SCR trigger circuit

Claim 2

A triggering circuit for a controlled rectifier having an anode, a cathode connected to a point of reference potential and having a gate electrode comprising, in combination: a capacitor having a first plate connected to said reference potential and having a second plate; a first switch for selectively connecting the second plate of said capacitor to said point of reference potential; a first transistor having an emitter electrode connected to the second plate of said capacitor, having a collector electrode connected to the gate electrode of said controlled rectifier, and having a base electrode; means for applying a bias potential to the base electrode of said first transistor for conditioning said first transistor to be nonconductive so long as the potential at said second plate does not depart from said reference potential by more than a predetermined value in the sense for tending to turn said first transistor on; a charging circuit connected across said capacitor for charging said capacitor in said sense for tending to turn on said transistor whenever said first switch does not connect the second plate of said capacitor to said point of reference potential, thereby to prevent the charging of said capacitor; and means for automatically clamping the gate electrode of said controlled rectifier to a potential a given time after said first transistor turns on, each time said first transistor turns on, thereby conditioning said controlled rectifier to turn off in response to reversal of the voltage at its anode electrode.

Claim 3

A triggering circuit as set forth in claim 1 wherein said means connecting the collector electrode of said first transistor to the gate electrode of said controlled rectifier includes a second capacitor for blocking protracted d-c flow, thereby to cause saturation of said first transistor after d-c flow is established by the triggering of the controlled rectifier.

Claim 4

A triggering circuit as set forth in claim 2 wherein said means for applying a bias voltage has a terminal for an operating voltage and a voltage divider connected between said terminal and said point of reference potential, said voltage divider comprising: a first resistance connected for providing a d-c conductive path between said terminal and the base electrode of said first transistor; said direct current conductive means between the base electrodes of said first and second transistors; and a second resistance connected for providing a d-c conductive path between the base electrode of said second transistor and said point of reference potential.

Claim 5

A triggering circuit as set forth in claim 1 wherein said means for automatically clamping the gate electrode of said controlled rectifier to a potential a given time after said first transistor turns on, each time said first transistor turns on, includes: means connecting the collector electrode of said first transistor to the gate electrode of said controlled rectifier for causing said first transistor to saturate after triggering said controlled rectifier and thereby to have increased base current flow; a normally open second switch connected between the gate electrode of said controlled rectifier and said point of reference potential; and means, included in said means for applying a bias potential to the base electrode of said first transistor, responsive to said increase in the base current flow of said first transistor during its saturation for closing said second switch, thereby placing the gate electrode of said controlled rectifier at a potential such that said controlled rectifier can turn off in response to reversal of the voltage at its anode electrode.

Claim 6

A triggering circuit as set forth in claim 4 wherein said second switch comprises a second transistor having a conduction path and a control electrode, said conduction path being connected between the gate electrode of said controlled rectifier and said point of reference potential, and wherein said means responsive to said increase in the base current flow of said first transistor during its saturation for closing said second switch comprises means for developing a voltage proportionally responsive to the base current flow of said first transistor and means for applying this voltage to the control electrode of said second transistor.

Claim 7

A triggering circuit as set forth in claim 4 wherein the first transistor is of one conductivity type and wherein said second switch includes a second transistor of opposite conductivity type having an emitter electrode connected to said point of reference potential, having a collector electrode connected to the gate electrode of said controlled rectifier, and having a base electrode and wherein the means responsive to said increase in the base current flow of said first transistor during its saturation for closing said second switch includes direct current conductive means between the base electrode of said first transistor and the base electrode of said second transistor, for coupling the base electrode of said first transistor to the base electrode of said second transistor.

Claim 8

A triggering circuit as set forth in claim 3 wherein said direct current conductive means between the base electrodes of said first and second transistors includes a third resistance and a further capacitor shunting at least a major portion of said third resistance.

Claim 9

A triggering circuit as set forth in claim 4 wherein said means connecting the collector electrode of said first transistor to the gate electrode of said controlled rectifier comprises differentiating means which include: a capacitor; a unilateral resistance exhibiting relatively easy conduction of current in a first direction and relatively difficult conduction in a second direction opposite to said first direction; and means connecting said capacitor, in series with said unilateral resistance between the collector electrode of said first transistor and the gate electrode of said controlled rectifier, with said unilateral resistance poled for easy conduction of the collector current of said first transistor.

