This circuit is from an American 80's documentation. The circuit indicates when the voltage of a 9 V battery drops below 7 V. The transistors can be BC548.
The Buck-type DC-DC converter (voltage lowerer) shown in figure 11 is suggested by Analog Devices...
This circuit, which appears in other versions on this website, was obtained in old documentation. The load...
This circuit is from an Electronic Design from the 90's. The main integrated circuit is uncommon...