Dental instrument control circuit - has capacitative proximity switch on instrument connected to transistor and differential amplifier arrangement

摘要

The control circuit for dental instruments, such as scale remover, drill, etc., is operated by a switch arrangement (16) on the tool handle (22) or by foot switches. These switches are capacitative switches, which can be included in the capacitative branch of an a.c. bridge. One switch only can be in this branch, and the other branch has an adjusting capacitor (17). The diagonal branch of the bridge is connected the base connection of a transistor (4) which has its collector (19) connected to the load transistor (21) of the dental instrument by a differential amplifier (20). The capacitative switch on the instrument employs an insulated metal foil on plate forming a single pole variable capacitor operated by finger pressure, the return path being formed by the body of the user.