Switching circuit for motor start winding

Claim 2

In an AC motor without a start capacitor and having a main winding and a start winding each connectable with an AC source of applied voltage, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate signal at a gate terminal; start winding circuit means for connecting said start winding and said power terminals in series across said AC source to cause the phase of start current through the thyristor means and the start winding to lag the phase of the applied voltage, the phase lag increasing with motor speed; resistive means; capacitive means; first control means for connecting said resistive means and said capacitive means across said AC source, the connection including a junction; and second control means connecting said junction to said gate terminal for developing said gate signal at a predetermined firing angle with respect to the phase of the applied voltage, said predetermined firing angle approximately coinciding with the phase lag of said start current when said AC motor reaches a desired start winding cut-out speed.

Claim 3

The switching circuit of claim 1 wherein said second control means includes voltage breakdown means in series between said junction and said gate terminal, said voltage breakdown means having a breakdown potential substantially less than the magnitude of voltage from said AC source to cause a charge voltage across said capacitor means to trigger said voltage breakdown means at least once for each cycle of AC voltage.

Claim 4

The switching circuit of claim 2 wherein said second control means further includes resistive means in series with said voltage breakdown means.

Claim 5

The switching circuit of claim 2 including third control means comprising a second resistive means and a second capacitive means in series across said AC source, said third control means including a junction between the second resistive and second capacitive means, the time constant of said third control means being different than the time constant of said first control means, and said second control means includes additional means connected with the junction in said third control means to pass to said thyristor means a pair of spaced triggering pulses generated by said first and third control means.

Claim 6

The switchIng circuit of claim 4 wherein said addittional means comprises a second voltage breakdown means connected in series between the junction of said third control means and said gate terminal.

Claim 7

The siwtching circuit of claim 1 in which said thyristor means has four quadrants of operation defined by four different combinations of positive and negative voltages at said power terminals and said gate terminals, said second control means includes safety means for enabling said thyristor means only for two of said four quadrants of operation.

Claim 8

The switching circuit of claim 6 wherein said safety means includes additional thyristor means, impedance means connected in series across said first named thyristor means, and means connecting said additional thyristor means to said impedance means to trigger the additional thyristor means in said two quadrants of operation.

Claim 9

In a capacitor start AC motor having a main winding and a start winding each connectable with an AC source of applied voltage, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate signal at a gate terminal; a start capacitor; start winding circuit means for connecting said start winding, said power terminals and said start capacitor in series across said AC source to cause the phase of start current to lead the applied voltage; resistive means; capacitive means; first control means for connecting said resistive means and said capacitive means across said AC source, the connection including a junction; and second control means connecting said junction to said gate terminal through relaxation oscillator means for triggering said thyristor means in response to the relative phase difference between the phase of said start winding current and the phase of said voltage from said AC source.

Claim 10

In a capacitor start AC motor having a main winding and a start winding each connectable with an AC source of applied voltage, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; thyristor means having power terminals exhibiting conductive and nonconductive states therebetween under control of a gate signal at a gate terminal; a start capacitor; start winding circuit means for connecting said start winding, said power terminals and said start capacitor in series across said AC source to cause the phase of start current to lead the applied voltage; resistive means; capacitive means; first control means for connecting said resistive means and said capacitive means across said AC source, the connection including a junction; and second control means connecting said junction to said gate terminal through relaxation oscillator means for triggering said thyristor means in response to the relative phase difference between the phase of said start winding current and the phase of said voltage from said AC source.

Claim 11

The switching circuit of claim 8 wherein said relaxation oscillator means includes impedance means connected to a junction between said start capacitor and said start winding, voltage breakdown means connected between said impedance means and said gate terminal, and shunt thyristor means connected between said first control means and said series connected impedance means and voltage breakdown means for controlling the energization of said relaxation oscillator means.

Claim 12

In an AC motor having a main winding and a start winding each connectable with an AC source of alternating voltage having positive and negative portions, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; a bidirectional thyristor device having a pair of power terminals for passing both positive and negative portions of alternating voltage when triggered into a conductive state under control of a gate signal at a gate terminal, said bidirectional thyristor device being triggered into said conductive state for any of four combinations of positive and negative signals at said gate terminals and said power terminal, said four combinations defining four quadrants of operation each having a different gate signal sensitivity; start winding circuit means for connecting said start winding and said pair of power terminals in series across said AC source to gate both positive and negative portions of alternating voltage to said start winding through said bidirectional thyristor device; and control means for generating a plurality of gate signals for each cycle of alternating voltage when said AC motor is below a cut-out speed, one of said plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a positive portion of said alternating voltage and another of said Plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a negative portion of said alternating voltage, including gate means for blocking gate signals occurring during two of said four quadrants, thereby preventing said bidirectional thyristor device from being triggered into conduction during either of said two quadrants.

