This circuit for 3.3 V logic circuits has a 5 V input and the maximum output current is on the order of 1 A. The circuit is from a Linear Technology manual.
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...