Abstract: An amplifier circuit in which a first amplifier (A1) and a second amplifier (A2) are protected against short-circuits by a protection apparatus which includes a first device (M1), a second device (M2), a third device (M3) and a protection device (B). For this purpose the first device and the second device generate four signals (s1, s2, s3, s4) related to an equal number of currents (i1, i2, i3, i4), which currents are related to a first or a second load current in the first amplifier or in the second amplifier. In order to control the protection device (B), the third device generates at least two control signals (r1, r2) related to the signal currents (s1, s2, s3, s4), use being made of the equality of the load currents in the absence of short-circuits.

Abstract: An input signal (Vin) is applied to a first amplifier (A1) and a second amplifier (A2) via a circuit (M), which amplifiers are both coupled to an output terminal (U) to supply an output voltage (Vuit). For this purpose the circuit (M) generates two mutually complementary signals which are related to the output signal (Vuit) and the maximum signal values corresponding to the individual output signals of the first amplifier (A1) and the second amplifier (A2). The output signal to be supplied (Vuit) consequently dictates which amplifier (A1, A2) is driven into full conduction.

Abstract: In order to boost the output power of a first amplifier (A1) a second amplifier (A2) can increase the supply voltage difference across the first amplifier (A1). However, variations of the supply voltage difference result in comparatively high distortion. In order to minimize this distortion while maintaining the output power, a signal-follower circuit generates a direct voltage lever which tracks a first output signal of the first amplifier, for which purpose the signal-follower circuit is driven by a third amplifier, which compares the first output signal with a reference signal.