In the figure we have an interesting protection bridge against power polarity inversion of a circuit using power MOSFETs. MOSFETs must have currents according to the protected load.
The circuit shown is from the Texas Instruments optoelectronics manual, applying to low power...
This circuit was found in a 1968 General Electric documentation. It has an input impedance of 2 M ohms...
This filter that rejects a frequency range determined by the double-T was found in the August 1993...