This is a precision half-wave rectifier, suggested by Texas Instruments. Diodes are commonly used, and resistors can have signal values. The power supply must be symmetrical.
This is a high efficiency version with the MC723 which is the Motorola version for this well-known...
This circuit was found in the March 1997 Electronics Now magazine. It uses a common analog...
This circuit is from an 80's documentation. It makes use of two SCRs with current capacity...