This application is a continuation of co-pending, commonly-assigned U.S. patent application Ser. No. 11/483,374, filed Jul. 7, 2006, entitled ELECTRONIC BALLAST HAVING A FLYBACK CAT-EAR POWER SUPPLY, the entire disclosure of which is hereby incorporated by reference.
Electronic ballasts for fluorescent lamps typically include a "front end" and a "back end". The front end typically includes a rectifier for changing alternating-current (AC) mains line voltage to a direct-current (DC) bus voltage and a filter circuit for filtering the DC bus voltage. The ballast back end typically includes a switching Beats Studio boutique inverter for converting the DC bus voltage to a high-frequency AC voltage, and a resonant tank circuit having a relatively high output impedance for coupling the high-frequency AC voltage to the lamp electrodes.
The front end of electronic ballasts also often include a boost converter, which is an active circuit for boosting the magnitude of the DC bus voltage above peak of line voltage, and for improving the total harmonic distortion (THD) and power factor of the input current to the ballast. However, boost converters typically include integrated circuits (IC) and semiconductor switches, such as field effect transistors (FETs). In order to handle the amount of current required to drive the lamp at high end (i.e. at or near 100% light intensity), the components of such a boost converter are typically large and costly.
The ballast 100 includes an electromagnetic interference (EMI) filter 115 and a rectifier 120 both capable of being connected to an AC power supply such as a typical 120V, 60 Hz AC main. The EMI filter 115 isolates high-frequency noise generated by the ballast circuitry from the AC power supply. The rectifier 120 converts the AC input voltage to a rectified pulsating DC voltage Casque Beats pas cher 210, which has a maximum value of VPEAK (shown as 230 in FIG. 2a). For example, if the AC input voltage has an RMS (root mean square) value of 277V, the value of VPEAK will be approximately 392V. The rectifier 120 is connected to a valley-fill circuit 130 through a diode 140. A high-frequency filter capacitor 150 is connected across the inputs to the valley-fill circuit 130. The valley-fill circuit 130 selectively charges and discharges an energy-storage device, such as one or more capacitors, so as to fill the "valleys" between successive rectified voltage peaks to produce a substantially DC bus voltage 220. The DC bus voltage is the greater of either the rectified voltage, or the voltage across the energy storage device in the valley-fill circuit 130.
According to an embodiment of the present invention, an electronic ballast, which draws an input current from an AC power supply and drives a gas discharge lamp, comprises: (1) a rectifier for rectifying an AC input voltage from said AC power supply to produce a rectified voltage; (2) a filter circuit for converting said rectified voltage to a filtered bus voltage; (3) an inverter for converting said bus voltage to a high-frequency AC drive voltage to drive said lamp; (4) a control circuit coupled to the inverter for controlling the operation of said inverter; and (5) a ballast power supply that receives said rectified voltage and generates a substantially DC voltage for powering said control circuit. The ballast power supply selectively draws current from said AC power supply when said rectified voltage is lower than a predetermined value such that said input current to said ballast is essentially sinusoidal. The ballast power supply is coupled to said inverter and is operable to provide current to said inverter when the magnitude of said rectified voltage is less than said predetermined level.
According to another embodiment of the present invention, an electronic ballast for driving a gas discharge lamp comprises a rectifier, an inverter, a first circuit coupled from the rectifier to the inverter, and a second coupled from the Beats Studio boutique rectifier to the inverter in parallel electrical connection with the first circuit. The rectifier rectifies the AC input voltage from said AC power supply to produce a rectified voltage, while the inverter generates a high-frequency AC drive voltage to drive said lamp. The first circuit supplies current from said AC power supply to said inverter and provides Casque Beats pas cher said rectified voltage to said inverter when the magnitude of said rectified voltage is greater than a predetermined value. The second circuit supplies current to said inverter and provides a boosted voltage to said inverter when the magnitude of said rectified voltage is less than said predetermined value. The magnitude of said boosted voltage is greater than the magnitude of said rectified voltage when the magnitude of said rectified voltage is less than said predetermined value.
According to another aspect of the present invention, an electronic ballast for driving a gas discharge lamp comprises a rectifier for rectifying an AC line voltage to produce a rectified voltage, Beats By Dre Pas Cher and a boost converter for receiving said rectified voltage and producing a substantially DC output voltage having an average magnitude less than a peak value of said rectified voltage.
A cat-ear circuit for an electronic ballast having a front end for receiving an AC input voltage and a back end for driving a gas discharge lamp is also described herein. The cat-ear circuit comprises an input for receipt of a rectified voltage, a semiconductor switch, a transformer, a control circuit, and first and second outputs. The semiconductor switch is coupled in series electrical connection between said input and a circuit common and has a conductive state and a non-conductive state. The transformer has a primary winding and a secondary winding, where said primary winding coupled in series electrical connection with said semiconductor switch. The control circuit is operable to receive said rectified voltage and to repeatedly switch said semiconductor switch at a high frequency between said conductive state and said non-conductive state only when said rectified voltage is below a predetermined level, such that a boosted voltage is produced across said secondary winding of said transformer. The first output for provides said boosted voltage to said ballast back end only when said rectified voltage is below said predetermined level, and Casque Beats by dre the second output provides a substantially low-magnitude DC voltage.
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