This circuit was found in a 303 Circuits issue of Elektor magazine from the 1990s. The circuit uses an equivalent operating system. The source is not symmetrical.
In figures 1 and 2 we have two current drains that can be made with operational amplifiers and...
Great sensitivity for the circuit can be obtained with a Darlington amplification step for the...
The used diode is an unusual component today. We found this 12 V regulator in documentation from the...