I'm interested in calculating iterative values for resistors.
For example, an emitter resistor's value may be based on the
emitter voltage divided by some current I need to have.
However, the emitter voltage is, of course, dependent on the
emitter/collector current which will depend on the emitter
resistor value. An iterative process could track down this
value closely, but I don't know how to write the expression.
Here's an example of what I mean:
Vcc
|
,------x
| |
\ |
/ R2 |
\ |
| |
| |/e Q2
x----| PNP
| |\c
| |
| '-----> to the load
|/c Q1
>-----| NPN
control |\e
signal |
at Vdd |
or 0V, \
not at / R1
Vcc \
|
|
gnd
In this case, R1 needs to be:
R1 = (Vdd - Vbe(Q1))/(I(load)/10+Vbe(Q2)/R2+Ib(Q1))
I want to set up I(load) to some value and have R1 computed from
that.
When I type V(N001,N003) as part of the expression, in order to
get the Vbe(Q1) for example, it's rejected with "Unable to find
definition of model v - default assumed." This isn't what I
want, naturally.
Is there any way to set up the expression for R1, appropriately?
Jon
