This constant current charger from 1997 Linear Technology Applications uses common components at the time. The transformer is the critical component, being designed according to the load voltage.
In the figure we have a classic Clapp oscillator configuration for a frequency of a few tens of...
This circuit takes advantage of the inductance of the phone in the resonant circuit. The circuit is...
In the figure we have the way to increase the voltage of a 78xx by adding a zener diode. The...