Claim 10

A capacitor discharge ignition circuit comprising, in combination: a silicon controlled rectifier (SCR) having anode, cathode and gate electrodes, connected at its cathode electrode to a point of reference potential; a transformer having a primary winding; a first capacitor connected essentially in series with said primary winding across the anode-to-cathode path of said SCR; means coupled across said capacitor for supplying current pulses in a given polarity thereacross, said polarity being such as to develop a direct voltage across said capacitor in a sense to cause current flow in the forward direction through the anode-to-cathode path of said SCR; a transistor having emitter, base and collector electrodes; a second capacitor connected between said emitter electrode and said point of reference potential; means connected to said base electrode for supplying a reverse bias potential thereto; means coupling said collector electrode to the gate electrode of said SCR; a charging circuit connected across said second capacitor in a sense to produce a voltage across said second capacitor, when it charges, for causing a flow of current in the forward direction through the emitter-to-collector path of said transistor; switch means connected across said second capacitor; means for operating said switch means between closed and open conditions, said switch means, when closed, preventing said second capacitor from charging whereby said transistor remains in the off condition and, when open, permitting said capacitor to charge, whereby when the voltage across said second capacitor reaches a level sufficient to overcome the reverse bias on said base electrode, said transistor turns on and supplies a trigger pulse to the gate electrode of said SCR; and means for automatically clamping said gate electrode to substantially said reference potential a given interval of time after said transistor turns on, thereby conditioning said SCR to turn off when its anode voltage reverses upon discharge of said first capacitor through said primary winding and anode-to-cathode path.

Claim 11

A capacitor discharge ignition circuit comprising, in combination: a silicon controlled rectifier (SCR) having anode, cathode and gate electrodes, connected at its cathode electrode to a point of reference potential; a transformer having a primary winding; a first capacitor connected essentially in series with said primary winding across the anode-to-cathode path of said SCR; means coupled across said capacitor for supplying current pulses in a given polarity thereacross, said polarity being such as to develop a direct voltage across said capacitor in a sense to cause current flow in the forward direction through the anode-to-cathode path of said SCR; a transistor having emitter, base and collector electrodes; a second capacitor connected between said emitter electrode and said point of reference potential; means connected to said base electrode for supplying a reverse bias potential thereto; means coupling said collector electrode to the gate electrode of said SCR; a charging circuit connected across said second capacitor in a sense to produce a voltage across said second capacitor, when it charges, for causing a flow of current in the forward direction through the emitter-to-collector path of said transistor; switch means connected across said second capacitor; means for operating said switch means between closed and open conditions, said switch means, when closed, preventing said second capacitor from charging whereby said transistor remains in the off condition and, when open, permitting said capacitor to charge, whereby when the voltage across said second capacitor reaches a level sufficient to overcome the reverse bias on said base electrode, said transistor turns on and supplies a trigger pulse to the gate electrode of said SCR; and means for automatically clamping said gate electrode to substantially said reference potential a given interval of time after said transistor turns on, thereby conditioning said SCR to turn off when its anode voltage reverses upon discharge of said first capacitor through said primary winding and anode-to-cathode path.

Claim 12

A capacitor discharge circuit as set forth in claim 9, wherein said means for automatically clamping comprises means responsive to base current flow through said transistor.

Claim 13

A capacitor discharge circuit as set forth in claim 10, wherein said means for clamping comprises a second transistor of opposite conductivity type to the first-mentioned transistor, having a base electrode coupled to the base electrode of the first-mentioned transistor and a collector-to-emitter path connected between said gate electrode and said point of reference potential.

Claim 14

A circuit for suppressing the effect of switch bounce comprising, in combination: a first capacitor having a first plate connected to a point of reference potential and having a second plate: a switch connected across the capacitor; a transistor having emitter and base electrodes and an emitter-base junction therebetween and having a collector electrode, connected at its emitter electrode to the second plate of said first capacitor; means coupled between said base electrode and said point of reference voltage for applying a bias potential to said base electrode which conditions said transistor for non-conduction so long as its emitter potential does not depart sufficiently from said reference potential to permit forward conduction of its emitter-base junction; a second capacitor; a load circuit having a first terminal to which is connected via said second capacitor said collector electrode and having a second terminal connected to said point of reference potential; a charging circuit connected across said first capacitor for charging the same, when said switch is open, in a sense to turn on said transistor when the voltage across said first capacitor, that is, the voltage at said emitter electrode, reaches a level in excess of said bias potential by an amount sufficient to forward-bias said emitter-base junction, said switch, when closed, serving to discharge said first capacitor to thereby turn off said transistor; and means responsive to base current flow of greater than a given value through said transistor, for clamping the first terminal of said load circuit to said point of reference potential.

