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.
Hig stability is the main feature of the 10 V regulator circuit shown in the figure and suggested by...
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....
This circuit uses a 709 operational amplifier that is no longer common today. However, the same...