Excitation control circuit for electromagnet coil

Claim 2

A circuit for controlling the energization of an electromagnetically operated device, said device including a stationary magnet, an armature and a coil positioned to induce magnet flux in the magnet and the armature for causing the armature to move from a first position where the armature is spaced from the magnet to a second position where the armature engages the magnet when the coil is energized by direct current, said circuit comprising: a pair of rectifying bridge networks each having a pair of input terminals and a pair of output terminals, circuit meAns connecting the input terminals of the pair of networks to an alternating current source for causing a direct current potential between the output terminals of a first of said pair of networks to have a magnitude greater than a direct current potential between the output terminals of a second of the networks when said networks are energized by the source, a transistor having an emitter and a collector connected in series with the coil in a circuit connected between the output terminals of both networks and the emitter and a base connected between the output terminals of both networks in a direction to cause the transistor to conduct and cause the coil to be energized by an output current from the first network when both of said networks are energized and to conduct and cause the coil to be energized by an output current from the second network when the second network is energized and the first network is de-energized, and switching means in the circuit connecting the input terminals of the first network to the alternating current source for causing the first network to be de-energized when the armature is at the second position.

Claim 3

A circuit for controlling the energization of an electromagnetically operated device, said device including a stationary magnet, an armature and a coil positioned to induce magnet flux in the magnet and the armature for causing the armature to move from a first position where the armature is spaced from the magnet to a second position where the armature engages the magnet when the coil is energized by direct current, said circuit comprising: a first rectifying bridge network having a positive polarity output terminal, a negative polarity output terminal and a pair of input terminals, circuit means connecting the input terminals to an alternating current source for energizing the network and causing a direct current potential between the positive and negative terminals, a transistor having a pair of main electrodes and a base electrode, circuit means connecting the main electrodes and the coil in series with the positive and negative terminals and connecting the base to one of the output terminals for causing the transistor to conduct and the coil to be energized with a current flow having a magnitude sufficient to maintain the engagement between the armature and the magnet when the first network is energized, a second rectifying bridge network having a positive polarity output terminal, a negative polarity output terminal and a pair of input terminals, means including a circuit connecting the input terminals of the second network to an alternating current source for energizing the second network and causing a direct current potential to be present between the output terminals of the second network that has a magnitude greater than the potential between output terminals of the first network, circuit means connecting the main electrodes and the coil in series with the positive and negative terminals of the second network and connecting the base to one of the output terminals of the second network for causing the transistor to conduct and the coil to be energized with current flow from the second network having a magnitude sufficient to cause the armature to move from the first position to the second position and for blocking current flow through the base of the transistor from the first network when the first and the second networks are energized, and switching means connected in the circuit between the source and the input terminals of the second rectifier for causing the second network to be de-energized when the armature is at the second position.

Claim 4

A circuit for controlling the energization of an electromagnetically operated device, said device including a stationary magnet, an armature and a coil positioned to induce magnet flux in the magnet and the armature for causing the armature to move from a first position where the armature is spaced from the magnet to a second position where the armature engages the magnet when the coil is energized by direct current, said circuit comprising: a first rectifying bridge network having a positive polarity output terminal, a negative polarity output terminal and a pair of input terminals, circuit means connecting the input terminals to an alternating current source for energizing the network and causing a direct current potential between the positive and negative terminals, a transistor having a pair of main electrodes and a base electrode, circuit means connecting the main electrodes and the coil in series with the positive and negative terminals and connecting the base to one of the output terminals for causing the transistor to conduct and the coil to be energized with a current flow having a magnitude sufficient to maintain the engagement between the armature and the magnet when the first network is energized, a second rectifying bridge network having a positive polarity output terminal, a negative polarity output terminal and a pair of input terminals, means including a circuit connecting the input terminals of the second network to an alternating current source for energizing the second network and causing a direct current potential to be present between the output terminals of the second network that has a magnitude greater than the potential between output terminals of the first network, circuit means connecting the main electrodes and the coil in series with the positive and negative terminals of the second network and connecting the base to one of the output terminals of the second network for causing the transistor to conduct and the coil to be energized with current flow from the second network having a magnitude sufficient to cause the armature to move from the first position to the second position and for blocking current flow through the base of the transistor from the first network when the first and the second networks are energized, and switching means connected in the circuit between the source and the input terminals of the second rectifier for causing the second network to be de-energized when the armature is at the second position.

Claim 5

The circuit as recited in claim 1 including a diode connected in the circuit between like polarity output terminals of both networks for preventing current flow from the output terminals of the first network through the second network whereby the rectifying components of the second network may have a lower voltage rating than the rectifying components of the first network.

Claim 6

The circuit as reciTed in claim 1 including a Zener diode having a first side connected to the series circuit at a junction between the coil and the transistor and a second side connected through a circuit to the base of the transistor for limiting the voltage across the transistor to a predetermined value when both of the networks are de-energized and the transistor is biased toward conduction by a voltage caused by inductive energy in the device.

Claim 7

The circuit as recited in claim 1 including a Zener diode connected between the base and the emitter of the transistor and a resistor connected in the emitter circuit of the transistor to limit conduction of the transistor to a predetermined value.

Claim 8

The circuit as recited in claim 1 wherein the switching means in the circuit connecting the input terminals of the first network to the alternating current source includes a triac and a circuit for switching the triac to a conductive state, said switch circuit comprising a capacitor connected in a circuit between a gate and a main electrode of the triac and a charging circuit for the capacitor including a rectifying diode and normally closed switching contacts that are moved to a circuit opening position when the armature is at the second position.

Claim 9

The circuit as recited in claim 6 wherein the circuit connecting the capacitor to the gate and main electrode of the triac includes a Zener diode connected to prevent current flow in the circuit when the charge on the capacitor is less than a predetermined value.

Claim 10

The circuit as recited in claim 6 including a second triac having main electrodes connected between one of the input terminals of the first network and one side of the source and one main electrode and a gate electrode connected to a circuit including a main electrode of the first mentioned triac.

Claim 11

The circuit as recited in claim 1 wherein the alternating current source for the first network includes a first transformer having a secondary winding having a pair of output terminals connected to the pair of input terminals of the first network respectively and the alternating current source for the second network includes a transformer having a primary winding connected to be energized by the output of the secondary winding of the first transformer.

Claim 12

The circuit as recited in claim 1 including a diode connected in the circuit between like polarity output terminals of both networks for preventing current flow from the output terminals of the first network through the second network whereby the rectifying components of the second network may have a lower voltage rating than the rectifying components of the first network, a Zener diode having a first side connected to the series circuit at a junction between the coil and the transistor and a second side connected through a circuit to the base of the transistor for limiting the voltage drop across the transistor to a predetermined value when both of the networks are de-energized and the transistor is conducting current caused by inductive energy in the device.