Power supply for fluorescent lamp

Claim 2

A lighting system comprising: a source of electrical power; means for converting the electrical power from the source into rectangular waves; a parallel tank circuit resonant near the fundamental or a harmonic of the frequency of the rectangular waves; a fluorescent lamp having first and second electrodes, the lamp having high impedance while starting and low impedance after starting; means for connecting the tank circuit between the first and second electrodes of the lamp; and means for magnetically coupling the converting means to the tank circuit to apply the electrical power across the first and second electrodes of the lamp, the coupling means having sufficiently loose coupling to prevent the low impedance of the lamp after starting from loading the converting means.

Claim 3

The lighting system of claim 1, in which the coupling means comprises: a core with first and second core segments, the ends of the core segments being spaced apart to form gaps that produce loose coupling; primary winding means that is part of the converting means and secondary winding means that is part of the parallel tank circuit wound around the core, the rectangular waves of the converting means being impressed across the primary winding means.

Claim 4

The lighting system of claim 1, in which at least one of the first and second electrodes of the fluorescent lamps has a pair of terminals across which an electrical potential is applied to heat the electrodes while starting the lamp, the connecting means applying the electrical power across the first and second electrodes while starting the lamp and after starting the lamp, and also applying the electrical power across the one pair of terminals while starting the lamp and after starting the lamp, the ratio of voltage across the first and second electrodes while starting the lamp and after starting the lamp, and also applying the electrical power across the one pair of terminals while starting the lamp and after starting the lamp, the ratio of voltage across the first and second electrodes to the voltage across the one pair of terminals being such as to prevent arcing between the one pair of terminals and arcing between the first and second electrodes while properly heating the electrodes and non-destructively starting the lamp.

Claim 5

The lighting system of claim 1, in which the tank circuit has resonant at a frequency slightly lower than the fundamental frequency of the rectangular waves.

Claim 6

The lighting system of claim 1, in which the source of electrical power is alternating current at a first frequency, and the converting means converts the electrical power to a second frequency higher than the first frequency.

Claim 7

The lighting system of claim 1, in which the converting means comprises first and second transistors and means for alternatively saturating and cutting off the first and second transistors without magnetically saturating the coupling means.

Claim 8

The lighting system of claim 1, in which the source has first and second output terminals, the first and second electrodes each have two terminals, and the connecting means comprises: a selector switch having a movable contact and at least first and second stationary contacts; an autotransformer having first and second end taps, a first intermediate tap near the first end tap, a second intermediate tap near the second end tap, and a third intermediate tap between the first and second intermediate taps; means for connecting the first output terminal to the movable contact; means for connecting the first stationary contact to the first end tap; means for connecting the second output terminal to the second end tap; means for connecting the second stationary contact to the third intermediate tap; means for connecting the first end tap to one terminal of the first electrode; means for connecting the first intermediate tap to the other terminal of the first electrode; means for connecting the second intermediate tap to one terminal of the second electrode; and means for connecting the second end tap to the other terminal of the second electrode.

Claim 9

A lighting system comprising: a source of electrical power; a fluorescent lamp having first and second electrodes each with a pair of terminals across which an electrical potential is applied to heat the electrodes while starting the lamp; first means for applying power from the source across the first and second electrodes while starting the lamp and after starting the lamp; and second means for applying power from the source across at least one pair of terminals while starting the lamp and after starting the lamp, the ratio of voltage across the first and second electrodes to the voltage across the one pair of terminals being such as to prevent arcing between the one pair of terminals and arcing between the first and second electrodes.

Claim 10

A lighting system comprising: a source of electrical power; a fluorescent lamp having first and second electrodes each with a pair of terminals across which an electrical potential is applied to heat the electrodes while starting the lamp; first means for applying power from the source across the first and second electrodes while starting the lamp and after starting the lamp; and second means for applying power from the source across at least one pair of terminals while starting the lamp and after starting the lamp, the ratio of voltage across the first and second electrodes to the voltage across the one pair of terminals being such as to prevent arcing between the one pair of terminals and arcing between the first and second electrodes.

