# US 5,703,439 A · Lamp power supply circuit with electronic feedback circuit for switch control

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- Number: US 5,703,439 A
- Document ID: US5703439A
- Status: Granted
- Kind: A
- Application number: 08/644,466
- Filed: 1996-05-10
- Granted: 1997-12-30
- Earliest claimed: 1996-05-10
- Assignees: General Electric Company
- Inventors: Louis R. Nerone
- Web page: https://patentgrep.com/patent/US5703439A

## CPC

- H05B 41/2827: {using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations}
- H05B 41/2828: {using control circuits for the switching elements (H05B41/2827 takes precedence)}
- H05B 41/2856: {against internal abnormal circuit conditions}
- H05B 41/3925: {by frequency variation (H05B41/3922 takes precedence)}
- Y02B 20/00: Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
- Y10S 315/07: Starting and control circuits for gas discharge lamp using transistors
- H05B: ELECTRIC HEATING; ELECTRIC LIGHT SOURCES NOT OTHERWISE PROVIDED FOR; CIRCUIT ARRANGEMENTS FOR ELECTRIC LIGHT SOURCES, IN GENERAL
- Y02B: CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

Disclosed is a ballast circuit for a gas discharge lamp, including a resonant load circuit with a gas discharge lamp and first and second resonant impedances whose values determine the operating frequency of the resonant load circuit. The ballast circuit further includes a d.c.-to-a.c. converter circuit coupled to the resonant load circuit so as to induce an a.c. current in the resonant load circuit. The converter circuit comprises first and second switches serially connected between a bus conductor at a d.c. voltage and ground, and has a common node through which the bidirectional load current flows. A feedback arrangement regeneratively controls the first and second switches, and includes a circuit for sensing a.c. current in the resonant load circuit and producing a feedback signal in proportion to the a.c. current. The feedback arrangement includes a comparator circuit for comparing the feedback signal with a periodic reference signal, and for producing a comparator output signal that changes state when a first one of the compared signals becomes greater than the second of the compared signals, and that further changes state when the second of the compared signals then becomes greater than the first of the compared signals. Further included in the feedback arrangement is a circuit for generating the periodic reference signal in response to the comparator output signal, and a conditioning circuit receptive of the comparator output signal for controlling the first and second switches.

## Claims

### Claim 1

A ballast circuit for a gas discharge lamp, comprising:
(a) a resonant load circuit incorporating a gas discharge lamp and including first and second resonant impedances whose values determine the operating frequency of said resonant load circuit;
(b) a d.c.-to-a.c. converter circuit coupled to said resonant load circuit so as to induce an a.c. current in said resonant load circuit, and comprising first and second switches serially connected between a bus conductor at a d.c. voltage and ground, and having a common node through which said bidirectional load current flows; and
(c) a feedback arrangement for regeneratively controlling said first and second switches; said arrangement including a circuit for sensing a.c. current in said resonant load circuit and producing a feedback signal in proportion to said a.c. current; said feedback arrangement further including:
(i) a comparator circuit for comparing said feedback signal with a periodic reference signal, and for producing a comparator output signal that changes state when a first one of the compared signals becomes greater than the second of the compared signals, and that further changes state when the second of the compared signals then becomes greater than the first of the compared signals;
(ii) a circuit for generating said periodic reference signal in response to said comparator output signal; and
(iii) a conditioning circuit receptive of said comparator output signal for controlling said first and second switches.

### Claim 2 (depends on 1)

The ballast circuit of claim 1, wherein said conditioning circuit includes a dead time circuit for creating a dead time interval just prior to said first switch being turned on when both said first and second switches are off, and just prior to said second switch being turned on when both said first and second switches are off.

### Claim 3 (depends on 2)

The ballast circuit of claim 2, where said dead time circuit includes means for selecting the duration of said dead times intervals from a range of choices.

### Claim 4 (depends on 1)

The ballast circuit of claim 1, wherein said circuit for generating said periodic reference signal includes means for selecting the magnitude of current in the lamp from a range of choices.

### Claim 5 (depends on 1)

The ballast circuit of claim 1, wherein said circuit for generating a periodic reference signal is effective for producing a substantially triangular reference waveform whose excursions above a reference axis of strength are substantially mirror-images of excursions of the foregoing signal below said reference axis, although shifted in time with respect to each other.

