This low power circuit was obtained from an American 80's documentation. The circuit indicates the voltage of a battery being trimmed by the trigger point. The transistors can be the BC549.
The circuit in the figure is suggested by ST Microelectronics (www.st.com) and consists of a...
The transistors of this circuit may be the BC548 or BC549 and its power supply can be performed...
This circuit is from Mullard's transistor reference manual from 1960. The circuit will also work...