simple oscillator, where did the energy go?


Joined Dec 26, 2010
Whilst it is true that no energy conversion system is 100% efficient, there is nothing obvious about the AC output from an oscillator containing less energy than the DC input simply because of its being AC.

An oscillator based on a linear amplifier will indeed waste a good deal of energy in the simple "area under the curve" way that you may be imagining. This energy escapes as heat, principally from the transistor(s) or other active device(s) in the circuit.

On the other hand, some oscillators operate in a way more similar to switching power converters and achieve quite high efficiencies. There is still some power loss, but much less than with a linear type. This may be achieved for instance in radio-frequency oscillators which operate in "class C", where the amplifying device conducts for less than half of the cycle.


Joined Jun 6, 2011
You are also making a fabulously bad assumption that the current into your oscillator is *constant*. Assuming the output of your oscillator is driving a resistive load, the input current into your oscillator will be a sinusoid (with a DC offset).

This will cause the total power in to be considerably less than what you imagine, and far closure to the total power out than the constant current assumption.

The output stage of the oscillator will also have a great deal of impact on the overall efficiency of the power transfer characteristics. A class 'A' output will waste *lots* of power. A class 'D' output can be highly efficient (on the order of 90% or higher).

But mainly, your confusion stems from your constant input current assumption.


Joined Jan 28, 2005
As a general rule, any difference between the total input power and the total output power is lost in the form of heat.