Electric ballast system

• US 6,215,255 B1
• Filed: 05/01/2000
• Issued: 04/10/2001
• Est. Priority Date: 04/30/1999
• Status: Expired due to Term

• Current Assignee: Semiconductor Components Industries LLC (ON Semiconductor Corporation)
• Original Assignee: Fairchild Korea Semiconductor Limited (ON Semiconductor Corporation)
• Inventors: Kim, Dae-Bong, Choi, Nak-Choon
• Primary Examiner(s): Philogene, Haissa
• Application Number:
  US09/561,679
• Time in Patent Office: 344 Days
• Field of Search: 315/209.R, 315/307, 315/224, 315/291, 315/244, 315/127, 315/DIG.4, 315/DIG.7
• US Class Current: 315/291
• CPC Class Codes: H05B 41/282 with semiconductor devices H05B41/2806, H05B41/288, H05B41/295 take precedence
• CPC Class Codes: H05B 41/2855 against abnormal lamp operating conditions
• CPC Class Codes: Y10S 315/04 Dimming circuit for fluorescent lamps

Abstract

Disclosed is an electric ballast system. The system comprises a voltage source for supplying power to the electric ballast system; a lamp driving circuit having a first terminal, a second terminal, and a third terminal, the power of the voltage source being supplied through the first terminal to begin the driving of the electric ballast system, and the lamp driving circuit outputting PWM waves through the second and third terminals; a half bridge converter, a first end of which is connected to the second terminal of the lamp driving circuit and a second end of which is connected to the third terminal of the lamp driving circuit, the half bridge converter receiving input through the second and third terminals of the lamp driving circuit, and the half bridge converter performing output of a current which changes flow directions according to the PWM waves output by the lamp driving circuit; a lamp portion, a first end of which is connected to an output end of the half bridge converter, the lamp operating according to the current output by the half bridge converter; and a lamp protector connected between a second end of the lamp and the first terminal of the lamp driving circuit, the lamp protector discontinuing the operation of the lamp driving circuit if there is no bulb installed in the lamp.

Claims

1. An electric ballast system comprising:

a voltage source for supplying power to the electric ballast system;

a lamp driving circuit having a first terminal, a second terminal, and a third terminal, the power of the voltage source being supplied through the first terminal to begin the driving of the electric ballast system, and the lamp driving circuit outputting PWM waves through the second and third terminals;

a half bridge converter, a first end of which is connected to the second terminal of the lamp driving circuit and a second end of which is connected to the third terminal of the lamp driving circuit, the half bridge converter receiving input through the second and third terminals of the lamp driving circuit, and the half bridge converter performing output of a current which changes flow directions according to the PWM waves output by the lamp driving circuit;

a lamp portion, a first end of which is connected to an output end of the half bridge converter, the lamp operating according to the current output by the half bridge converter; and

a lamp protector connected between a second end of the lamp and the first terminal of the lamp driving circuit, the lamp protector discontinuing the operation of the lamp driving circuit if there is no bulb installed in the lamp.

2. The electric ballast system of claim 1 further comprising:

a first resistor connected between the voltage source and the first terminal of the lamp driving circuit;

a first capacitor connected between a ground and a common terminal of a first resistor and the first terminal of the lamp driving circuit, the first capacitor being charged by a current input through the first resistor; and

a first diode connected between a ground and a common terminal of a third capacitor and the first terminal of the lamp driving circuit, the first diode acting to maintain a charge voltage of the third capacitor above a predetermined potential.

3. The electric ballast system of claim 1 wherein the lamp driving circuit comprises:

a reference current generator for generating and outputting a reference current;

a lamp drive starter for receiving the power of the voltage source through the first terminal of the lamp driving circuit to begin the operation of the lamp driving circuit;

a soft starter receiving a starting signal from the lamp drive starter and the reference current from the reference current generator, and outputting a lamp initial drive current to soft start the lamp;

a sawtooth wave oscillator for outputting a sawtooth wave current;

an adder receiving the lamp initial drive current from the soft starter and the sawtooth wave current from the sawtooth wave oscillator, and adding the lamp initial drive current to the sawtooth wave current and outputting a resulting output current;

a first current source connected to the adder to receive the output current of the adder, the first current source selectively dividing the output current of the adder;

a PWM wave generator connected to a common terminal of the adder and the first current source, receiving the output current of the adder, and generating and outputting output PWM waves; and

a PWM wave splitter receiving the output PWM waves from the PWM wave generator, and alternatingly splitting and outputting the PWM waves through the second and third terminals of the lamp driving circuit.

