Discharge lamp lighting device

A discharge lamp lighting device comprising a series closed-loop circuit including an AC power supply, a ballast having an inductance, and a discharge lamp, and a switch circuit connected in parallel to said discharge lamp;

• in which said switch circuit comprises a full-wave rectifier connected across said discharge lamp, a main thyristor connected in series with a first impedance circuit between output terminals of said full-wave rectifier and being capable of being turned off by a gate signal, said first impedance circuit being formed by a parallel circuit connected at its one terminal in series to a cathode of said main thyristor and including a resistor and a capacitor, an auxiliary switching element connected between the gate of said main thyristor and the other terminal of said first impedance circuit, a preheating thyristor connected in parallel to said first impedance circuit, and means connected to said full-wave rectifier for firing said preheating thyristor, said main thyristor being capable of being turned on again when said preheating thyristor is turned on even when said auxiliary switching element is conducting.

A discharge lamp lighting device comprising a series closed-loop circuit including an AC power supply, a ballast choke coil and a discharge lamp, and a switch circuit connected in parallel to said discharge lamp;

• in which said switch circuit includes a full-wave rectifier connected across said discharge lamp, a first thyristor connected in series with a transistor and a first impedance circuit across the output terminals of said full-wave rectifier, said thyristor having a gate electrode and being capable of being turned off by a gate signal applied to said gate electrode, means including a semiconductor switching element connected in series with a second impedance circuit between the gate electrode of said thyristor and the output terminal of said full-wave rectifier to which said first impedance circuit is connected, the point of series connection of said semiconductor switching element and said second impedance circuit being connected to the base of said transistor.

A discharge lamp lighting device comprising a series closed-loop circuit including an AC power supply, a ballast choke coil, and a discharge lamp, and a switch circuit connected in parallel to said discharge lamp;

• in which said switch circuit includes a full-wave rectifier connected across said discharge lamp, a first thyristor connected in series with a first impedance circuit between output terminals of said full-wave rectifier and being capable of being turned off by a gate signal, said first impedance circuit having a first resistor and being connected at its one end terminal to the cathode of said first thyristor, a preheating thyristor connected between the cathode of said first thyristor and one output terminal of said full-wave rectifier where said first impedance circuit is connected and means including a semiconductor switching element connected between a gate of said first thyristor and the other end terminal of said first impedance circuit, whereby said first thyristor is turned on at the time point when the voltage applied across said discharge lamp is substantially reduced to zero and then turned off at a time point when the current flowing in said first thyristor reaches a predetermined value.

A discharge lamp lighting device comprising a series closed-loop circuit including an AC power supply, a ballast choke coil, and a discharge lamp, and a switch circuit connected in parellel to said discharge lamp;

• in which said switch circuit includes a full-wave rectifier connected across said discharge lamp, a first thyristor connected in series with a first impedance circuit between output terminals of said full-wave rectifier and being capable of being turned off by a gate signal, said first impedance circuit having a first resistor and being connected at its one end terminal to the cathode of said first thyristor, and means including a semiconductor switching element connected between a gate of said first thyristor and the other end terminal of said first impedance circuit, said semiconductor switching element comprising a second thyristor, the gate of which is connected to said first impedance circuit terminal of said first thyristor side through a second impedance circuit including a capacitor, whereby said first thyristor is turned on at the time point when the voltage applied across said discharge lamp is substantially reduced to zero and then turned off at a time point when the current flowing in said first thyristor reaches a predetermined value.