Claim 13

In an AC motor having a main winding and a start winding each connectable with an AC source of alternating voltage having positive and negative portions, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; a bidirectional thyristor device having a pair of power terminals for passing both positive and negative portions of alternating voltage when triggered into a conductive state under control of a gate signal at a gate terminal, said bidirectional thyristor device being triggered into said conductive state for any of four combinations of positive and negative signals at said gate terminals and said power terminal, said four combinations defining four quadrants of operation each having a different gate signal sensitivity; start winding circuit means for connecting said start winding and said pair of power terminals in series across said AC source to gate both positive and negative portions of alternating voltage to said start winding through said bidirectional thyristor device; and control means for generating a plurality of gate signals for each cycle of alternating voltage when said AC motor is below a cut-out speed, one of said plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a positive portion of said alternating voltage and another of said Plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a negative portion of said alternating voltage, including gate means for blocking gate signals occurring during two of said four quadrants, thereby preventing said bidirectional thyristor device from being triggered into conduction during either of said two quadrants.

Claim 14

The switching circuit of claim 10 wherein said gate means comprises controllable conduction means, said control means includes electrical path means in parallel with said AC source for developing two trigger signals for each cycle, each trigger signal having a phase fixed with respect to the phase of alternating voltage, and network means connecting said electrical path means to said controllable conduction means to control the state of said controllable conduction means in response to said two trigger signals.

Claim 15

The switching circuit of claim 11 wherein said electrical path means comprises resistive means and capacitive means connected in series across said AC source, the junction between said resistance means and capacitance means being coupled to a voltage breakdown device connected to said network means.

Claim 16

In an AC motor having a main winding and start winding each connectable with an AC source of alternating voltage having positive and negative portions, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; a bidirectional thyristor device having a pair of power terminals for passing both positive and negative portions of alternating voltage when triggered into a conductive state under control of a gate signal at a gate terminal, said bidirectional thyristor device being triggered into said conductive state for any of four combinations of positive and negative signals at said gate terminal and said power terminal, said four combinations defining four quadrants of operation each having a different gate signal sensitivity; start winding circuit means for connecting said start winding and said pair of power terminals in series across said AC source to gate both positive and negative portions of alternating voltage to said start winding through said bidirectional thyristor device; and control means for generating a plurality of gate signals for each cycle of alternating voltage when said AC motor is below a cut-out speed, one of said plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a positive portion of said alternating voltage and another of said plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a negative portion of said alternating voltage, including safety means for causing said one gate signal and said another gate signal to effectively produce identical operation of said bidirectional thyristor device for two quadrants of said four quadrants of operation, said safety means comprises first trigger means responsive to only one of said positive and negative portions for generating a first gate signal which triggers said bidirectional thyristor device into conduction to pass said one portion, and second trigger means responsive to prior generation of the first gate signal for generating a second gate signal which triggers said bidirectional thyristor device into conduction to pass the remaining of said positive and negative portions of alternating voltage.

Claim 17

In an AC motor having a main winding and start winding each connectable with an AC source of alternating voltage having positive and negative portions, a switching circuit for controlling the application of power to the start winding, comprising: main winding circuit means for connecting said main winding in parallel with said AC source; a bidirectional thyristor device having a pair of power terminals for passing both positive and negative portions of alternating voltage when triggered into a conductive state under control of a gate signal at a gate terminal, said bidirectional thyristor device being triggered into said conductive state for any of four combinations of positive and negative signals at said gate terminal and said power terminal, said four combinations defining four quadrants of operation each having a different gate signal sensitivity; start winding circuit means for connecting said start winding and said pair of power terminals in series across said AC source to gate both positive and negative portions of alternating voltage to said start winding through said bidirectional thyristor device; and control means for generating a plurality of gate signals for each cycle of alternating voltage when said AC motor is below a cut-out speed, one of said plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a positive portion of said alternating voltage and another of said plurality of gate signals being capable of triggering said bidirectional thyristor device to pass a negative portion of said alternating voltage, including safety means for causing said one gate signal and said another gate signal to effectively produce identical operation of said bidirectional thyristor device for two quadrants of said four quadrants of operation, said safety means comprises first trigger means responsive to only one of said positive and negative portions for generating a first gate signal which triggers said bidirectional thyristor device into conduction to pass said one portion, and second trigger means responsive to prior generation of the first gate signal for generating a second gate signal which triggers said bidirectional thyristor device into conduction to pass the remaining of said positive and negative portions of alternating voltage.

Claim 18

The switching circuit of claim 13 wherein said second trigger means is responsive to a voltage which appears in said start winding circuit means when said bidirectional thyristor means changes from a conductive to a nonconductive state to generate said second gate signal, whereby the change from a conductive to a nonconductive state indicates the prior generation of the first gate signal.

Claim 19

The switching circuit of claim 14 wherein said second trigger means is coupleD to a junction between the start winding and said power terminals of said bidirectional thyristor device, whereby said voltage corresponds to the sum of the alternating voltage from said AC source and a voltage induced in said start winding.

Claim 20

The switching circuit of claim 14 wherein said first trigger means comprises electrical path means connected in parallel with said AC source, said electrical path means including phase shift means for causing said first gate signal to lag the phase of alternating voltage from said AC source.

Claim 21

The switching circuit of claim 16 wherein said electrical path means includes capacitive means, and diode means for charging said capacitive means with only one of said positive and negative portions of alternating voltage, and said phase shift means includes a voltage breakdown device coupled to said capacitive means for generating said first gate signal when the voltage across said capacitive means exceeds the breakdown potential of said voltage breakdown device.