In this receiver the is formed by 80 turns of wire 28 or close in a ferrite rod. The handset is low impedance and powered by a standard battery.
The figure shows three circuits for using headphones in amplifiers with speakers that do not have...
In this charger, the charging current is basically limited by the LEDs. The transformer is a low...
This configuration is from an old integrated circuit manual. The circuit can be applied to modern...