Variable high frequency ballast circuit
AssigneeNorth American Philips Corporation
InventorsEdward H. Stupp, Mark W. Fellows
Life of this patent
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Abstract
A variable high-frequency ballast circuit for igniting and operating energy saver discharge lamps includes a high frequency inverter that energizes the lamps with a given high frequency voltage at which reliable lamp ignition is assured. The lamp current is monitored so as to automatically increase the lamp operating frequency to an optimum value as soon as the lamps ignite.
Claims19
A circuit for starting and ballasting at least one gas discharge lamp of the type exhibiting a poor starting characteristic at a desired high operating frequency for the lamp and with a given lamp energization voltage comprising,
- an inverter circuit including first and second switching transistors each having a control electrode,
- a reactive ballast impedance coupling an output terminal of the inverter circuit to said discharge lamp,
- means for sensing the flow of current through said discharge lamp and for deriving a control signal determined thereby and indicative of the condition of the lamp,
- a variable frequency drive circuit for deriving an output signal whose frequency is determined by the value of an input signal applied to a control input thereof,
- means coupling said control signal to the control input of the variable frequency drive circuit,
- second means coupling said output signal of the variable frequency drive circuit to the control electrodes of said first and second switching transistors to control the conduction thereof so that the transistors conduct in mutually exclusive time intervals, and
- means for adjusting the frequency of said variable frequency drive circuit to a predetermined frequency value when said sensing means indicates that the lamp is in an unlit condition and for automatically increasing the frequency thereof to the desired operating frequency when the sensing means derives a control signal indicating that the lamp is in its operating condition, said frequency value being chosen to be above 60 Hz and below the desired high operating frequency of the discharge lamp and being of a frequency such that said given energization voltage provides reliable ignition of the discharge lamp.
A control apparatus for energizing a gas discharge lamp of the type requiring a high ignition voltage in a desired high frequency operating range of the lamp and which, at a predetermined high frequency below the minimum operating frequency in said desired high frequency range and above 60 Hz, requires a lower ignition voltage to ensure reliable ignition of the discharge lamp, said control apparatus comprising:
- a driven inverter circuit including first and second switching transistors and input switching control means,
- a reactive ballast impedance coupling an alternating voltage developed in the inverter circuit to said discharge lamp,
- means for sensing lamp current,
- a variable frequency drive circuit coupled between the sensing means and the inverter circuit input control means for deriving a variable frequency control signal whose frequency is determined by the lamp current sensed and which signal controls the inverter circuit switching frequency, and
- means controlled by the sensing means for adjusting the frequency of the variable frequency drive circuit to said predetermined high frequency before ignition of the lamp whereby application of said lower ignition voltage to the discharge lamp by the inverter circuit ignites the lamp,
- said sensing means being responsive to the lamp current after lamp ignition to cause the variable frequency drive circuit to increase the frequency of said variable frequency control signal to said desired high frequency operating range.
A control circuit for energizing at least one gas discharge lamp of the type exhibiting an unreliable starting charateristic at a desired high operating frequency and at a given lamp energization voltage comprising:
- a inverter circuit including first and second switching transistors,
- a non-resonant coupling network including a reactive ballast impedance coupling an output of the inverter circuit to said discharge lamp,
- means for deriving a control signal determined by the discharge condition of the lamp,
- a variable frequency drive circuit having an output coupled to a control input of the inverter circuit and responsive to said control signal for developing an output signal whose frequency is determined by the control signal, and wherein
- said control signal deriving means controls the frequency of said variable frequency drive circuit to a predetermined frequency value when the lamp is in a pre-ignition state whereby said given energization voltage is now sufficient to initiate a lamp discharge, said predetermined frequency value being chosen to be above 60 Hz and below the desired high operating frequency of the discharge lamp.
Dependencies are inferred from the claim text.