Fluorescent lamp power supply

Claim 2

A power supply for a fluorescent lamp comprising: generating means for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising pulse width modulation means, operating at a lower frequency than said high frequency, for periodically interrupting the supply of said high frequency energy to provide bursts of said high frequency energy at said lower frequency rate; and control means for controlling said switching means to control the brightness of said fluorescent lamp by controlling the duration of said bursts of said high frequency energy.

Claim 3

The supply of claim 1 wherein said control means comprises a controllable DC voltage coupled to said pulse width modulation means for changing the duty cycle of said pulse width modulation means.

Claim 4

The supply of claim 2 wherein said generating means comprise a parallel resonant self-oscillating converter, said pulse width modulating means disabling said generating means at said lower frequency rate for time periods determined by said duty cycle.

Claim 5

A power supply for a fluorescent lamp comprising: generating means comprising a parallel resonant selfoscillating converter for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising pulse width modulation means, operating at a lower frequency than said high frequency, for periodically interrupting the supply of said high frequency energy to provide bursts of said high frequency energy at said lower frequency rate; and control means comprising a controllable DC voltage coupled to said pulse width modulation means for changing the duty cycle of said pulse width modulation means to control the brightness of said fluorescent lamp by controlling the duration of said bursts of said high frequency energy, said pulse width modulating means disabling said generating means at said lower frequency rate for time periods determined by said duty cycle, said pulse width modulation means comprising two comparators and charge/discharge circuit means for operating one of said comparators as an oscillator.

Claim 6

A power supply for a fluorescent lamp comprising: generating means comprising a parallel resonant selfoscillating converter for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising pulse width modulation means, operating at a lower frequency than said high frequency, for periodically interrupting the supply of said high frequency energy to provide bursts of said high frequency energy at said lower frequency rate; and control means comprising a controllable DC voltage coupled to said pulse width modulation means for changing the duty cycle of said pulse width modulation means to control the brightness of said fluorescent lamp by controlling the duration of said bursts of said high frequency energy, said pulse width modulating means disabling said generating means at said lower frequency rate for time periods determined by said duty cycle, said pulse width modulation means comprising two comparators and charge/discharge circuit means for operating one of said comparators as an oscillator.

Claim 7

The supply of claim 4 wherein said generating means includes a pair of transistors each including a base drive resistor; said pulse width modulation means further including a gate transistor coupled to said base drive resistors for disabling base drive to said transistors as a function of the duty cycle of said pulse width modulation means.

Claim 8

A power supply for a fluorescent lamp comprising: a source of DC voltage subject to change in voltage; DC to AC converter means coupled to said source of DC voltage for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising a pulse width modulator, operating at a lower frequency than said high frequency, coupled to said converter means for interrupting said converter means at a rate equal to said lower frequency to supply bursts of said high frequency energy to said fluorescent lamp; reference potential means coupled to said DC voltage source for developing a reference potential that is substantially independent of variations in the voltage of said DC voltage source; and control means coupled to said reference potential means for controlling the duty cycle of said pulse width modulator to compensate for changes in brightness of said fluorescent lamp, due to changes in voltage of said voltage source, by varying the duration of said bursts of said high frequency energy.

Claim 9

A power supply for a fluorescent lamp comprising: a source of DC voltage subject to change in voltage; DC to AC converter means coupled to said source of DC voltage for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising a pulse width modulator, operating at a lower frequency than said high frequency, coupled to said converter means for interrupting said converter means at a rate equal to said lower frequency to supply bursts of said high frequency energy to said fluorescent lamp; reference potential means coupled to said DC voltage source for developing a reference potential that is substantially independent of variations in the voltage of said DC voltage source; and control means coupled to said reference potential means for controlling the duty cycle of said pulse width modulator to compensate for changes in brightness of said fluorescent lamp, due to changes in voltage of said voltage source, by varying the duration of said bursts of said high frequency energy.

Claim 10

A power supply for a fluorescent lamp comprising: a source of DC voltage subject to change in voltage; DC to AC converter means coupled to said source of DC voltage for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising a pulse width modulator, operating at a lower frequency than said high frequency, coupled to said converter means for interrupting said converter means at a rate equal to said lower frequency to supply bursts of said high frequency energy to said fluorescent lamp; reference potential means coupled to said DC voltage independent of variations in the voltage of said DC voltage source; and control means coupled to said reference potential means for controlling the duty cycle of said pulse width modulator to compensate for changes in brightness of said fluorescent lamp, due to changes in voltage of said voltage source, by varying the duration of said bursts of said high frequency energy; and said pulse width modulator comprising: a pair of comparators; charge/discharge means in circuit with one of said comparators and forming an oscillator; means supplying the output of said oscillator to the other of said comparators; and said control means being coupled to said other comparator and the output of said other comparator being coupled to said converter means.

Claim 11

A power supply for a fluorescent lamp comprising: a source of DC voltage subject to change in voltage; DC to AC converter means coupled to said source of DC voltage for developing a high frequency voltage for supplying high frequency energy to a fluorescent lamp; switching means, comprising a pulse width modulator, operating at a lower frequency than said high frequency, coupled to said converter means for interrupting said converter means at a rate equal to said lower frequency to supply bursts of said high frequency energy to said fluorescent lamp; reference potential means coupled to said DC voltage independent of variations in the voltage of said DC voltage source; and control means coupled to said reference potential means for controlling the duty cycle of said pulse width modulator to compensate for changes in brightness of said fluorescent lamp, due to changes in voltage of said voltage source, by varying the duration of said bursts of said high frequency energy; and said pulse width modulator comprising: a pair of comparators; charge/discharge means in circuit with one of said comparators and forming an oscillator; means supplying the output of said oscillator to the other of said comparators; and said control means being coupled to said other comparator and the output of said other comparator being coupled to said converter means.

Claim 12

A self-regulating power supply for a fluorescent lamp comprising: a parallel resonant self-oscillating converter for developing a high frequency, high voltage output for supplying a fluorescent lamp with high frequency energy from a DC voltage source that is subject to variation in voltage; low frequency pulse width modulation means coupled to said DC voltage source; means for developing a reference potential coupled to said DC voltage source; comparator means in said low frequency pulse width modulation means supplied with said reference potential and with said DC voltage for developing a pulse width modulated output that varies with changes in voltage of said DC voltage source; and means for controlling the conduction duty cycle of said self-oscillating converter with the output of said low frequency pulse width modulation means whereby variable duration bursts of said high frequency energy at said low frequency rate are supplied to said fluorescent lamp.

Claim 13

A self-regulating power supply for a fluorescent lamp comprising: a parallel resonant self-oscillating converter for developing a high frequency, high voltage output for supplying a fluorescent lamp with high frequency energy from a DC voltage source that is subject to variation in voltage; low frequency pulse width modulation means coupled to said DC voltage source; means for developing a reference potential coupled to said DC voltage source; comparator means in said low frequency pulse width modulation means supplied with said reference potential and with said DC voltage for developing a pulse width modulated output that varies with changes in voltage of said DC voltage source; and means for controlling the conduction duty cycle of said self-oscillating converter with the output of said low frequency pulse width modulation means whereby variable duration bursts of said high frequency energy at said low frequency rate are supplied to said fluorescent lamp.