This is the basic configuration of an operational amplifier sample & hold circuit. The FET and transistor are commonly used. The circuit is from an 80's documentation.
We found this configuration in an American technical documentation of 1977. The circuit can...
This simple circuit can drive a reed-relay when light falls onto the photo-transistor. The...
In the figure we have the way to obtain an adjustable constant current source of 2 mA. The...