Control circuit for thyristors

Claim 2

Control circuit for the trigger of a thyristor or triac by detection of the zero passage through zero of the voltage applied to its terminals, characterized in that a rectifier circuit is linked to the terminals of the thyristor and is connected to a photoelectric-emission diodE of a photocoupler which controls a first transistor by sending a signal to the trigger of the thyristor at the moment of the passage through zero of the voltage, the feed voltage of the aforementioned transistor being from the terminals of a Zener diode whose anode is linked to one of the feed conductors and the cathode of a second conductor over a resistor and a diode, a second transistor whose base is tied to the rectifier being mounted in parallel on the Zener diode.

Claim 3

Circuit according to claim 1, characterized in that the thyristor being one of the elements of a triac, the rectifier circuit consisting of a diode bridge is connected with the terminals of the triac on a diagonal, the photoelectric-emission diode of the photocoupler being connected with the terminals of the second diagonal, the phototransistor being linked to the base of the first transistor.

Claim 4

A circuit for controlling a triac, said control circuit connected to the trigger of said triac so as to send control signals to said trigger, said control circuit comprising: a zero voltage detection circuit, connected across the terminals of said triac, for detecting a zero voltage across the terminals; a photocoupler connected to said zero detection circuit, said photocoupler comprising a photoelectric-emission diode and a phototransistor for receiving light emissions from said photoelectric-emission diode, said phototransistor being operative to output a signal in response to a light emission from said photoelectric-emission diode which in turn emits light in response to a non-zero voltage condition in said zero detection circuit; and circuit means connected to said phototransistor and to said trigger and operative to transmit a signal to said trigger upon the occurrence of a lack of signal from said phototransistor.

Claim 5

A circuit for controlling a triac, said control circuit connected to the trigger of said triac so as to send control signals to said trigger, said control circuit comprising: a zero voltage detection circuit, connected across the terminals of said triac, for detecting a zero voltage across the terminals; a photocoupler connected to said zero detection circuit, said photocoupler comprising a photoelectric-emission diode and a phototransistor for receiving light emissions from said photoelectric-emission diode, said phototransistor being operative to output a signal in response to a light emission from said photoelectric-emission diode which in turn emits light in response to a non-zero voltage condition in said zero detection circuit; and circuit means connected to said phototransistor and to said trigger and operative to transmit a signal to said trigger upon the occurrence of a lack of signal from said phototransistor.

Claim 6

The control circuit of claim 3 wherein said control circuit is connected to a pair of external power terminals and said circuit means for sending a signal to said trigger comprises: a first transistor which is based connected to said phototransistor, and emitter connected to said trigger of said triac, and a feeder circuit means, connected to the emitter of said first transistor, for feeding a current to said first transistor, said feeder circuit including a switch for enabling or disabling the feeder circuit.

Claim 7

The control circuit of claim 4 wherein said zero detection circuit comprises: a diode bridge, one diagonal of which is connected across the terminals of said triac, and a second diagonal of which is connected to said photoelectric emission diode of said photocoupler.

Claim 8

The control circuit of claim 3 wherein said means for sending a signal to said trigger comprises: a first transistor connected to said trigger; means for switching said first transistor on so as to produce a single pulse to said trigger, said switching means comprising: a pair of transistors each of which is connected to said phototransistor and also connected to a thyristor so as to momentarily switch said first transistor on in response to said signal from said phototransistor.

Claim 9

A control circuit for an AC load device, comprising in combination: a thyristor having a gate electrode and a pair of main electrodes connected in series with an AC load; signal generating means connected to said gate electrode for selectively causing current conduction by said thyristor, said signal generating means including an optically responsive device which upon cessation of optical energization thereof effects current conduction by said thyristor; and light emitting means connected across said thyristor for causing cessation of optical energization of said optically responsive device upon zero crossing of voltage across said thyristor, said light emitting means comprising a series circuit of a rectifying means and a light emitting device whereby said cessation of optical energization occurs in response to non-conduction by said Thyristor during a half cycle of voltage across said thyristor followed by zero crossing of the voltage across said thyristor.

Claim 10

A control circuit for an AC load device, comprising in combination: a thyristor having a gate electrode and a pair of main electrodes connected in series with an AC load; signal generating means connected to said gate electrode for selectively causing current conduction by said thyristor, said signal generating means including an optically responsive device which upon cessation of optical energization thereof effects current conduction by said thyristor; and light emitting means connected across said thyristor for causing cessation of optical energization of said optically responsive device upon zero crossing of voltage across said thyristor, said light emitting means comprising a series circuit of a rectifying means and a light emitting device whereby said cessation of optical energization occurs in response to non-conduction by said Thyristor during a half cycle of voltage across said thyristor followed by zero crossing of the voltage across said thyristor.

Claim 11

A control circuit as defined in claim 7 wherein said series circuit also includes a switch for selectively actuating the control circuit.

Claim 12

A control circuit as defined in claim 8 wherein said signal generating means maintains said thyristor conductive continuously during half cycles subsequent to said zero crossing.

Claim 13

A control circuit as defined in claim 8 wherein said signal generating means produces pulses having a period less than that of a half cycle of voltage across said thyristor.

Claim 14

A control circuit for an AC load device, comprising in combination: a thyristor having a gate electrode and a pair of main electrodes connected in series with an AC load; signal generating means connected to said gate electrode for selectively causing current conduction by said thyristor, said signal generating means including an optically responsive device which upon cessation of optical energization thereof effects current conduction by said thyristor; and light emitting means connected across said thyristor for causing cessation of optical energization of said optically responsive device upon zero crossing of voltage across said thyristor.

Claim 15

A control circuit for an AC load device, comprising in combination: a thyristor having a gate electrode and a pair of main electrodes connected in series with an AC load; signal generating means connected to said gate electrode for selectively causing current conduction by said thyristor, said signal generating means including an optically responsive device which upon cessation of optical energization thereof effects current conduction by said thyristor; and light emitting means connected across said thyristor for causing cessation of optical energization of said optically responsive device upon zero crossing of voltage across said thyristor.

Claim 16

A control circuit as defined in claim 11 wherein said light emitting means comprises a series circuit of a light emitting diode and a switch, said switch being selectively controllable initially to produce energization of said light emitting diode during a half cycle of voltage across said thyristor followed by cessation of such energization at a following zero crossing of the voltage.