Found in American documentation from the 1990s, this circuit can generate signals of up to a few tens of megahertz. The transistor must be suitable for high frequencies.
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...