Copyright: 1996 - 2024
BSEE - KB3UON
RF Cafe began life in 1996 as "RF Tools" in an AOL screen name web space totaling
2 MB. Its primary purpose was to provide me with ready access to commonly needed
formulas and reference material while performing my work as an RF system and circuit
design engineer. The World Wide Web (Internet) was largely an unknown entity at
the time and bandwidth was a scarce commodity. Dial-up modems blazed along at 14.4 kbps
while tying up your telephone line, and a nice lady's voice announced "You've Got
Mail" when a new message arrived...
All trademarks, copyrights, patents, and other rights of ownership to images
and text used on the RF Cafe website are hereby acknowledged.
My Hobby Website:
Why operating you amp near saturation gives good efficiency - RF
RF Cafe Forums closed its virtual doors in 2012 mainly due to other social media
platforms dominating public commenting venues. RF Cafe Forums began sometime around
August of 2003 and was quite well-attended for many years. By 2010, Facebook and
Twitter were overwhelmingly dominating online personal interaction, and RF Cafe
Forums activity dropped off precipitously. If the folks at
phpBB would release a version with integrated
sign-in from the major social media platforms, I would resurrect the RF Cafe Forums,
but until then it is probably not worth the effort. Regardless, there are still
lots of great posts in the archive that ware worth looking at.
Below are the old forum threads, including responses to the original posts.
|-- Amateur Radio
Gripes & Humor
-- CAE, CAD, &
Test & Measurement
Post subject: Why operating you amp near saturation gives
Unread postPosted: Wed Apr 27, 2005 3:53 am
A student recently asked me why it is claimed that operating an
amp near to saturation gives good efficiency. I suggested the following
but I would like to check the validity of my suggestions (I could be
I believe running near saturation improves efficiency
(a) The transistor's average 'on resistance' will be
less when operating near to saturation which will result in less power
dissipated in the transistor and hence higher efficiency.
With shorter transistor conduction times that come with bias nearer
to saturation the power lost in the transistor must drop as the device
is turned on for a shorter period of time per cycle.
Have I missed
anything or got it all wrong ?
Unread postPosted: Wed Apr 27, 2005 10:10 am
I think the student is not refereing to DC bias saturation but to
dynamic conditions AC output saturation.
Efficiency is the ratio
of the AC power out of the device to the DC power.
When you are
in AC saturation (Max AC current and Max AC voltage swing, for a given
load line), you just cannot get more AC juice out of the device. Necessary
in a very simple way you have maximum efficiency since you maximize
AC output for a given DC input.