This polarity inverter circuit for voltages down to about -12 V was found in the December 1992 issue of Radio Electronics magazine. The current is a few mA.
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...