low-frequency amplifier for radio receivers, particularly for car radios

摘要

The circuit changes the voltage level of the audio stage, typically by a factor of two, when the power demand exceeds a set threshold, and switches back to the lower value when the demand falls below the given limit. The advantage of the voltage change is that at high power demands the max. power output limit of the amplifier is raised when required whilst the steady state losses remain at a low value. The voltage changing circuit (15) may contain a voltage doubler (18) and a complementary switching transistor pair (19) under the control of a level detector (20). The latter is responsive to the output of the audio amplifier (10, 11). The amplifier power supply (16, 17, U3) is then switched in response to load demands.