Voltage-controlled ballast for gas-discharge lamps
AssigneeVossloh-Schwabe Elektronik GmbH
InventorsGert Knobloch, Peter Haaf
Life of this patent
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Abstract
An electronic, externally controlled ballast has a control oscillator which feeds a fluorescent lamp via an invertor bridge and a resonant circuit. To keep the voltage constant, there are derived from the lamp AC voltage charge packets whose size (and/or phase angle) characterizes the size of the lamp AC voltage. The charge packets are conducted onto a frequency-determining capacitor of the oscillator, which is designed as a sweep oscillator, voltage control thereby being achieved. The ballast provides for reliable operation of gas-discharge lamps. Its design is robust and yet simple, avoids undesired hunting and delivers a good degree of voltage stability.
Claims21
A ballast for a gas-discharge lamp comprising:
- a frequency-determining oscillator circuit comprising a capacitor whose charge increases and decreases in an alternating fashion between a maximum value and a minimum value in time with the oscillation frequency of the oscillator circuit;
- an invertor circuit which converts a provided DC voltage at the frequency prescribed by the oscillator circuit into an AC voltage which is present at its output and to which a series resonant circuit for feeding the gas-discharge lamp is connected;
- and
- a charge injector circuit which has an injector current path from the gas-discharge lamp to the capacitor over which charge packets are conducted onto the capacitor at a frequency synchronized with the capacitor AC voltage, the size and/or phase angle of which packets are/is a function of the voltage present at the gas-discharge lamp and/or the current flowing through it;
- wherein the capacitor is connected to a recharging path over which the capacitor is charged or discharged while the oscillator circuit is in its respective astable state and wherein said recharging path is a resistive current path with a positive feedback characteristic.
An electronic ballast for a gas-discharge lamp, said ballast comprising:
- a control oscillator for generating a control signal to control the frequency of an AC voltage supplied to said gas-discharge lamp;
- an invertor, connected to said control oscillator, for converting a provided DC voltage to said AC voltage with a frequency determined by said control signal;
- a charge packet injector, connected to said control oscillator, for injecting charge packets to said control oscillator to affect said control signal and thereby affect the frequency of said AC voltage supplied to said gas-discharge lamp;
- wherein the control oscillator includes a capacitor that is connected to a recharging path over which the capacitor is charged or discharged while the control oscillator is in its respective astable state and wherein said recharging path is a resistive current path with a positive feedback characteristic.
Dependencies are inferred from the claim text.