CONTROL CIRCUIT FOR PROVIDING REGULATED CURRENT TO LAMP LOAD

• US 3,611,021 A
• Filed: 04/06/1970
• Issued: 10/05/1971
• Est. Priority Date: 04/06/1970
• Status: Expired due to Term

• Current Assignee: ITT Corporation (ITT, Inc.)
• Original Assignee: Kenneth A. Wallace
• Inventors: Wallace, Kenneth A.
• Primary Examiner(s): Lake, Roy
• Assistant Examiner(s): Demeo, Palmer C.
• Application Number:
  US05/025,684
• Time in Patent Office: 547 Days
• Field of Search: 315/DIG.5,DIG.2,307,239 331/113A
• US Class Current: 315/239
• CPC Class Codes: H02M 7/53806 in a push-pull configuration of the parallel type
• CPC Class Codes: H05B 41/392 using semiconductor devices, e.g. thyristor
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp

Abstract

Control circuit for gaseous discharge lamps including a variable frequency inverter for driving a high-reactance transformer having a first capacitor in the transformer secondary tuned to a harmonic of the supply voltage to provide ignition voltage for the lamps, and a second capacitor in near series resonance with the fundamental frequency of the supply voltage to provide series impedance at the fundamental frequency for stable operation after ignition, and lamp current sensing means for providing a feedback signal to a variable reference comparator circuit which adjusts the frequency output of the inverter to provide regulated lamp current for changes in input voltage and lamp voltage.

Claims

1. A control circuit for providing regulated current to a gaseous lamp comprising an input circuit over which direct current power is supplied, a variable frequency inverter circuit connected to said input means including a control input for adjusting the frequency of the output signals from said inverter circuit, a high-reactance transformer having a primary and a secondary winding, means connecting said primary winding to the output of said variable frequency inverter, a further winding means on said transformer connected to energize the filaments of said lamp, a shunt capacitor connected in shunt of said secondary winding for providing harmonic resonance during start, a series capacitor connected in series with said secondary winding and said gaseous lamp to provide fundamental resonance for lamp energization subsequent to start, and lamp current regulating means for providing a control signal to said control input to adjust the frequency output of said variable frequency inverter circuit in a current regulating mode.

2. A circuit as set forth in claim 1 in which said lamp current regulating means includes a sensing circuit for providing a signal representative of the value of the lamp current, a rEference circuit for providing a preset reference signal level, and means for providing a control signal to said variable frequency inverter circuit of a magnitude related to the differential of the sensed signal relative to said preset reference signal level.

3. A circuit as set forth in claim 2 in which said reference circuit includes means for adjusting said preset reference to different values.

4. A circuit as set forth in claim 1 in which said variable frequency inverter circuit includes an oscillator circuit and a pair of switching transistors driven by said oscillator circuit, and in which said control signal is fed to said control input to vary the output frequency of said inverter circuit to maintain a constant output current and thereby a constant light intensity from said lamp.

5. A control circuit as set forth in claim 4 in which said oscillator circuit is a saturable core oscillator.

6. A control circuit as set forth in claim 1 in which said series capacitor and said secondary winding of said transformer have a value which establishes the operating frequency of the variable frequency inverter circuit to be above the starting frequency of the inverter circuit.

7. A control circuit as set forth in claim 6 in which said control signal to said variable frequency inverter circuit increases the inverter output frequency to reduce lamp current responsive to detection of an increase in lamp current by said lamp current regulating means.

8. A control circuit as set forth in claim 1 in which said series capacitor and said secondary winding of said transformer has a value which establishes the operating frequency to occur below the starting frequency of the variable frequency inverter circuit.

9. A control circuit as set forth in claim 8 in which said control signal to said variable frequency inverter circuit decreases the inverter output frequency to decrease the lamp current in response to the detection of an increase in lamp current by said lamp current regulating means.

10. A control circuit as set forth in claim 1 in which said shunt capacitor is connected across only a part of said secondary winding.

11. A control circuit as set forth in claim 1 in which said primary and secondary transformer windings are connected in an autotransformer configuration with the primary voltage in series with the secondary voltage, and said shunt capacitor is connected across the secondary winding and said series capacitor is connected in series with the parallel connected secondary winding and shunt capacitor.

12. A control circuit as set forth in claim 1 in which said transformer and frequency inverter circuit have components which provide a lamp current at the starting frequency which is slightly higher than the maximum desired lamp current for the minimum input voltage over said input circuit and the maximum drop across said lamp.

13. A control circuit as set forth in claim 1 in which the signal output of said adjustable frequency inverter current comprises an AC square wave having a fundamental frequency component plus one or more harmonics.

14. A control circuit as set forth in claim 1 in which said lamp current regulating means comprises a current transformer having a primary winding connected in series with said lamp, and a center tapped secondary winding, a rectifier circuit connected to the output of said secondary winding, and a resistor connected to the output of said rectifier circuit to develop a DC signal representative of the current in said lamp circuit.

15. A control circuit as set forth in claim 1 in which said frequency circuit operates at a first frequency for ignition of said lamp and a second frequency for operation of said lamp, and wherein a momentary interruption of lamp power during operation of said lamp and a resulting loss of lamp current causes said lamp current regulating means to provide a control input signal to return the variable frequency inverter circuit from said second operating frequency to said fIrst starting frequency for reignition of said lamp.