# Common emitter amplifier - A/C source and DC source in parallel question

#### mohit+electronics

Joined Jun 11, 2020
1
I read somewhere that DC and AC should not be connected in parallel.
Question #1
In below common emitter circuit is Vin parallel to Vcc?
Question #2
Assuming C1 is not there (blocker for DC circuit),
Vcc = 5V
R1 = R2 = 10K
Voltage divider value at R1 and R2 is 2.5V
What should be Vin range assuming peak voltage of 1V:
a) 2.5V +- 1V ( 1.5V - 2.5V - 3.V)
b) 0 +- 1V (-1V - 0V - 1V)
I am trying to understand if A/C voltage source has to match voltage divider voltage which is 2.5V in our example.

#### MrChips

Joined Oct 2, 2009
22,537
I read somewhere that DC and AC should not be connected in parallel.
Question #1
In below common emitter circuit is Vin parallel to Vcc?
Question #2
Assuming C1 is not there (blocker for DC circuit),
#0. Perhaps the statement is taken out of context.
#1. No. Vin is in parallel with VB. (after series C1)
#2. Makes no sense. You must leave C1 in place. The purpose of C1 is so that Vin does not interfere with VB DC bias.

#### crutschow

Joined Mar 14, 2008
26,044
You need to look up the definition of "parallel" as pertains to circuits.