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.