Claim 11

The lighting system of claim 8, in which the source has first and second output terminals and the first and second applying means comprises: a selector switch having a movable contact and at least first and second stationary contacts; an autotransformer having first and second end taps, a first intermediate tap near the first end tap, a second intermediate tap near the second end tap, and a third intermediate tap between the first and second intermediate taps; first means for connecting the first output terminal to the movable contact; second means for connecting the first stationary contact to the first end tap; third means for connecting the second output terminal to the second end tap; fourth means for connecting the second stationary contact to the third intermediate tap; fifth means for connecting the first end tap to one terminal of the first electrode; sixth means for connecting the first intermediate tap to the other terminal of the first electrode; seventh means for connecting the second intermediate tap to one terminal of the second electrode; and eighth means for connecting the second end tap to the other terminal of the second electrode.

Claim 12

The lighting system of claim 9, in which pulsating power at a given frequency appears across the first and second output terminals and the first and third connecting means comprise: a transformer having a primary winding connected across the first and second output terminals and a secondary winding across which the movable contact and the second end tap are connected; and a tuning capacitor connected in parallel with the secondary winding to resonate near the given frequency of the electrical power.

Claim 13

The lighting system of claim 10, additionally comprising a capacitor connected between the first and second end taps to increase the effective capacitance in parallel with the secondary winding when the movable contact engages the second stationary contact.

Claim 14

The lighting system of claim 11, in which the primary winding is part of a converter for increasing the frequency of the pulsating electrical power.

Claim 15

A power supply for a fluorescent lamp comprising: a rectifier having a pair of input terminals adapted to receive alternating current power from a source of line voltage, a high voltage output terminal and a low voltage output terminal; a transformer having a first primary winding, a second primary winding, a feedback winding, and a secondary winding on a common core; a first transistor having a base, a collector connected by the first primary winding to the high voltage output terminal of the rectifier, and an emitter connected to the low voltage output terminal of the rectifier; a second transistor having a base, a collector connected by the second primary winding to the high voltage output terminal of the rectifier, and an emitter connected to the low voltage output terminal of the rectifier; biasing resistor means connnected between the high voltage output terminal of the rectifier and the bases of the first and second transistors; means for connecting the feedback winding between the bases of the first and second transistors; and timing means for causing the first and second transistors to alternately saturate and cut off wth short transition times to produce rectangular waves across the primary windings; a tuning capacitor connected in parallel with the secondary winding, the secondary winding and the tuning capacitor being resonant approximately at the frequency of the fundamental or a harmonic of the rectangular waves produced across the primary windings; first and second lamp energizing output terminals; means for coupling the secondary winding and tuning capacitor in parallel across the first and second output terminals; and the coupling coefficient of the core being sufficiently small so loading of the lamp energizing output terminals has no substantial effect on the transition times of the first and second transistors between saturation and cut off.

Claim 16

A power supply for a fluorescent lamp comprising: a rectifier having a pair of input terminals adapted to receive alternating current power from a source of line voltage, a high voltage output terminal and a low voltage output terminal; a transformer having a first primary winding, a second primary winding, a feedback winding, and a secondary winding on a common core; a first transistor having a base, a collector connected by the first primary winding to the high voltage output terminal of the rectifier, and an emitter connected to the low voltage output terminal of the rectifier; a second transistor having a base, a collector connected by the second primary winding to the high voltage output terminal of the rectifier, and an emitter connected to the low voltage output terminal of the rectifier; biasing resistor means connnected between the high voltage output terminal of the rectifier and the bases of the first and second transistors; means for connecting the feedback winding between the bases of the first and second transistors; and timing means for causing the first and second transistors to alternately saturate and cut off wth short transition times to produce rectangular waves across the primary windings; a tuning capacitor connected in parallel with the secondary winding, the secondary winding and the tuning capacitor being resonant approximately at the frequency of the fundamental or a harmonic of the rectangular waves produced across the primary windings; first and second lamp energizing output terminals; means for coupling the secondary winding and tuning capacitor in parallel across the first and second output terminals; and the coupling coefficient of the core being sufficiently small so loading of the lamp energizing output terminals has no substantial effect on the transition times of the first and second transistors between saturation and cut off.

