Discharge lamp driving circuit having resonant circuit defining two resonance modes
First Claim
1. A discharge lamp driving circuit comprising:
- a rectifier for rectifying an AC voltage from an AC voltage source to give a DC voltage;
a smoothing capacitor for smoothing the DC voltage from said rectifier into a smoothed DC voltage;
an inverter including a switching element turning on and off at a high frequency for converting the smoothed DC voltage to provide a high frequency electric power;
a control circuit which provides a control signal for turning on and off said switching element to operate said inverter;
a load circuit including a discharge lamp and a resonant circuit connected to said inverter for applying the high frequency electric power from said inverter to said discharge lamp through said resonant circuit;
a capacitor connected to one end of said resonant circuit for varying the DC voltage of the output of the rectifier in accordance with a varying instantaneous value of said high frequency current or voltage appearing in the resonant circuit, said resonant circuit defining two resonance modes one including said capacitor and the other excluding said capacitor, and said resonant circuit changing said resonance modes from one to the other within one switching cycle of said switching element, said one resonance mode lasting over a varying period relative to the period of the other resonance mode in accordance with an instantaneous voltage level of said AC voltage source;
a ripple reducing circuit for providing a modulation signal which modulates said control signal to vary a timing of turning on and off said switching element within a certain range given to said control circuit in a direction of reducing ripples in an envelop of a lamp current being fed to said discharge lamp;
a conditional signal generating means which generates a conditional signal indicative of an external condition affecting the increase of the ripple of said lamp current; and
said ripple reducing circuit having means which modifies said modulation signal in consideration of said conditional signal such that said modulation signal can modulate said control signal to vary said timing of turning on an off said switching element within said range for reducing the otherwise increasing ripple.
5 Assignments
0 Petitions
Accused Products
Abstract
An improved discharge lamp driving circuit of a charge-pump type capable of suppressing a ripple in an envelop of a lamp current at the time of dimming the lamp or at a low environmental temperature. The circuit includes an inverter having switching elements Q1 and Q2 for converting a voltage across a smoothing capacitor Ce into a high frequency power which is applied through a resonant circuit to the discharge lamp Ld. A capacitor Cin is connected to one end of the resonant circuit to vary a DC voltage of the output of the rectifier in accordance with a varying instantaneous value of the high frequency current or voltage appearing in the resonant circuit. A control circuit is provided to give a control signal for alternately turning on and off the switching elements Q1 and Q2. A feedback circuit FB is provided to modulate the control signal within a permissible range given to the control circuit in such a manner as to adjust the timing of turning on and off the switching elements Q1 and Q2 in a feedback manner based upon a lamp current detected by a current sensor SI, for reducing the ripple in the lamp current. A mixer MX is included to compensate for the lamp current in consideration of a dimmer signal Dim of dimming the lamp in order to suppress the ripple which would otherwise increase due to the dimming of the lamp.
86 Citations
9 Claims
-
1. A discharge lamp driving circuit comprising:
-
a rectifier for rectifying an AC voltage from an AC voltage source to give a DC voltage; a smoothing capacitor for smoothing the DC voltage from said rectifier into a smoothed DC voltage; an inverter including a switching element turning on and off at a high frequency for converting the smoothed DC voltage to provide a high frequency electric power; a control circuit which provides a control signal for turning on and off said switching element to operate said inverter; a load circuit including a discharge lamp and a resonant circuit connected to said inverter for applying the high frequency electric power from said inverter to said discharge lamp through said resonant circuit; a capacitor connected to one end of said resonant circuit for varying the DC voltage of the output of the rectifier in accordance with a varying instantaneous value of said high frequency current or voltage appearing in the resonant circuit, said resonant circuit defining two resonance modes one including said capacitor and the other excluding said capacitor, and said resonant circuit changing said resonance modes from one to the other within one switching cycle of said switching element, said one resonance mode lasting over a varying period relative to the period of the other resonance mode in accordance with an instantaneous voltage level of said AC voltage source; a ripple reducing circuit for providing a modulation signal which modulates said control signal to vary a timing of turning on and off said switching element within a certain range given to said control circuit in a direction of reducing ripples in an envelop of a lamp current being fed to said discharge lamp; a conditional signal generating means which generates a conditional signal indicative of an external condition affecting the increase of the ripple of said lamp current; and said ripple reducing circuit having means which modifies said modulation signal in consideration of said conditional signal such that said modulation signal can modulate said control signal to vary said timing of turning on an off said switching element within said range for reducing the otherwise increasing ripple. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
-
Specification