### Claim 6 (depends on 5)

The ballast circuit of claim 5, wherein:
(a) said circuit for producing a feedback signal is effective for producing a feedback waveform whose excursions above a reference axis of strength are substantially mirror-images of excursions of said signal below the foregoing reference axis, although shifted in time with respect to each other; and
(b) the mentioned reference axes of strength of said periodic reference signal and of said feedback signal are approximately equal to each other.

### Claim 7 (depends on 1)

The ballast circuit of claim 1, wherein said circuit for sensing the a.c. current in said resonant load circuit, and producing a feedback signal, comprises a resistance in said resonant load circuit.

### Claim 8

A ballast circuit for a gas discharge lamp, comprising:
(a) a resonant load circuit including a gas discharge lamp and first and second resonant impedances whose values determine the operating frequency of said resonant load circuit;
(b) a d.c.-to-a.c. converter circuit coupled to said resonant load circuit so as to induce an a.c. current in said resonant load circuit, and comprising first and second power switches serially connected between a bus conductor at a d.c. bus voltage and ground, and having a common node through which the a.c. load current flows; and
(c) a feedback arrangement for regeneratively controlling said first and second switches; said arrangement including a circuit for sensing a.c. current in said resonant load circuit and producing a feedback signal in proportion to said a.c. current; said feedback arrangement further including:
(i) a comparator circuit for comparing said feedback signal with a periodic reference signal, and for producing a comparator output signal that changes state when a first one of the compared signals becomes greater than the second of the compared signals, and that further changes state when the second of the compared signals then becomes greater than the first of the compared signals;
(ii) a circuit for generating said periodic reference signal including means, responsive to said comparator output signal, for causing transitions from a predominantly higher-going portion to a predominantly lower-going portion of said periodic reference signal, and vice-versa; and
(iii) a conditioning circuit receptive of said comparator output signal for controlling said first and second switches.

### Claim 9 (depends on 8)

The ballast circuit of claim 8, wherein said circuit for generating said periodic reference signal comprises a delay circuit for delaying transitioning between said predominantly higher-going portion and said predominantly lower-going portion of said periodic reference signal, so as to assure a stable change of output state of the comparator circuit.

### Claim 10 (depends on 8)

The ballast circuit of claim 8, wherein said conditioning circuit includes a dead time circuit for creating a dead time interval just prior to said first switch being turned on when both said first and second switches are off, and just prior to said second switch being turned on when both said first and second switches are off.

### Claim 11 (depends on 10)

The ballast circuit of claim 10, where said dead time circuit includes means for selecting the duration of said dead times intervals from a range of choices.

### Claim 12 (depends on 8)

The ballast circuit of claim 8, wherein said circuit for generating said periodic reference signal includes means for selecting the magnitude of current in the lamp from a range of choices.

### Claim 13 (depends on 8)

The ballast circuit of claim 8, wherein:
(a) said circuit for producing a feedback signal is effective for producing a feedback waveform having excursions above a reference axis of strength that are substantially mirror-images of excursions of said signal below the foregoing reference axis, although shifted in time with respect to each other;
(b) said circuit for generating a periodic reference signal is effective for producing a substantially triangular reference waveform having excursions above a reference axis of strength that are substantially mirror-images of excursions of said reference triangular waveform below the said reference axis, although shifted in time with respect to each other; and
(c) the mentioned reference axes of strength of said feedback signal and of said periodic reference signal are approximately equal to each other.

### Claim 14 (depends on 8)

The ballast circuit of claim 8, wherein said circuit for generating said periodic reference signal includes means for selecting the magnitude of current in the lamp from a range of choices.

### Claim 15 (depends on 8)

The ballast circuit of claim 8, wherein said circuit for generating a periodic reference signal comprises:
(a) a capacitor whose voltage comprises said periodic reference signal;
(b) a resistor having one end coupled to said capacitor and another end coupled to said bus conductor; and
(c) a switch serially coupled between said capacitor and said resistor and whose switching state is responsive to said comparator output signal.

### Claim 16 (depends on 15)

The ballast circuit of claim 15, wherein said circuit for generating a periodic reference signal further comprises a delay circuit for delaying turn on of said switch coupled between said capacitor and said resistor in response to said comparator output signal, so as to assure a stable change of output state of the comparator circuit.