what is the output of basic class C? - diyAudio
Go Back   Home > Forums > General Interest > Everything Else

Everything Else Anything related to audio / video / electronics etc) BUT remember- we have many new forums where your thread may now fit! .... Parts, Equipment & Tools, Construction Tips, Software Tools......

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 14th November 2011, 01:20 PM   #1
diyAudio Member
 
Join Date: Jan 2010
Default what is the output of basic class C?

Hi,
As i refer to all the results i search from the web, i found that usually books introduce class c amplifier output waveform is as shown in figure 1. But some others will show the output waveform like figure 2. Anyone can help me to solve this doubt?

Figure 1
Untitled.jpg

Figure 2
Electronic_Amplifier_Class_C.png

thank you
  Reply With Quote
Old 14th November 2011, 01:59 PM   #2
expert in tautology
diyAudio Member
 
bear's Avatar
 
Join Date: Apr 2002
Location: New York State USA
Class C is not for audio. It is for RF. In the case of class C the output circuit "fills in" the missing space in the waveform, in effect an integrator... not a low distortion thing either, but effective for making things like an RF carrier...

_-_-bear
__________________
_-_-bear
http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ]
  Reply With Quote
Old 14th November 2011, 02:01 PM   #3
diyAudio Member
 
Join Date: Jan 2010
so should i see a small positive cycle pulse or a negative cycle pulse in the collector?
  Reply With Quote
Old 14th November 2011, 02:33 PM   #4
diyAudio Member
 
Join Date: Jun 2011
OK the first picture is an idealized representation, the second is true in the case of the common emitter amplifier shown, because the common emitter is an inverting amplifier.

Normally the collector resistor in the diagram would be replaced by an LC 'tank' circuit and the transistor would operate with a narrow conduction angle (<180 degrees).

The output (close to a sine wave) would be taken from the tank circuit either from a tap on the coil, by making the inductor a transformer, or by a split capacitor 'transformer' to provide a match to the next section, usually a filter.

Last edited by counter culture; 14th November 2011 at 02:37 PM.
  Reply With Quote
Old 14th November 2011, 03:51 PM   #5
DF96 is online now DF96  England
diyAudio Member
 
Join Date: May 2007
Fig 1 says it is current. Fig 2 is presumably voltage, so they are both showing different aspects of the same thing.
  Reply With Quote
Old 14th November 2011, 04:15 PM   #6
diyAudio Member
 
Join Date: Jun 2011
Quote:
Originally Posted by DF96 View Post
Fig 1 says it is current. Fig 2 is presumably voltage, so they are both showing different aspects of the same thing.
Of course, silly me, it's widely known that a positive current flows when a negative voltage is applied.
  Reply With Quote
Old 14th November 2011, 07:56 PM   #7
Elvee is offline Elvee  Belgium
diyAudio Member
 
Elvee's Avatar
 
Join Date: Sep 2006
Class C simply means the amplifying element is active <180° of the cycle. In audio, this supposes it happens twice / cycle, since there is no tuned circuit to reconstruct the missing half-cycle.

Class C can have uses in audio, when combined with something else: see Broskie's class A-C f.e.
__________________
. .Circlophone your life !!!! . .
♫♪ My little cheap Circlophone© ♫♪
  Reply With Quote
Old 15th November 2011, 01:30 AM   #8
diyAudio Member
 
Join Date: Jan 2010
But isnt it ac voltage and current flow in the same phase when pass through resistor?which is as shown in figure below?sorry if i'm asking a stupid question.
untitled.JPG
  Reply With Quote
Old 15th November 2011, 02:37 AM   #9
diyAudio Member
 
Join Date: Jun 2011
Quote:
Originally Posted by Elvee View Post
In audio, this supposes it happens twice / cycle
No. This would result in frequency doubling. Class C can be used in audio where the requirement for fidelity is very low, such as in a loudhailer.

Quote:
Originally Posted by motbuddy View Post
But isnt it ac voltage and current flow in the same phase when pass through resistor?which is as shown in figure below?sorry if i'm asking a stupid question.
Attachment 249457
Yes. DF96 is wrong, his reply is misleading. My second answer was sarcastic (a joke), I apologise for that. In the (class C) common emitter amplifier the transistor conducts when the voltage on the base is sufficiently positive. Current flows into the collector and the voltage at that point drops.

Last edited by counter culture; 15th November 2011 at 02:53 AM.
  Reply With Quote
Old 15th November 2011, 03:07 AM   #10
Enzo is offline Enzo  United States
diyAudio Member
 
Join Date: Sep 2004
Location: Lansing, Michigan
That simple single-transistor stage in fig 2 will invert the polarity of the signal. Regardless of class, the basic common emitter stage will always invert the polarity of the signal. Feed the output of the first stage through another similar stage and the circuit again inverts the waveform polarity, so two stages in sequence results in the original signal polarity. That is why in discussions of signal "phase" through an amp, yo hear mention of even number of stages versus odd number of stages.

The more positive the base is made, the more the transistor conducts. The more it conducts, the higher the current through the load resistor. And Ohm's Law tells us the more curent through the resistor, the more voltage across the resistor. The top end of that resistor is hopefully conected to the powr supply, so the voltage at that end stays the same. SO then increasing the voltage across the resistor must mean the bottom end of it - the collector of the transistor - will wind up at a lower voltage.

Forget polarity for a moment. Unless polarity was your only question. Look at fig 1. With a continuous sine wave into the class C amp, the resulting output is just those peaks. Now look at fig 2. With the continuous sine wave into the transistor, the output is just the peaks as well. Yes, they are now at opposite polarity, but the waveform is still only those peaks. The way it is drawn, those peaks are narrower looking than in fig 1, but the difference is the same as turning the horizontal sweep speed control on your scope. It only appears different.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Basic class D amp questions loheswaran Class D 11 10th May 2011 09:53 PM
basic bridge rectifier question.. ac on output wicked1 Power Supplies 6 9th September 2009 11:36 PM
A basic chipamp in a not so basic case. waltson Chip Amps 19 24th August 2005 07:40 AM
Basic Preamplifier (Balanced Output) thinker10 Tubes / Valves 3 11th November 2003 04:06 PM


New To Site? Need Help?

All times are GMT. The time now is 09:34 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright ©1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2