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.
Published in 1988 in Hands On Electronics, this circuit converts the 12 V of a battery into 120 V AC...
The current accross the LED as function of the resistor value is given by the formulas. The...
This circuit was found in an old 1980s valve documentation. The circuit can directly replace a...