Method and driving circuit for HID lamp electronic ballast
AssigneeMatsushita Electric Works R&D Laboratory, Inc.
InventorYiyoung Sun
Life of this patent
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Abstract
A circuit arrangement and method thereof for operating high intensity discharge (HID) lamps with a lower frequency rectangular current waveform, in which the frequency of the higher frequency ripple superimposed on the lower frequency rectangular current is modulated by a pseudo-random noise signal. The pseudo-random noise may be generated by a feedback shift register. The feedback shift register may incorporate run length interrupt logic to address PWM frequency stagnation by reducing the longest run length or lengths of the feedback shift register. The feedback shift register may also or alternatively include an RC low pass analog filter to address PWM frequency stagnation. The center frequency and frequency band of the pseudo-randomly generated noise may be adjustable.
Claims24
A method of driving a high intensity discharge lamp, comprising:
- delivering power to the high intensity discharge lamp during normal operation after starting using a lower frequency rectangular wave current;
- modulating a frequency of a higher frequency ripple using a pseudo-random signal, said pseudo-random modulation preventing arc instability due to acoustic resonance;
- and
- superimposing the pseudo-randomly modulated higher frequency ripple on the lower frequency rectangular wave current delivered to the high intensity discharge lamp.
A discharge lamp driving circuit for driving a high intensity discharge lamp, said circuit comprising:
- DC voltage input connections for powering the discharge lamp driving circuit;
- lamp-driving connections between which the high intensity discharge lamp is connectable;
- bridge circuitry connected to the DC voltage input connections, said bridge circuit including high/low frequency driver control circuitry connected to drive switching elements of the bridge circuitry, said high/low frequency driver control circuitry igniting the lamp connected between said lamp driving connections by a higher frequency voltage, biased by a lower frequency rectangular voltage during starting;
- an LC tank circuit connected to the lamp driving connections and to the switching elements of the bridge circuitry;
- a voltage controlled pulse width modulation (PWM) ramp generator connected to the high/low frequency driver control circuitry to modulate the switching duty cycle of the switching elements using a PWM signal;
- and
- a digital pseudo-random noise generator connected to the voltage controlled PWM ramp generator to modulate the frequency of the PWM signal by pseudo-random noise.
Dependencies are inferred from the claim text.