Electronic ballast having emitter coupled transistors and bias circuit between secondary winding and the emitters

• US 4,469,988 A
• Filed: 06/23/1980
• Issued: 09/04/1984
• Est. Priority Date: 06/23/1980
• Status: Expired due to Term

• Current Assignee: Donald L. Cronin
• Original Assignee: Donald L. Cronin
• Inventors: Cronin, Donald L.
• Primary Examiner(s): Chatmon, Saxfield
• Application Number:
  US06/161,759
• Time in Patent Office: 1,534 Days
• Field of Search: 315/DIG. 7, 315/DIG. 5, 315/205, 315/209, 315/DIG. 2, 315/232, 315/185, 331/113 A
• US Class Current: 315/209.00R
• CPC Class Codes: H05B 41/295 with semiconductor devices and specially adapted for lamps with preheating electrodes, e.g. for fluorescent lamps
• CPC Class Codes: Y10S 315/02 High frequency starting operation for fluorescent lamp
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp

Abstract

An electronic ballast for energizing fluorescent lamps comprising a converter including a rectifier and a filter for converting an alternating source voltage into a direct current voltage, a network including first and second switching transistors, a tank circuit having a primary winding of a transformer, a secondary winding of the transformer for providing feedback of a portion of the voltage developed across the tank circuits and a bias circuit coupled between the opposite ends of the secondary winding and the emitters of the transistor for alternatively applying bias to the transistors, the network serving to convert a direct current voltage into an amplified sinusoidal voltage having a high frequency, and fluorescent lamps connected in a series configuration coupled across the primary winding.

Claims

1. An electrical ballast for energizing fluorescent lamps comprising:

first means for converting an alternating source voltage into a substantially direct current voltage;

second means for converting a direct current voltage into an amplified sinusoidal voltage having a relatively high frequency that is generally inaudible to humans, said second means including

first and second power transistors, each having a collector, a base and an emitter, said emitters being coupled together;

a tank circuit including a primary winding of a transformer connected to said collectors, said tank circuit being resonant at said relatively high frequency;

a secondary winding of the transformer having its opposite ends connected to said bases and being inductively coupled to said primary winding, said secondary winding serving to feed back a portion of the voltage developed by said tank circuit; and

bias circuit means coupled between the opposite ends of the secondary winding and said emitters, said secondary winding and said bias circuit means serving to alternatively bias the base-emitter junction of said first and second transistors with a substantial portion of the feedback voltage developed across said secondary winding, whereby when said direct current voltage is connected across said base and said emitter of said first transistor, said amplified sinusoidal voltage is developed across said primary winding;

at least two fluorescent lamps connected in a series configuration across said primary winding; and

capacitive means having a relatively high capacitive reactance at the frequency of the alternating source voltage for isolating said fluorescent lamps from said second means for converting such that should said lamps be inadvertently connected to ground, electrical stress will not be transmitted to said second means for converting.

2. An electronic ballast as recited in claim 1 and further including capacitive means for selectively changing the current flowing through said lamps whereby the intensity of the light produced by said lamps is capable of being adjusted.

3. An electronic ballast as recited in claim 1 wherein said lamps include a heater element means and wherein said first means includes an inductive means, said heater element means being inductively coupled to said inductive means and serving to load said inductive means so as to limit transient voltages from being coupled to said first means.

4. An electrical ballast as recited in claim 1 wherein said bias circuit means includes a pair of blocking diodes having their cathodes connected to the opposed ends of said secondary winding and their anodes connected together, and an inductor having one end connected to the anodes and having its other end coupled to said emitters, said bias circuit serving to drive said bases with a generally pulse shaped voltage.

5. An electrical ballast for energizing fluorescent lamps comprising:

first means for converting an alternating source voltage into a substantially direct current voltage; and

second means for converting a direct current voltage into an amplified sinusoidal voltage having a relatively high frequency that is generally inaudible to humans, said second means including

first and second power transistors, each having a collector, a base and an emitter, said emitters being coupled together;

a tank circuit including a primary winding of a transformer connected to said collectors, said tank circuit being resonant at said relatively high frequency;

a secondary winding of the transformer having its opposite ends connected to said bases and being inductively coupled to said primary winding, said secondary winding serving to feed back a position of the voltages developed by said tank circuit; and

bias circuit means including a pair of blocking diodes having their cathodes connected to the opposed ends of said secondary winding and their anodes connected together, and an inductor having one end connected to the anodes and having its other end coupled to said emitters, said bias circuit serving to drive said bases with a generally pulse shaped voltage, said secondary winding and said bias circuit means serving to alternatively bias the base-emitter junctions of said first and second transistors with a substantial portion of the feedback voltage developed across said secondary winding, whereby when said direct current voltage is connected across said base and said emitter of said first transistor, said amplified sinusoidal voltage is developed across said primary winding and applied to energize the fluorescent lamps.

6. An electronic ballast as recited in claim 5 and further including fluorescent lamps connected to said primary winding and capacitive means for selectively changing the current flowing through the fluorescent lamps whereby the intensity of the light produced by said lamps is capable of being adjusted.

7. An electronic ballast as recited in claim 5 and further including fluorescent lamps having a heater element, and wherein said first means includes an inductive means, said heater element being inductively coupled to said inductive means and serving to load said inductive means so as to limit transient voltages from being coupled to said first means.