Koito Manufacturing Company, Ltd.

Masayasu Yamashita

Atsushi Toda

Goichi Oda

Jun Yabuzaki

Akihiro Matsumoto

Masaru Sasaki

Hitoshi Takeda

Hideaki Takeuchi

Toru Nakayama

Hiroki Ishibashi

Akiyoshi Ozaki

Masatoshi Sugasawa

A lighting circuit for a discharge lamp incorporates a DC-DC converter for converting DC voltage and a control circuit for controlling the output voltage from the converter by controlling the ON/OFF operation of an FET which is configured as the converter. The electric current which flows in the FET is monitored by detecting the voltage between the drain and the source to turn the field effect transistor off when the voltage level is at the reference value or higher. Thus, a pulse-by-pulse current limitation is performed. Limitation of an electric current in a switching device in a DC-DC converter of a lighting circuit for a discharge lamp is achieved while reducing the size and cost of the circuit apparatus.

Lighting circuit for discharge lamp

A discharge-lamp lighting circuit,has a DC-AC converter that incorporates a full bridge circuit consisting of a plurality of pairs of switching devices. The discharge-lamp lighting circuit incorporates an anomaly detector for detecting an anomalous state of the lighting circuit, and a current detector for detecting whether or not an electric current flows in the full bridge circuit in a state where the operation of the lighting circuit is stopped owing to detection of an anomalous state of the lighting circuit by the anomaly detector. The discharge-lamp lighting circuit also includes a device-stage determining unit structured such that when a current has been detected by the current detector, a pair of switching devices, of the switching devices connecting the full bridge circuit and disposed in the higher stage, are switched on. Another pair of the switching devices, disposed in the lower stage are switched off. The discharge-lamp lighting circuit thus prevents generation of a short circuit current owing to an anomalous state of a switching device of the plurality of pairs of switching devices.

Discharge-lamp lighting circuit

A discharge lamp lighting circuit comprising power control means for executing lighting acceleration control to supply power greater than rated power to a discharge lamp to thereby expedite lighting of the discharge lamp, and constant power control on the discharge lamp with the rated power; and timer means for regulating a time for the lighting acceleration control by the power control means in such a way that the lighting acceleration control does not continue for a predetermined time or longer, at the beginning of the lighting of the discharge lamp or when the status of the discharge lamp after being lit changes.

A discharge lamp lighting circuit which, in turning on a discharge lamp, when an abnormal condition occurs in a discharge lamp or in the present discharge lamp lighting circuit due to a transient cause, can resume the power supply to the discharge lamp at the time when the present transient abnormal condition cause disappears. The discharge lamp lighting circuit includes lighting control for controlling the lighting of a discharge lamp, an abnormal condition detector for detecting an abnormal condition occurring in the discharge lamp or in the discharge lamp lighting circuit, and a protection circuit which receives a signal from the abnormal condition detector to thereby stop the power supply to the discharge lamp. The protection circuit is composed of first protection unit and second protection unit. When a permanent abnormal condition is detected in the discharge lamp or in the discharge lamp lighting circuit, the power supply to the discharge lamp is cut off by the first protection unit and such cutoff condition of the power supply is also held. Also, when a transient abnormal condition is detected in the discharge lamp or in the discharge lamp lighting circuit, the power supply to the discharge lamp is cut off by the second protection unit and, after then, when the present abnormal condition is no longer detected, the power supply cutoff condition is removed to thereby resume the power supply to the discharge lamp. Further, while the power supply to the discharge lamp is being cut off by the second protection unit, the operation of the first protection unit is prevented from cutting off the power supply to the discharge lamp and holding such power supply cutoff condition.