Claim 17

The power supply of claim 13, additionally comprising: third and fourth lamp energizing output terminals; first means for applying between the first and third output terminals a portion of the voltage between the first and second output terminals; and second means for applying between the second and fourth output terminals a portion of the voltage between the first and second output terminals.

Claim 18

The power supply of claim 14, in which the first applying means comprises an intermediate tap on the secondary winding connected to the third output terminal.

Claim 19

The power supply of claim 15, in which the second applying means comprises means for connecting the low voltage output terminal of the rectifier to the fourth output terminal and means for connecting the emitters of he transistors to the second output terminal.

Claim 20

The power supply of claim 16, additionally comprising capacitor means connected in parallel between the high and low output terminals of the rectifier, the capacitance of the capacitor means presenting a short circuit across the high and low output terminals of the rectifier at the frequency of the square wave.

Claim 21

The power supply of claim 17, in which the connecting means comprises a first filter capacitor and a second filter capacitor in parallel, the second filter capacitor being connected between the high output terminal of the rectifier and the emitters of the transistors.

Claim 22

The power supply of claim 18, in which the means for coupling the secondary winding and the tuning capacitor in parallel across the first and second output terminals comprises: a multi-position switch having a movable contact arm engageable with a plurality of stationary contacts; an autotransformer having a number of spaced taps exceeding the plurality of stationary contacts by one; means connecting the junction of the tuning capacitor and the secondary winding to one of the taps of the autotransformer; means for connecting the stationary contacts to the remaining taps of the autotransformer, respectively; means for connecting the other junction of the tuning capacitor and the secondary winding to the movable contact arm; means for connecting the one tap of the autotransformer to the second output terminal; means for connecting another of the taps of the autotransformer to the first output terminal to vary the voltage applied between the first and second output terminals depending upon the stationary contact engaged by the movable contact arm.

Claim 23

The power supply of claim 13, additionally comprising a first diode connected between the emitter and base of the first transistor, the first diode being poled for conduction in a direction opposite to the emitter-to-base junction of the first transistor, and a second diode connected between the emitter and base of the second transistor, the second diode being poled for conduction in a direction opposite to the emitter-to-base junction of the second transistor.

Claim 24

The power supply of claim 13, in which the timing means comprises a timing capacitor and a charging resistor connected in series with the feedback winding between the bases of the first and second transistors.

Claim 25

The power supply of claim 13, in which the timing means comprises a first SCR having a gating electrode, the first SCR being connected between and poled for current flow in the same direction as the base and emitter of the first transistor, a first voltage generating resistor connected between the emitter of the first transistor and the low voltage output terminal, means for connecting the junction of the emitter of the first transistor and the first resistor to the gating electrode of the first SCR to fire the first SCR when the current through the first transistor exceeds a predetermined value, a second SCR having a gating electrode, the second SCR being connected between and poled for current flow in the same direction as the base and emitter of the second transistor, a second voltage generating resistor connected between the emitter of the second transistor and the low voltage output terminal, and means for connecting the junction of the emitter of the second transistor and the second resistor to the gating electrode of the second SCR to fire the second SCR when the current through the second transistor exceeds a predetermined value.

Claim 26

The power supply of claim 13, additionally comprising: means for sensing the current applied to the first and second output terminals; and means responsive to the sensing means for adjusting the timing means to reduce the power applied to the first and second output terminals as the sensed current increases.

Claim 27

The power supply of claim 23, in which the sensing means is an inductive current sensing winding connected in series with the first and second output terminals.

