Low watt metal halide lamp apparatus
AssigneeWelch Allyn, Inc.
InventorRobert J. Wood
Life of this patent
Estimating the term…
Abstract
A low DC input, low wattage, high efficacy metal halide arc discharge lamp apparatus is provided which has a simplified control system including a regulated power supply, a forty kilohertz oscillator and driver for powering the bulb a main power transformer connected to the metal halide bulb; a starting and filtering inductive/capacitive network connected to the secondary of said main power transformer for start up and running the arc discharge bulb, and a power output sensing and emergency shutdown control circuit for safety shutdown of the system should a failure occur in the lamp or associated circuitry that could cause undesired sparking. An automatic mechanism for compensating for aging of the discharge bulb is also provided.
Claims19
A high efficacy low watt metal halide arc discharge apparatus having a lamp and a ballast control circuit comprising in combination:
- a metal halide arc discharge lamp having a low power output;
- a dc power source sufficient to operate said arc discharge lamp at a desired power level;
- means for regulating the output voltage of said DC power source to a predetermined value;
- a transformer having a primary and a secondary winding;
- said transformer being wound to have the characteristics that the output voltage of the transformer is inversely proportional to the output current of the transformer, and the lower output of the transformer is substantially constant when the secondary is connected to a varying resistive load;
- an oscillator circuit switchably connected to said transformer primary winding to provide lamp operating power to said transformer;
- switching means connecting and disconnecting said oscillating circuit to said transformer primary winding to limit the power input to said transformer;
- said transformer secondary winding being connected to said arc discharge lamp;
- a rectifier connected in series with said arc discharge lamp and the transformer secondary to convert the oscillator output to a pulsed DC lamp operating power;
- and
- a starting and filtering inductive/capacitive network connected to said transformer secondary and said discharge lamp for both generating a high starting voltage and smoothing said pulsed DC operating power, said network being coupled to said lamp and supplying smooth DC operating power thereto;
- so that said lamp can be started and operated at rated light output while automatically compensating for changing lamp resistance.
A low DC voltage input ballast for operating a metal halide arc discharge lamp which comprises:
- a DC power source sufficient to operate an arc discharge lamp at a desired power level;
- means for regulating the output voltage of said DC power source to a predetermined value;
- an oscillator having an operating frequency between 30-50 kilo hertz for providing a source of AC operating power to the lamp to be operated;
- driver means connected to said oscillator for limting the AC power oscillator operation to a 40%-60% duty cycle;
- a transformer having a primary winding connected to said driver means and a secondary winding connected to the lamp to be operated, said transformer being wound to provide substantially constant power to the lamp when the internal resistance of the lamp changes;
- rectifying means connected to the secondary of said transformer for converting said oscillator AC operating power to a pulsed DC operating power;
- a starting and filtering inductive/capacitive network connected to the secondary of said transformer for generating a high starting voltage and smoothing said pulsed DC operating power;
- power output sensing means connected to said transformer secondary winding;
- comparator means connected to said power output sensing means for determining when said transformer secondary winding power output exceeds a predetermined limit;
- and
- alarm and emergency shutdown circuitry connected to said comparator means for actuating an indicating means when a first power output level is sensed and shutting down said oscillator when a second higher power output level is sensed.
The method of controlling and operating a low power metal halide are discharge lamp which comprises:
- providing a source of DC power sufficient to operate the arc discharge lamp;
- regulating the voltage output of said source of DC power to a predetermined value;
- providing an oscillator, having a two digit kilohertz frequency, to furnish operating power to the lamp;
- controlling the duty cycle of said oscillator to a predetermined amount so as to apply the desired operating power to the lamp;
- providing a transformer for converting said oscillator voltage and current to desired levels for energizing the lamp, said transformer being wound to have the characteristic that a constant power output is provided to the lamp when internal resistance of the lamp varies;
- connecting the arc discharge lamp to the transformer output;
- rectifying and smoothing said oscillator operating power in said transformer output to apply DC power to the lamp;
- and
- providing a high voltage pulse generating means coupled to the output of said transformer for selectively applying a striking pulse to the arc discharge lamp.
A low power metal halide arc discharge apparatus of the type having a lamp and ballast control circuit, comprising:
- a low wattage metal halide arc discharge lamp;
- a regulated low voltage directed current power source;
- and
- oscillator-driver means connected to said power source for providing a voltage at a predetermined frequency to a duty cycle regulator that delivers power at said predetermined frequency and at a predetermined duty cycle to a switchless self-compensating circuit means for delivering smooth direct current to said lamp at a substantially constant power level when said lamp is operating;
- said switchless means comprising a transformer coupled to said lamp;
- whereby a stable light output is produced when internal resistance of the lamp changes as the lamp ages.
Dependencies are inferred from the claim text.