The circuit is from the 1994 National Semiconductor Linear Applications Handbook but can be implemented with more modern operational amplifiers. The power supply must be symmetrical.
This circuit is from a Popular Electronics of the 90's. Any power MOSFET can be used. The circuit...
This circuit is from an Italian magazine Radio Elettronica of January 1977. The circuit shows how...
This polarity test or indicator indicates the polarity of a power line by LEDs. The circuit is...