Electric lamp and discharge devices: systems – Current and/or voltage regulation
Reexamination Certificate
2000-05-01
2001-04-10
Philogene, Haissa (Department: 2821)
Electric lamp and discharge devices: systems
Current and/or voltage regulation
C315S2090SC, C315S127000, C315S224000, C315SDIG004
Reexamination Certificate
active
06215255
ABSTRACT:
BACKGROUND OF THE INVENTION
(a) Field of the Invention
The present invention relates to an electric ballast system, and more particularly, to a control circuit for an electric ballast system.
(b) Description of the Related Art
Electric ballast systems perform the initial driving of a lamp and thereafter supply stable power to the lamp. The conventional electric ballast system is typically comprised of a DC-DC converter for supplying DC power, and a lamp driving circuit for controlling the driving of a lamp. In such a conventional ballast system, power is supplied to the lamp driving circuit from a point at which an upper switch and a lower switch of the DC-DC converter meet. That is, power is supplied from this point without passing through the lamp.
However, the supply of power to the lamp driving circuit in the manner described above has many drawbacks. In particular, during a soft start or dimming, driving frequencies of the lamp quicken and a dead time decreases. At this time, a capacitor for supplying power to the lamp driving circuit limits the dead time operation. That is, a voltage of the point between the switches does not become zero during switching as a result of the capacitor connected between the upper and lower switches of the DC-DC converter. Hence, zero voltage switching is not able to occur, a temperature of a switching MOSFET increases, and normal lamp operation becomes difficult.
Further, since power is supplied to the lamp driving circuit without passing through the lamp, if there is no bulb in the lamp, power is continuously supplied to the lamp driving circuit, causing the switching MOSFET to burn out. To prevent such a problem, a protection circuit must be additionally installed in the lamp driving circuit.
SUMMARY OF THE INVENTION
The present invention has been made in an effort to solve the above problems.
It is an object of the present invention to provide an electric ballast system which can operate normally without relation to changes in driving frequencies.
It is another object of the present invention to provide an electric ballast system which discontinues the operation of a lamp driving circuit when there is no bulb in a lamp such that an additional protection circuit is not required.
To achieve the above objects, the present invention provides 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.
According to a feature of the present invention, the electric ballast system further comprises 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 fourth resistor and the first terminal of the lamp driving circuit, the first capacitor being charged by a current input through the fourth 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.
According to another feature of the present invention, 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.
According to yet another feature of the present invention, the electric ballast system further comprises 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.
According to still yet another feature of the present invention, 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.
According to still yet another feature of the present invention, 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.
According to still yet another feature of the present invention, 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
Choi Nak-choon
Kim Dae-Bong
Blakely & Sokoloff, Taylor & Zafman
Fairchild Korea Semiconductor Ltd.
Philogene Haissa
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