This 5.1 MHz circuit was found in a 1980s documentation. The frequency is given by the crystal and general purpose transistors can be used.
August 2016 - It can be obtained from Mouser Electronics the battery protectors series bq7790x of...
This circuit with a few watts of power was found in the April 1995 issue of Electronics Now...
Built-in Littelfuse itself This SiC N Channel MOSFET for 1200 V can be obtained from Mouser...