This circuit for cars with fans was found in Silicon Chips documentation from the 90s. It is used to activate the fan when the radiator water temperature rises.
This circuit has both frequency and duty cycle control. We found it in the October 1992 Radio...
This power supply is indicated for the supply of not very powerful car radios of the AM and FM...
In the absence of a modulation signal, the carrier of this simple short-range transmitter is cut...