4. The electric ballast system of claim 3 further comprising:

a second capacitor connected between the soft starter and a ground, the second capacitor determining a soft starting time;

a third capacitor connected between a ground and a common terminal of the adder and the PWM wave generator, the third capacitor determining a frequency of the PWM waves; and

a second resistor connected between the reference current generator and a ground, the second resistor determining a magnitude of the reference current output by the reference current generator.

5. The electric ballast system of claim 4 wherein the soft starter comprises:

a first switch connected between a ground and the second capacitor, the first switch being controlled to ON if the starting signal of the lamp drive starter is generated, thereby reducing a charge voltage of the second capacitor;

a subtractor connected to a common terminal of the first switch and the second capacitor, the subtractor obtaining a difference between a reference voltage and the charge voltage of the second capacitor, and outputting an output voltage corresponding to the difference; and

a multiplier receiving the output voltage of the subtractor and the reference current of the reference current generator, and multiplying the output voltage of the subtractor to the reference current of the reference current generator.

6. The electric ballast system of claim 5 wherein the PWM wave generator comprises:

a first comparator receiving a charge voltage of the third capacitor through a first terminal and a first potential through a second terminal, comparing the charge voltage of the third capacitor with the first potential, and outputting a comparison value;

a second comparator receiving the charge voltage of the third capacitor through a second terminal and a second potential through a first terminal, comparing the charge voltage of the third capacitor with the second potential, and outputting a comparison value; and

a latch receiving the output value of the first comparator and the output value of the second comparator, and outputting a latching value.

7. The electric ballast system of claim 1 wherein the half bridge converter comprises:

a transformer having a primary coil, a first end of the primary coil being connected to the second terminal of the lamp driving circuit and a second end of the primary coil being connected to the third terminal of the lamp driving circuit, and having first and second secondary coils through which the PWM waves of the lamp driving circuit are alternatingly output;

a first MOSFET transistor having a source connected to the voltage source, a gate connected to a first end of the first secondary coil of the transformer, and a drain connected to a second end of the first secondary coil of the transformer, the first MOSFET transistor performing switching according to an output waveform of the first secondary coil of the transformer; and

a second MOSFET transistor having a drain connected to a common terminal of the drain of the first MOSFET transistor and the first secondary coil of the transformer, a gate connected to a first end of the second secondary coil of the transformer, and a source connected to a second end of the second secondary coil of the transformer, the second MOSFET transistor performing switching according to an output waveform of the second secondary coil of the transformer.

8. The electric ballast system of claim 7 further comprising:

a third resistor connected between the first secondary coil of the transformer and the gate of the first MOSFET transistor, the third resistor preventing an excess current from flowing to the first MOSFET transistor; and

a fourth resistor connected between the second secondary coil of the transformer and the gate of the second MOSFET transistor, the fourth resistor preventing an excess current from flowing to the second MOSFET transistor.

9. The electric ballast system of claim 8 wherein the lamp portion comprises:

an inductor connected to a common terminal of the first MOSFET transistor and the second MOSFET transistor;

a lamp, a first end of which is connected to the inductor;

a fourth capacitor connected in parallel to the lamp;

a fifth capacitor connected between a second end of the lamp and a common terminal of the voltage source and the first MOSFET transistor; and

a sixth capacitor connected between the source of the second MOSFET transistor and a common terminal of the second end of the lamp and the fifth capacitor.

10. The electric ballast system of claim 9 wherein the lamp protector comprises:

a seventh capacitor, one end of which is connected to a common terminal of the fifth capacitor and the sixth capacitor;

a second diode having a cathode connected to the seventh capacitor, and an anode connected to a common terminal of the source of the second MOSFET transistor and the sixth capacitor; and

a third diode having an anode connected to a common terminal of the seventh capacitor and the cathode of the second diode, and a cathode connected to the first terminal of the lamp driving circuit.