Hi there,
sorry for this question..maybe can be silly for many of you..but I'm freaking out trying to understand how this circuit works..
the idea is to use it for bias scaling..with screen scaling
here is the circuit..and then will follow the question ;)
I tried to simulate the circuit with PSPICE and to change Resistor values in order to understand how it works..
Vout follows Vin with a coefficient related to Vscr...
I think that the two transistor works in their linear region of operation...
Suppose that I want to get Vout in the range 90V to 10V (the 90 volts is obtained when Vscr is 400V and the 10V when Vscr is 200V)
So now I have to calculate the resistors value in order to obtain this result!
I think that R4 and R5 are used to make NPN transistor works in linear region but I don't know how to calculate them ..
The same applies to R1 R2 and R3...
How is the formula I have to use to calculate them (I think their relations.. i.e. R1 is half of R2 and R3 is double than R2)..
I actually don't know how to start
I found that if R1 is very small related to R2 and R3 the Vout lowers (I mean MAX VOUT goes toward zero volt while if R1 is 2 or 3 times smaller than R2 I can get 100V on Vout when Vscr is 400 and Vin is 100V)
Is there anyone that can help me to calculate the proper values for R1 to R5 in order to obtain , let me say a value Vout (in a specified range) when I have fixed Vin and the range of Vscr?
Thanks a lot in advance and sorry for my english
Krusty
sorry for this question..maybe can be silly for many of you..but I'm freaking out trying to understand how this circuit works..
the idea is to use it for bias scaling..with screen scaling
here is the circuit..and then will follow the question ;)
Code:
NPN
Vin _____________ _C__ __ E_ ______________ Vout
 \___/ 
 B 
R4  
______ R3
 
R5 
 PNP 
__C_ __E_ 
\___/ 
B R2
 
 __________________Vscr
GND 
R1

GND
Vscr = from 200V to 400 V
Vin = 100V
Vout = ??
Vout follows Vin with a coefficient related to Vscr...
I think that the two transistor works in their linear region of operation...
Suppose that I want to get Vout in the range 90V to 10V (the 90 volts is obtained when Vscr is 400V and the 10V when Vscr is 200V)
So now I have to calculate the resistors value in order to obtain this result!
I think that R4 and R5 are used to make NPN transistor works in linear region but I don't know how to calculate them ..
The same applies to R1 R2 and R3...
How is the formula I have to use to calculate them (I think their relations.. i.e. R1 is half of R2 and R3 is double than R2)..
I actually don't know how to start
I found that if R1 is very small related to R2 and R3 the Vout lowers (I mean MAX VOUT goes toward zero volt while if R1 is 2 or 3 times smaller than R2 I can get 100V on Vout when Vscr is 400 and Vin is 100V)
Is there anyone that can help me to calculate the proper values for R1 to R5 in order to obtain , let me say a value Vout (in a specified range) when I have fixed Vin and the range of Vscr?
Thanks a lot in advance and sorry for my english
Krusty