math problem
B = 10A + A

Also from KCL we see that R1 must provide current for R2 resistor and also the current for the load.

So if Iload = 50μA and we pick voltage divider 10 times load current we have this:

I_R1 = Iload + 10 times load current = 11 times load current = 11*50μA = 550μA
i am with calculator in my hand, i make mistake with my calculator but i dont understand i do it 0.050+10*0.050=0.55 how to do it ? CAN YOU TELL ME PLEASE HOW TO CALCULATE WITH CALCULATOR,
Nov25-12, 11:46 AM   #89
 
Can you tell me how to calculate with calculator joney
Nov25-12, 11:48 AM   #90
 
LoL
Use Google
https://www.google.pl/search?q=0.050...-a&channel=rcs
Nov25-12, 11:55 AM   #91
 
haha i rely dont find i find one like min 0.050+10*0.050=0.55, joney were i make now mistake, with my calculator pfff i am shame

JONEY can you tell me please how to calculate in my calculator please
Nov25-12, 12:05 PM   #92
 
Joney i know you know how to do it with calculator, can you tell me because i have in my hand calculator, i can find nothing in google the same result please....
Nov25-12, 12:06 PM   #93
 
Simply use your brain instead of a calculator.
And if you still don't know how you should quit EE and start learn math.
Nov25-12, 12:13 PM   #94
 
Quote by Jony130 View Post
Simply use your brain instead of a calculator.
And if you still don't know how you should quit EE and start learn math.
JONEY i use me brain, why you dont tell me to calculate with my calculator, you just help me, i thank you for help, just tell me a little bit, and i use a calculator, you help so much, help also this one
Nov25-12, 12:15 PM   #95
 
But I don't understand what is your problem?
I_R1 = 50uA + 10*50uA = 50 + 500 = 550uA = 0.55mA = 0.00055A
Nov25-12, 12:28 PM   #96
 
Quote by Jony130 View Post
But I don't understand what is your problem?
I_R1 = 50uA + 10*50uA = 50 + 500 = 550uA = 0.55mA = 0.00055A
joney i know this from begin to calculate this is easy, but my problem was other you forget,
i ask you for this

-------------------------------
o sorry joney i make you tired, i understand now, so if load current is 50μ we chose voltage divider current 10 larger then the load current, and we have

R2 = 1.7V/(10*Iload) = 1.7V/((this is 10 time larger)10*50μ(base current)) = 1.5V/500μA = 3.4K this i understand

but this i dont understand
I_R1 = 10*Iload + Iload = 11*Iload = 550μA

10*Iload(50μA)+Iload(50μA)=11(how we get 11 now)*Iload(50μA)=550μA

i dont understand that 11 how we get? 10*Iload(50μA)+Iload(50μA)=0.55 not 11 sorry i dont know where i make mistake, where come this 11, i dont know how to calculate, i know 11*Iload is 550μA
thnx for answer
----------------------------------
joney this 11 is my problem
Nov25-12, 12:34 PM   #97
 
OMG
Look here
We have this equation
B = 10*A + A = 11*A
The first part tell as that we have a ten apples and we need add one more apple.
So we end-up with eleven apples .
Nov25-12, 12:41 PM   #98
 
Quote by Jony130 View Post
OMG
Look here
We have this equation
B = 10*A + A = 11*A
The first part tell as that we have a ten apples and we need add one more apple.
So we end-up with eleven apples .
ah you mean so
10*0.0.5+0.0.5=
10+0.5+0.5=11

you mean like this
Nov25-12, 12:56 PM   #99
 
ooh joney boy, i make again mistake of is right, ooo thank you try a lot to explain me
Nov25-12, 02:22 PM   #100
 
In our cases we have 11 apples
B = 10*A + A

And apples are equal to 50uA of load current.
So we substitute for A = 50uA
B = 10*50uA + 50uA = 550uA
And this is equal to 11*A = 11*50 = 550uA
the 11 tell as that the R1 current is 11 times large the load current.
Nov25-12, 02:27 PM   #101
 
Quote by Jony130 View Post
In our cases we have 11 apples
B = 10*A + A

And apples are equal to 50uA of load current.
So we substitute for A = 50uA
B = 10*50uA + 50uA = 550uA
And this is equal to 11*A = 11*50 = 550uA
the 11 tell as that the R1 current is 11 times large the load current.
thank you joney for losing time for me and help i go to sleep tomorow work have a nice sleep
Nov25-12, 02:31 PM   #102
 
thank you ver much joney now i start to understand
New Reply
Thread Tools


Similar Threads for: please help transistor amplifier
Thread Forum Replies
Transistor amplifier Electrical Engineering 2
Transistor AMPLifier HelP !!!! Electrical Engineering 12
Transistor AMPLifier HelP !!!! Atomic, Solid State, Comp. Physics 9
Transistor CE Amplifier Engineering, Comp Sci, & Technology Homework 2
Transistor Amplifier Introductory Physics Homework 13