Method for supplying a gas discharge lamp, and a ballast circuit for such lamp
AssigneeKoninklijke Philips Electronics N.V.
InventorRonald Hans Van Der Voort
Life of this patent
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Abstract
A method and a ballast circuit to supply a gas discharge lamp by a high frequency voltage, which, by using a voltage controlled first generator (4), is generated from a substantial sinusoidal mains voltage of a lower mains frequency provided by a main source. A control loop is used which comprises a second generator (10) for providing a reference waveform signal having a frequency of and being synchronized with a supply voltage. The reference signal is compared with a measurement current signal (im), which is representative for a supply current to the lamp, to provide an error signal. The error signal modulates the frequency of the high frequency voltage such that the error signal is minimized.
Claims13
A method for supplying a gas discharge lamp from a main source of a substantial sinusoidal low frequency mains voltage, comprising:
- rectifying the mains voltage to provide a rectified voltage;
- generating an inverter control signal of a high frequency;
- modulating the frequency of the inverter control signal by a modulating signal to provide a modulated inverter control signal;
- inverting the rectified voltage by the modulated inverter control signal to an inverter output voltage having the frequency of the modulated inverter control signal;
- supplying the inverter output voltage to the lamp through a tank circuit;
- characterized by,
- measuring a current which is representative for a current supplied by the main source to provide a current measurement signal (im);
- generating a reference waveform signal with a frequency of and being synchronized with a supply voltage which corresponds to the measured current;
- comparing the reference waveform signal and the current measurement signal to provide a first error signal;
- and
- using the first error signal as the modulating signal, such that the error signal is minimized.
Method according to 1, characterized in that, a nominal frequency representing a frequency of the modulated inverter at a zero crossing of a mains voltage control signal is about identical to a resonance frequency of a circuit comprising the lamp and the tank circuit.
A ballast circuit for a gas discharge lamp, comprising:
- input terminals, which are to be connected to a main source of a substantial sinusoidal low frequency mains voltage;
- a rectifier circuit for receiving and rectifying the mains voltage to provide a rectified voltage;
- a first generator (4), which is a voltage to frequency controlled generator, for providing a substantial rectangular high frequency inverter control signal, a control input of the first generator receiving a modulating signal which modulates the frequency of the inverter control signal to provide a modulated inverter control signal;
- an inverter (2), which comprises switches, which are arranged to switch the rectified voltage and to output the switched rectified voltage as an inverter output voltage, the inverter being controlled by the modulated inverter control signal to control the frequency of the inverter output voltage to the frequency of the modulated inverter control signal;
- a tank circuit, which is connected to the inverter and to the lamp to supply the inverter output voltage to the lamp;
- characterized by
- a first control loop which comprises:
- a first measuring circuit for measuring a current which is representative for an input current supplied by the main source to provide a current measurement signal (im);
- a second generator (10) for generating a reference waveform signal with a frequency of and being synchronized with a supply voltage which corresponds to the measured current
- a first subtractor (8) for subtracting the current measurement signal from the reference waveform signal to provide a first error signal;
- and
- a first control circuit (6) which is arranged for receiving the first error signal and for providing the modulating signal;
- whereby the first control loop is arranged to minimize the first error signal.
Dependencies are inferred from the claim text.