Amplifier with modulated power supply voltage

In an amplifier having signal input means supplied with an input signal to be amplified, signal output means connected with a load, amplifying means connected between said signal input means and said signal output means for supplying an output signal to the latter, and power supply means for supplying an operating voltage to said amplifying means;

• a circuit for modulating said operating voltage supplied to the amplifying means in accordance with one of said input and output signals comprising direct voltage source means, a first transistor having base, emitter and collector electrodes, smoothing means connected in series with the collector-emitter circuit of said first transistor between said direct voltage source means and said amplifying means, a first resistor connected between the base and collector electrodes of said first transistor, a second transistor having base, emitter and collector electrodes, the collector-emitter circuit of said second transistor being connected between the base electrode of said first transistor and a reference voltage point, an amplitude comparator, and means for applying to said comparator a sawtooth wave signal and a signal varying with said one of the input and output signals so that said comparator provides a pulse width modulated signal having a duty factor varying with said one signal and which is applied to said base electrode of said second transistor.