US 5,512,810 AGranted

Variable speed control for a hand-held electric power tool

AssigneeEaton Corporation

InventorsJames E. Hansen, Jeffery L. Henderson, James R. Jaeschke

Life of this patent

Estimating the term…

Loading patent…

Abstract

A power tool has a variable speed control circuit that comprises a user switch, a motor and a thyristor connected in series between a pair of power supply terminals. A manually variable resistor is connected between a first electrode of the thyristor and a circuit node. A capacitor is coupled between the circuit node and the second thyristor electrode. A bleed-off resistor is connected between second thyristor electrode and the circuit node to provide a path for discharging the capacitor when the user switch is open. A semiconductor trigger device, such as a diac or silicon trigger switch, couples the circuit node to the thyristor gate electrode. The circuit operation ensures that the capacitor charges from substantially the same voltage level at the start of each half-cycle during which the thyristor is to be turned on.

Claims10

Dependent claims

In a hand-held power tool having an electric motor and a pair of power terminals for connection to a source of alternating electricity, a variable speed control circuit comprising:

a switch which is operable by a user of the power tool;
a triac having a gate electrode, first and second electrodes and a conduction path between the first and second electrodes with conductivity of the conduction path being controlled by voltage applied to the gate electrode, and wherein the conduction path, said switch and the motor are connected in series between the pair of power terminals;
a trigger node;
a semiconductor trigger device having a first terminal directly connected to the gate electrode of said triac and a second terminal directly connected to said trigger node;
a manually variable resistor connected between the first electrode of said triac and said trigger node;
a capacitor directly connected between the second electrode of said triac and said trigger node;
a bleed-off resistor connected between the second electrode of said triac and said trigger node to provide a path for discharging said capacitor when said switch is open;
and
a diode and a resistor connected in series between said trigger node and the second electrode of said triac to charge said capacitor at a different rate during positive half-cycles of the alternating electricity than during negative half-cycles, thereby minimizing a difference between a setting of said manually variable resistor at which the motor starts and a setting at which the motor stops.

6 more elements

In a hand-held power tool having an electric motor and a pair of power terminals for connection to a source of alternating electricity, a variable speed control circuit comprising:

a switch which is operable by a user of the power tool;
a triac having a gate electrode, first and second electrodes and a conduction path between the first and second electrodes with conductivity of the conduction path being controlled by current applied to the gate electrode, and wherein the conduction path, said switch and the motor are connected in series between the pair of power terminals;
a voltage divider connected directly across the first and second electrodes of said triac, and consisting of first and second resistors connected directly in series with a first node therebetween;
a second node;
a variable resistor operable by the user and directly connected between the first node and said second node;
a capacitor directly connected between the second electrode of said triac and said second node;
and
a bidirectional semiconductor trigger device having a first terminal directly connected to the gate electrode of said triac, and having a second terminal directly connected to said second node.

5 more elements

Dependencies are inferred from the claim text.