US 5,294,839 A · Soft start AC tool handle trigger switch circuit

Abstract

A soft start tool handle trigger switch circuit (10) applies voltage from an AC source (12) to a portable tool electric motor (10). A current limiter (30) is connected in series between the AC source (12) and motor (14). A first sub-circuit (32) is connected in parallel with the motor (14) and includes actuator circuitry (34) tripping an actuator solenoid (36). A second sub-circuit (40) is connected in parallel with the current limiter (30) and has a pair of contacts (44, 46) actuated from an open condition to a closed condition upon movement of an actuator plunger (38). An NTC thermistor (48) is connected in series with the actuator circuitry and is physically proximate and heated by heat from the current limiter (30) to reduce the resistance of the NTC thermistor (48) and supply increased current to the actuator circuit (34) for earlier closing of the bypass sub-circuit (40), to stop the current-induced heating of the current limiter (30). Positive kick-off opening of the bypass contacts (44, 46) is provided upon release of the user finger engaged trigger (28) as the latter moves from its depressed to its extended position. Voltage sensitive (34) and time sensitive (70) circuitry is provided.

Claims11

Dependent claims

A soft start tool handle trigger switch circuit for applying voltage from an AC source to a portable tool electric motor, and having a user operated trigger movable between an on position connecting said motor to said AC source, and an off position disconnecting said motor from said Ac source, comprising:

a current limiter connected in series between said AC source and said motor;
a first sub-circuit in parallel with said motor and comprising actuator circuitry responsive to a given parameter to trip an actuator to move from a first position to a second position;
a second sub-circuit in parallel with said current limiter and in series with said motor and comprising a pair of contacts actuated from an open condition to a closed condition upon movement of said actuator from said first position to said second position,
said second sub-circuit and said current limiter being connected at a common node, said node being connected in series with said motor, and such that when said trigger is moved from said off position to said on position, AC current from said AC source is continuously supplied to said motor through said node, first through said current limiter and then through said second sub-circuit.

1 more element

a current limiting resistor connected in series between said AC source and said motor;
a first sub-circuit in parallel with said motor and comprising actuator circuitry comprising an actuator having a plunger movable between first and second positions, and an NTC thermistor in series with said actuator circuitry and heated by heat from said current limiting resistor to reduce the resistance of said NTC thermistor and supply increased current to said actuator;
a second sub-circuit in parallel with said current limiting resistor and in series with said motor and comprising a pair of contacts actuated by said actuator plunger from an open condition to a closed condition upon movement of said plunger from said first position to said second position,
said second sub-circuit and said current limiter being connected at a common node, said node being connected in series with said motor, and such that when said trigger is moved from said off position to said on position, AC current from said AC source is continuously supplied to said motor through said node, first through said current limiter and then through said second sub-circuit.

1 more element

Dependencies are inferred from the claim text.

Soft start AC tool handle trigger switch circuit

Life of this patent

Soft start AC tool handle trigger switch circuit

Life of this patent

Abstract

Claims11