Discharge lamp lighting circuit
AssigneeKoito Manufacturing Co., Ltd.
InventorsTomoyuki Ichikawa, Kotaro Matsui, Yusuke Kasaba
Life of this patent
Estimating the term…
Abstract
A discharge lamp lighting circuit includes a power supplying portion having a half bridge inverter for converting an output of a DC power supply into AC power, and a bridge driver for driving the half bridge inverter, and a control portion for generating a control signal S1 to control a driving frequency F of the bridge driver. The control portion has a random number generating circuit for generating a random number signal and changes the driving frequency F in accordance with the random number signal at a time interval of N/F, wherein N is an integer of one or more.
Claims7
A discharge lamp lighting circuit for supplying, to a discharge lamp, an AC power to light the discharge lamp, the discharge lamp lighting circuit comprising:
- a power supplying portion having an inverter circuit for converting an output of a DC power supply into the AC power and having a driving circuit for driving the inverter circuit;
- and
- a control portion for generating a control signal to control a driving frequency F of the driving circuit,
- the control portion having a random number generating circuit for generating a random number signal and for changing the driving frequency F in accordance with the random number signal at a time interval of N/F, wherein N is an integer of one or more.
A lighting device for a vehicle, comprising;
- a discharge lamp lighting circuit for supplying, to a discharge lamp, an AC power to light the discharge lamp,
- the discharge lamp lighting circuit comprising:
- a power supplying portion having an inverter circuit for converting an output of a DC power supply into the AC power and having a driving circuit for driving the inverter circuit;
- and
- a control portion for generating a control signal to control a driving frequency F of the driving circuit,
- the control portion having a random number generating circuit for generating a random number signal and for changing the driving frequency F in accordance with the random number signal at a time interval of N/F, wherein N is an integer of one or more,
- wherein the control portion is configured to generate the random number signal to have a periodicity in a cycle which is longer than the time interval of a change in the driving frequency F and is longer than an inverse number of an acoustic resonance frequency of the discharge lamp,
- wherein the random number generating circuit includes a shift register and an exclusive OR gate and is arranged to generate, as the random number signal, an M sequence having a periodicity determined by the number of digits of the shift register, and
- wherein the control portion is configured to change the driving frequency F in accordance with the random number signal in a predetermined time zone at a start of a lighting operation of the discharge lamp.
Dependencies are inferred from the claim text.