Discharge lamp lighting circuit with protection circuit

A lighting circuit for a discharge lamp comprises a DC power supply circuit having a coil and a capacitor at its input stage, a DC-AC converter for converting the output voltage of the DC power supply circuit to an AC voltage and supplying the AC voltage to a discharge lamp, ignition means for generating an ignition pulse to the discharge lamp, and control means for performing variable control on the output voltage of the DC power supply circuit 3. The control means 6 performs such a boosting operation as to boost the output voltage of the DC power supply circuit 3 to a predetermined voltage under a loadless condition while the ignition pulse generated by the ignition means 5 is supplied to the discharge lamp 11 to thereby light the discharge lamp 11. During the boosting operation, the ignition means 5 applies the ignition pulse to the discharge lamp 11, lighting the discharge lamp.

A lighting circuit for a discharge lamp capable of improving the lighting performance of a discharge lamp with a simple circuit structure to thereby prevent a lighting failure at the end of the lifetime of the discharge lamp. The lighting circuit 1 comprises a DC power supply circuit 2, DC-AC conversion means 3 for converting a DC voltage output from the DC power supply circuit 2 to an AC voltage and supplying the AC voltage to the discharge lamp 5, a circuit element 6 (a switch element or a current limiting element) for blocking or limiting a current counter-flowing to the DC power supply circuit 2 from the DC-AC conversion means 3, and an inductive load 4 connected in series to the discharge lamp 5. A series circuit of a Zener diode 7 and a passive element 8 (a capacitor or a resistor) is provided in parallel to the circuit element 6, so that when the Zener diode 7 conducts, a rise in an auxiliary voltage for reignition is suppressed.

A lighting circuit for a discharge lamp which reliably detects short-circuiting of, or current leakage from, a discharge. A lighting circuit 1 has DC-AC conversion means 3 for converting a DC voltage from the DC power supply 2 to an AC voltage and supplying the AC voltage to the discharge lamp 9. The lighting circuit further comprises sampling means 4 for sampling a lamp voltage or a lamp current of the discharge lamp 9 in synchronism with a drive signal Sp sent to the DC-AC conversion means 3 to generate an AC wave, and abnormality determining means 5 for determining short-circuiting of, or current leakage from, the discharge lamp 9 based on a detection signal from the sampling means 4. When an abnormality is detected, power supply to the discharge lamp 9 is stopped.

A lighting circuit for a discharge lamp is designed in such a way that a detection time for the flicker state of a discharge lamp is not affected by the light-OFF time at the time the discharge lamp flickers without causing a significant increase in cost. This lighting circuit 1 for a discharge lamp comprises detection means 5 for detecting a flicker state of a discharge lamp 3; and abnormality determining means 6 for determining an abnormality in the discharge lamp 3 in accordance with a detection signal from the detection means 5 and implementing display to that effect, or stopping power supply to the discharge lamp 3, whereby when the detection signal from the detection means 5 indicates repetition of a state where a light-OFF time of the discharge lamp 3 is equal to or greater than a first set time and a light-ON time of the discharge lamp 3 is equal to or less than a second set time is repeated a predetermined period or longer, or a predetermined number of times or more, the abnormality determining means 6 determines the state as abnormal lighting of the discharge lamp 3.

A discharge lamp lighting device for turning on a discharge lamp, including: a power system which generates a high voltage, the power system having a grounding line; a control system having an analog circuit which has a grounding line, and a digital circuit which has a ground wire, the control system for controlling the power system; and a power source system for generating voltages to drive the power system and the control system, wherein the grounding line of the power system, the grounding line of the analog circuit in the control system and the grounding line of the digital circuit in the control system are provided independently of each other.

Discharge lamp lighting device with power system, control system and

A discharge lamp lighting circuit which, when a discharge lamp is removed from a connecting member such as a socket or the like and the discharge lamp is judged unlighted, stops the power supply to the discharge lamp to thereby prevent ill effects caused by the wrong detection of connecting condition detect means used to detect a connecting condition between the discharge lamp and connecting member. The discharge lamp lighting circuit comprises lighting control which supplies an electric power to a discharge lamp through a given connecting member (such as a socket or the like) and controls the lighting of the discharge lamp, a lighting condition detector which is used to detect the lighted or unlighted condition of the discharge lamp, a connecting condition detector which detects whether the discharge lamp is connected to the connecting member or not, and a power supply control which controls the supply of power to the discharge lamp. When the power supply control receives from the connecting condition detector a signal indicating that the discharge lamp is removed from the connecting member and also receives from the lighting condition detector a signal indicating that the discharge lamp is in the unlighted condition, the power supply to the discharge lamp is stopped.

