# Resistors in parallel, series or neither. H-parameters

#### KevinEamon

Joined Apr 9, 2017
284
Guys;

I'm doing derivations H parameters stuff for circuit's take this for example: -

Now according to my notes RB1 and RB2 are in parallel and that's probably true. But why?

Some common definitions for series and parallel: -

Series - All current leaving R1 enters R2.
Parallel - same voltage across both resistors.

But let's have a look at these two... Ok so we short the 5 volts for Thevenin - ok that's good.

Now both have at least 1 common voltage source - the node at the bottom of RB1 and the top of RB2.
But RB2 is grounded while RB1 is referenced to whatever the voltage is at the top of RC...

So are they in parallel truly?

#### ericgibbs

Joined Jan 29, 2010
16,747
hi Kevin,
Consider that the +5Vs and 0V are 'common' nodes with reference to the transistor Base, what does that tell you.?
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#### KevinEamon

Joined Apr 9, 2017
284
Ok bare with me here. Complex things I can understand. Sometimes I struggle with the foundations...

To answer the question. I think that's what i'm saying - if we call that N1 the node at the transistor base. Say it 2.5V... ahhh ok wait that must be that voltage there.... k I think I get it... maybe

#### ericgibbs

Joined Jan 29, 2010
16,747
hi,
You are thinking in DC, consider an AC signal.
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#### KevinEamon

Joined Apr 9, 2017
284
So it's going to fluctuate between v1 and -v1...

#### KevinEamon

Joined Apr 9, 2017
284

#### ericgibbs

Joined Jan 29, 2010
16,747
hi Kevin,
Pleased to see that you have figured it out OK.

BTW: there are lots of of Articles in the AAC files.
E

#### KevinEamon

Joined Apr 9, 2017
284
Ahhh but it's the knowing where to look. Our lectures in this, are more an exercise in math, than there are an explanation of what we're doing or why we're doing it for. But thanks v much this has cleared it up Eric.