Power supply for microwave discharge light source
First Claim
1. A circuit system adapted to supply microwave energy to a microwave discharge light source apparatus including an electrodeless discharge bulb, comprising:
- first rectifier means, adapted to be coupled to an AC voltage source of a relatively low voltage and frequency, for outputting a rectified voltage of a relatively low voltage;
filter means, coupled to said first rectifier means, for smoothing said rectified voltage outputted from said first rectifier means, and for outputting a smoother rectified voltage;
inverter means, coupled to said filter means, for converting said smoothed rectified voltage outputted from said filter means to an AC voltage of a relatively high frequency having a waveform of alternating pulses, wherein the relative high frequency f, expressed in kilohertz, of the AC voltage outputted by said inverter means is not less than 1500 divided by a diameter D, expressed in millimeters, of said electrodeless discharge bulb of the microwave light source apparatus;
space="preserve" listing-type="equation">f≦
1500/D;
pulse width modulation control means for modulating a pulse width of said pulses of said AC voltage outputted from said inverter means;
a step-up transformer having a primary winding coupled to an output of said inverter means, a secondary winding of the step-up transformer outputting an AC voltage of said relative high frequency and of a relatively high voltage;
second rectifier means, coupled to said secondary winding of said step-up transformer, for rectifying said AC voltage of the relative high frequency and the relative high voltage outputted from said secondary winding to a rectified voltage of a relatively high voltage; and
a magnetron coupled to said second rectifier means, to be supplied with and operated by said rectified voltage of the relative high voltage outputted from said second rectifier means.
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Abstract
A power supply circuit for a magnetron adapted to supply microwave energy to an electrodeless discharge bulb is disclosed. The circuit includes a rectifier coupled across a commerical AC voltage source, a filter for smoothing the output of the rectifier, an inverter for converting the DC voltage supplied from the filter into a high frequency AC voltage, a step-up transformer for stepping up the high frequency AC voltage outputted from the inverter, and a rectifier which rectifies the high voltage AC output of the transformer into a unidirectional voltage which is supplied to the magnetron. The inverter switching is controlled by a pulse width modulation control circuit to maintain the magnetron output power at a predetermined level. According to one aspect, an inductance is provided in the circuit which supresses high frquency components in the current flowing through the windings of the transformer; according to another aspect, the inverter switching frequency (expressed in kHz) is set at a value not less than 1500/D, wherein D represents the diameter of the electrodeless bulb expressed in millimeters; according to still another aspect, the peak to the mean value ratio of the magnetron current is limited under 3.75 inclusive.
47 Citations
13 Claims
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1. A circuit system adapted to supply microwave energy to a microwave discharge light source apparatus including an electrodeless discharge bulb, comprising:
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first rectifier means, adapted to be coupled to an AC voltage source of a relatively low voltage and frequency, for outputting a rectified voltage of a relatively low voltage; filter means, coupled to said first rectifier means, for smoothing said rectified voltage outputted from said first rectifier means, and for outputting a smoother rectified voltage; inverter means, coupled to said filter means, for converting said smoothed rectified voltage outputted from said filter means to an AC voltage of a relatively high frequency having a waveform of alternating pulses, wherein the relative high frequency f, expressed in kilohertz, of the AC voltage outputted by said inverter means is not less than 1500 divided by a diameter D, expressed in millimeters, of said electrodeless discharge bulb of the microwave light source apparatus;
space="preserve" listing-type="equation">f≦
1500/D;pulse width modulation control means for modulating a pulse width of said pulses of said AC voltage outputted from said inverter means; a step-up transformer having a primary winding coupled to an output of said inverter means, a secondary winding of the step-up transformer outputting an AC voltage of said relative high frequency and of a relatively high voltage; second rectifier means, coupled to said secondary winding of said step-up transformer, for rectifying said AC voltage of the relative high frequency and the relative high voltage outputted from said secondary winding to a rectified voltage of a relatively high voltage; and a magnetron coupled to said second rectifier means, to be supplied with and operated by said rectified voltage of the relative high voltage outputted from said second rectifier means. - View Dependent Claims (2, 3, 4, 5, 6, 8, 9, 10, 11, 12, 13)
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7. A circuit system as claimed in 2, wherein said inductance means comprises a leakage inductance of said transformer.
Specification