These circuits were found in Exar documentation from the 90s. The circuits use both a small speaker and a piezoelectric transducer. The integrated circuit is not common today.
This power amplifier configuration can be used in a public address system (ads) in the car. The...
This circuit was found in Philips documentation from 1967. The phototransistor is from that time,...
The oscillator shown in the figure can generate signals between 3 and 15 MHz approximately, depending...