Power feedback power factor correction scheme for multiple lamp operation

• US 20020011801A1
• Filed: 01/21/2000
• Published: 01/31/2002
• Est. Priority Date: 01/21/2000
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Chang, Chin
• Granted Patent: US 6,429,604 B2
• Time in Patent Office: Days
• US Class Current: 315/219
• CPC Class Codes: H05B 41/28 using static converters
• CPC Class Codes: H05B 41/2827 using specially adapted components in the load circuit, e.g. feed-back transformers, piezoelectric transformers; using specially adapted load circuit configurations
• CPC Class Codes: H05B 45/355 Power factor correction [PFC]; Reactive power compensation
• CPC Class Codes: Y10S 315/07 Starting and control circuits for gas discharge lamp using transistors

Abstract

A ballast circuit for a single or multiple lamp parallel operation where at each lamp a condition may be controlled such that the amplitude of a resonant inductor current and an output voltage are almost constant in the steady state. The inventive circuit consists of a half-bridge of a DC storage capacitor, a DC blocking capacitor, power transistors which alternatively switch on and off and having 50% duty ratio, and an LLC resonant converter having a resonant inductor and one or more resonant capacitors. The inventive circuit consists of an output transformer providing galvanic isolation for a double path type power feedback scheme. The output transformer produces magnetizing inductance utilized for power feedback circuit optimization and is inserted right after the resonant inductor of the half-bridge circuit.

Claims

1. A ballast circuit for a parallel operation of at least one lamp, each of said at least one lamp having a ballasting capacitor, said circuit operating in high frequency cycles, said circuit comprising:

one or more power transistors to generate a resonant inductor current;

a LLC resonant converter comprising a resonant inductor, an output transformer having magnetizing inductance, and at least one resonant capacitor, a part of said LLC resonant converter forming a resonant tank circuit for generating a first voltage;

said output transformer providing galvanic isolation for generating a second voltage, said resonant inductor being disposed between said output transformer on its first side and said one resonant capacitor on its second; and

said at least one lamp having a third voltage via said ballasting capacitor.

2. The circuit of claim 1, wherein a condition is controlled such that amplitudes of said third voltage are held constant in a steady state for said one or more lamps.

3. The circuit of claim 2, further comprising a first capacitor, whereby said resonant inductor current charges and discharges said first capacitor.

4. The circuit of claim 3, wherein a phase difference exists between said second voltage and said resonant inductor current.

5. The circuit of claim 4, wherein a condition is controlled such that an amplitude of said resonant inductor current and said third voltage are constant in said steady state for said one or more lamps.

6. The circuit of claim 5, wherein in each of said high frequency cycles, said circuit conducts current twice.

7. The circuit of claim 6, wherein said power transistors generate said resonant inductor current by alternatively switching on and off, said power transistors having 50% duty ratio.

8. The circuit of claim 6, wherein said output transformer produces magnetizing inductance.

9. The circuit of claim 8, further comprising a power feedback circuit, whereby said magnetizing inductance is utilized to optimize said power feedback circuit.

10. The circuit of claim 9, further comprising:

an input line filter having an inductor and a capacitor, said input line filter filters an input current to approach a sinusoidal waveform with a low THD;

a current rectifying circuit comprising a plurality of diodes;

a plurality of fast reverse recovery diodes; and

a DC storage capacitor and a DC blocking capacitor.

11. The circuit of claim 10, wherein said power feedback circuit of said resonant tank produces in said input current a power factor unique for differing number of lamps.

12. The circuit of claim 11, wherein a fourth voltage of said resonant tank is under 220.

13. The circuit of claim 12, wherein said circuit is operated at a first frequency where for each of said differing number of lamps a fourth voltage is kept under 220 Volts.

14. The circuit of claim 13, wherein for each of said differing number of lamps, an operating frequency is kept constant without line frequency modulation.

15. A ballast circuit for a parallel operation of multiple lamps, each of the lamps having a ballasting capacitor, said circuit comprising:

a power feedback circuit; and

a LLC resonant converter comprising a resonant inductor connected on one side to an output transformer having magnetizing inductance, and connected on the other side to at least one resonant capacitor, a part of said LLC resonant converter forming a resonant tank circuit for generating a first voltage, said resonant tank circuit allowing said power feedback circuit to produce reasonable power factor in said input current of the ballast circuit for differing number of said multiple lamps and keeping a DC bus voltage under 220 Volts for said differing number of said multiple lamps.