Circuit for contactless operating parameter changeover for electric tool - derives variable demand voltage from source by switching auxiliary resistance w.r.t. potential divider

摘要

The circuit defines a demand voltage (Usoll) from a stabilised supply voltage via a potential divider (6,7). The demand voltage is varied by switched variation of the potential divider ratio. The ratio is varied by switching an ohmic auxiliary resistance (10) in parallel with one of the divider resistors using a contactless switch (9) supplied by a source in series with the stabilised source. It either connects the foot point of the auxiliary resistance to that of the divider or isolates them. USE/ADVANTAGE - E.g. for electric hammer drill. Switching is achieved with low current consumption using integral circuit in electronic drive assembly.