Claim 15

A circuit for suppressing the effect of switch bounce comprising, in combination: a first capacitor having a first plate connected to a point of reference potential and having a second plate: a switch connected across the capacitor; a transistor having emitter and base electrodes and an emitter-base junction therebetween and having a collector electrode, connected at its emitter electrode to the second plate of said first capacitor; means coupled between said base electrode and said point of reference voltage for applying a bias potential to said base electrode which conditions said transistor for non-conduction so long as its emitter potential does not depart sufficiently from said reference potential to permit forward conduction of its emitter-base junction; a second capacitor; a load circuit having a first terminal to which is connected via said second capacitor said collector electrode and having a second terminal connected to said point of reference potential; a charging circuit connected across said first capacitor for charging the same, when said switch is open, in a sense to turn on said transistor when the voltage across said first capacitor, that is, the voltage at said emitter electrode, reaches a level in excess of said bias potential by an amount sufficient to forward-bias said emitter-base junction, said switch, when closed, serving to discharge said first capacitor to thereby turn off said transistor; and means responsive to base current flow of greater than a given value through said transistor, for clamping the first terminal of said load circuit to said point of reference potential.

Claim 16

A circuit as set forth in claim 12 wherein said load circuit comprises the gate electrode-to-cathode electrode path of a silicon controlled rectifier (SCR).

Claim 17

A circuit as set forth in cliam 12 wherein said means for clamping comprises a second transistor having a base electrode and a collector-to-emitter path, said path being connected between the first terminal of said load circuit and said point of reference potential, and said base electrode of said second transistor being coupled to the base electrode of the other transistor, said second transistor being of opposite conductivity type than the other transistor.

Claim 18

A circuit as set forth in cliam 12 wherein said means for clamping comprises a second transistor having a base electrode and a collector-to-emitter path, said path being connected between the first terminal of said load circuit and said point of reference potential, and said base electrode of said second transistor being coupled to the base electrode of the other transistor, said second transistor being of opposite conductivity type than the other transistor.

Claim 19

A triggering circuit for a controlled rectifier having anode, cathode and gate electrodes, comprising: a capacitor; a transistor having emitter, base and collector electrodes, said emitter electrode being connected to one terminal of said capacitor, said collector electrode being connected to the gate electrode, said capacitor having the other terminal thereof commonly connected along with the cathode electrode to a reference potential; means for applying a bias potential at said base electrode to render said transistor non-conductive so long as the potential at said emitter electrode does not depart from said reference potential by more than a predetermined value in the sense of polarity tending to turn said transistor on; means for charging said capacitor relative to said reference potential and for discharging said capacitor to said reference potential, the potential at said emitter reaching the turn-on level of said transistor to supply a controlled rectifier turn-on signal at the gate electrode each time said capacitor is charged; and means for attenuating the signal level on the gate electrode below the turn-on level of the controlled rectifier each time said transistor reaches saturation and thereby conditioning the controlled rectifier to turn-off when the potential between its anode and cathode changes to a reversed polarity.

Claim 20

A triggering circuit for a controlled rectifier having anode, cathode and gate electrodes, comprising: a capacitor; a transistor having emitter, base and collector electrodes, said emitter electrode being connected to one terminal of said capacitor, said collector electrode being connected to the gate electrode, said capacitor having the other terminal thereof commonly connected along with the cathode electrode to a reference potential; means for applying a bias potential at said base electrode to render said transistor non-conductive so long as the potential at said emitter electrode does not depart from said reference potential by more than a predetermined value in the sense of polarity tending to turn said transistor on; means for charging said capacitor relative to said reference potential and for discharging said capacitor to said reference potential, the potential at said emitter reaching the turn-on level of said transistor to supply a controlled rectifier turn-on signal at the gate electrode each time said capacitor is charged; and means for attenuating the signal level on the gate electrode below the turn-on level of the controlled rectifier each time said transistor reaches saturation and thereby conditioning the controlled rectifier to turn-off when the potential between its anode and cathode changes to a reversed polarity.