Claim 28

The power supply of claim 23, in which the timing means comprises a first SCR having a gating electrode, the first SCR being connected between and poled for current flow in the same direction as the base and emitter of the first transistor, a first voltage generating resistor connected between the emitter of the first transistor and the low voltage output terminal, a first inductive control winding magnetically coupled to the sensing winding and connecting the junction of the emitter of the first transistor and the first resistor to the gating electrode of the first SCR to fire the first SCR when the difference in current through the frst transistor and the sensing winding exceeds a predetermined value, a second SCR having a gating electrode, the second SCR being connected and poled for current flow in the same direction as the base and emitter of the second transistor, a second voltage generating resistor connected between the emitter of the second transistor and the low voltage output terminal, and a second inductive control winding magnetically coupled to the sensing winding and connecting the junction of the emitter of the second transistor and the second resistor to the gating electrode of the second SCR to fire the second SCR when the difference in current through the second transistor and the sensing winding exceeds a predetermined value.

Claim 29

The lighting system of claim 1, additionally comprising a lamp intensity selector switch and means responsive to the selector switch for shunting the tank circuit with different capacitances to vary the degree of timing thereof.

Claim 30

A lighting system comprising: a source of electrical power; a fluorescent lamp having first and second electrodes, the lamp having high impedance while starting and low impedance after starting; a power regulator coupling the source to the lamp adjustably to apply power from the source to the lamp, the regulator comprising a ringing choke oscillator having a frequency dependent upon an applied control voltage; means for sensing the current applied to the lamp by the regulator, the current sensing means comprising a current sensing winding connected in series between the regulator and the lamp; and means responsive to the sensing means for adjusting the regulator to reduce the power applied to the lamp as the sensed current increases, the adjusting means comprises means for generating a control voltage for the oscillator responsive to the current flowing through the winding.

Claim 31

A lighting system comprising: a source of electrical power; a fluorescent lamp having first and second electrodes, the lamp having high impedance while starting and low impedance after starting; a power regulator coupling the source to the lamp adjustably to apply power from the source to the lamp, the regulator comprising a ringing choke oscillator having a frequency dependent upon an applied control voltage; means for sensing the current applied to the lamp by the regulator, the current sensing means comprising a current sensing winding connected in series between the regulator and the lamp; and means responsive to the sensing means for adjusting the regulator to reduce the power applied to the lamp as the sensed current increases, the adjusting means comprises means for generating a control voltage for the oscillator responsive to the current flowing through the winding.

Claim 32

The lighting system of claim 27, additionally comprising a lamp intensity selector switch and means responsive to the selector switch for shunting the current sensing winding with different resistances to vary the regulator adjustment responsive to the current passing through the current sensing winding.

Claim 33

The lighting system of claim 27, in which the source has a high voltage output terminal and a low voltage output terminal, and the oscillator comprises a transformer having a first primary winding, a second primary winding, a feedback winding, and a secondary winding on a common core, a first transistor having a base, a collector connected by the first primary winding to the high voltage output terminal of the rectifier, and an emitter connected to the low voltage output terminal of the rectifier, a second transistor having a base, a collector connected by the second primary winding to the high voltage output terminal of the rectifier, and an emitter connected to the low voltage output terminal of the rectifier, biasing resistor means connected between the high voltage output terminal and the bases of the first and second transistors, means for connecting the feedback winding between the bases of the first and second transistors, and timing means for causing the first and second transistors to alternately saturate and cut off with short transition times to produce rectangular waves across the primary windings.

Claim 34

The lighting system of claim 29, in which the timing means comprises a first SCR having a gating electrode, the first SCR being connected between and poled for current flow in the same direction as the base and emitter of the first transistor, a first voltage generating resistor connected between the emitter of the first transistor and the low voltage output terminal, means for connecting the junction of the emitter of the first transistor and the first resistor to the gating electrode of the first SCR to fire the first SCR when the current through the first transistor exceeds a predetermined value, a second SCR having a gating electrode, the second SCR being connected between and poled for current flow in the same direction as the base and emitter of the second transistor, a second voltage generating resistor connected between the emitter of the second transistor and the low output terminal, and means for connecting the junction of the emitter of the second transistor and the second resistor to the gating electrode of the second SCR to fire the second SCR when the current through the second transistor exceeds a predetermined value.

Claim 35

The lighting system of claim 30, in which the first and second connecting means each comprise a control winding magnetically coupled to the current sensing winding to advance the firing of the SCR's.