This circuit activates a relay when the supply voltage drops below the value set in the trimpot. The transistors can be the BC548 and BC558 and the 6 V relay. The circuit was found in a 1999 Poptronics.
The components used in this National Semiconductor circuit are not common today, but the...
This 2001 circuit is used with transceivers to increase the gain of a microphone and thus obtain...
In the figure we have the configuration of a variable voltage regulator with two transistors and a...