Communities

Writing
Writing
Codidact Meta
Codidact Meta
The Great Outdoors
The Great Outdoors
Photography & Video
Photography & Video
Scientific Speculation
Scientific Speculation
Cooking
Cooking
Electrical Engineering
Electrical Engineering
Judaism
Judaism
Languages & Linguistics
Languages & Linguistics
Software Development
Software Development
Mathematics
Mathematics
Christianity
Christianity
Code Golf
Code Golf
Music
Music
Physics
Physics
Linux Systems
Linux Systems
Power Users
Power Users
Tabletop RPGs
Tabletop RPGs
Community Proposals
Community Proposals
tag:snake search within a tag
answers:0 unanswered questions
user:xxxx search by author id
score:0.5 posts with 0.5+ score
"snake oil" exact phrase
votes:4 posts with 4+ votes
created:<1w created < 1 week ago
post_type:xxxx type of post
Search help
Notifications
Mark all as read See all your notifications »
Q&A

Comments on Purpose of emitter resistor in a common collector amplifier

Parent

Purpose of emitter resistor in a common collector amplifier

+3
−0

I see a lot of common collector amplifiers with the output taken across an emitter resistor.

What is the purpose of doing it this way instead of connecting your load directly to the emitter?

I should mention that I am referring to an emitter follower biased by the collector output of a previous common emitter stage.

History
Why does this post require attention from curators or moderators?
You might want to add some details to your flag.
Why should this post be closed?

0 comment threads

Post
+5
−0

First, let's nail down what circuit you are asking about. Your description is somewhat vague, so I picked this interpretation:

Image

Q2 is the emitter follower stage, driven by the previous common emitter stage of Q1. Your question seems to be why R2 exists.

Some load is needed at DC to pull the emitter of Q2 low when its base is being driven low. R2 is therefore needed whenever the load does not provide this pulldown function. There are various reasons for this. Some are:

  1. The load is capacitively coupled.
  2. The load itself is capacitive or has a substantial capacitive component. R2 and this capacitance form a time constant to bring the output low "fast enough" for whatever the application is.
  3. The circuit is designed to work with a wide range of loads.
  4. The circuit must still have a valid output signal even with no load.
History
Why does this post require attention from curators or moderators?
You might want to add some details to your flag.

1 comment thread

General comments (1 comment)
General comments
jm567‭ wrote about 4 years ago

Yup, you nailed the circuit based on my description. This clears things up alot. Thank you.