We found this circuit in the November 1995 Electronics Now magazine. The circuit is more accurate than the previous one using an external multimeter as an indicator.
In the figure we have the way to implement a 5 to 45 V zener diode with 50 mA of maximum current...
This circuit is from a Radio Electronics magazine from December 1958. The indicator instrument is analog...
These integrated ones consist of class B amplifiers with gain fixed 24 internally for better...