Why operating you amp near saturation gives good efficiency - RF Cafe Forums

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Steve R
Post subject: Why operating you amp near saturation gives good efficiency
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 wrong).

I believe running near saturation improves efficiency becuase:-

(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.

(b) 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 ?

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Guest
Post subject:
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.

Posted 11/12/2012