Discharge lamp lighting circuit with lighting condition detector

A lighting circuit for a discharge lamp includes lighting control circuit for controlling the lighting of a discharge lamp, ignition means for supplying a trigger pulse to the discharge lamp and a socket. Power is supplied to the discharge lamp via terminals of the socket and terminals of a connector section of the discharge lamp. The socket and the connector section are respectively provided with connection terminals which are to be connected together while the discharge lamp is connected to the connecting member. When those connection terminals are not connected together, the supply of power and the supply of the trigger pulse to the discharge lamp are inhibited. This prevents problems (damaging insulation, an electric shock and the like) from arising when the lighting circuit is activated while the discharge lamp is not connected to the lighting circuit.

Circuit for inhibiting the supply of power to a discharge lamp

A lighting circuit for a discharge lamp has input terminals to which a DC power supply is to be connected, a DC power supply circuit for converting a DC input voltage to a predetermined voltage, and a DC-AC converter for converting the output voltage of the DC power supply circuit to an AC voltage and then supplying the AC voltage to the discharge lamp. A transformer is incorporated in the DC power supply circuit as insulator means for insulating the circuit portion at its input stage from the circuit portion at its output stage. The transformer has its high-voltage output terminal connected to a ground-side one of the input terminals to supply a negative rectangular-wave voltage to the discharge lamp.

Lighting circuit for applying a negative AC voltage to a discharge lamp

A lighting circuit for a discharge lamp comprises abnormality detection means for detecting an input voltage and/or an input current to be input to a lighting circuit from a power supply and stopping power supply to a discharge lamp when detecting an abnormality in the value of the input voltage and/or the value of the input current. First and second reference values or reference ranges for comparison (the first reference value or reference range is smaller than the second reference value or reference range) are set for the input voltage and/or the input current. When the state where the value of the input voltage and/or the value of the input current is equal to or smaller than the first reference value or the first reference range continues for a predetermined time or longer, the abnormality detection means stops power supply to the discharge lamp. When the state where the value of the input voltage and/or the value of the input current is equal to or greater than the second reference value or the second reference range continues for a predetermined time or longer, the abnormality detection means permits power supply to the discharge lamp.

Abnormality detecting circuit for discharge lamp with delayed

A lighting circuit for a discharge lamp comprises detection means for detecting a voltage and/or a current to be applied to a discharge lamp or a voltage and/or a current equivalent thereto, input voltage/current detection means for detecting an input voltage and/or an input current to the lighting circuit, and abnormality detection means for stopping power supply to the discharge lamp when detecting an abnormality in the discharge lamp or a circuit abnormality based on those detection signals. In the abnormality detection means, a plurality of reference values for comparison or a plurality of reference ranges are set for the detection signals, and determination times are set in association with the reference values or reference ranges. The abnormality detection means compares the levels of the detection signals with each of the reference values or the reference ranges and determines that an abnormality in the discharge lamp or a circuit abnormality has occurred when a certain comparison result continues for an associated determination time or longer.

Light circuit for discharge lamp

In a lighting circuit, a battery voltage is sent via a DC power supply section to a DC-AC converter to be converted to a square-wave AC voltage which is in turn supplied to a discharge lamp. The lighting circuit comprises an auxiliary power supply section for producing a predetermined voltage based on the input voltage from a battery and supplying this predetermined voltage to the individual sections of the lighting circuit and an abnormality detection circuit for detecting an abnormality in the discharge lamp, the circuit status, the battery voltage and so forth. In accordance with a signal from the abnormality detection circuit, a switch section, which is provided on a current line whose current is smaller than a current flowing on a power supply line to the discharge lamp, is switched on or off to enable or disable the auxiliary power supply section, thereby permitting or inhibiting power supply to the discharge lamp.

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Shimizu, Japan

Masayasu Yamashita