Lamp controller with lamp status detection and safety circuitry

• US 5,751,115 A
• Filed: 12/03/1996
• Issued: 05/12/1998
• Est. Priority Date: 03/31/1995
• Status: Expired due to Term

• Current Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Original Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Inventors: Leyton, Paul, Venkitasubrahmanian, Sreeraman, Xia, Yongping, Jayaraman, Raj
• Primary Examiner(s): Pascal, Robert
• Assistant Examiner(s): Kinkead, Arnold
• Application Number:
  US08/759,350
• Time in Patent Office: 525 Days
• Field of Search: 315/225, 315/119, 315/307, 315/DIG. 5, 315/107, 315/106, 315/277, 363/49, 363/50, 363/56, 307/157
• US Class Current: 315/225
• CPC Class Codes: H05B 41/2828 using control circuits for the switching elements H05B41/2827 takes precedence
• CPC Class Codes: H05B 41/2981 for protecting the circuit against abnormal operating conditions
• CPC Class Codes: H05B 41/3925 by frequency variation H05B41/3922 takes precedence
• CPC Class Codes: Y02B 20/00 Energy efficient lighting technologies, e.g. halogen lamps or gas discharge lamps
• CPC Class Codes: Y10S 315/05 Starting and operating circuit for fluorescent lamp

Abstract

A ballast includes safety circuitry which senses lamp status through various phases of ballast operation. According to one feature, the ballast is prevented from supplying an output voltage upon initial energization of the ballast when a lamp is not present at the output terminals. The presence of a filament is sensed via a DC path extending through the filament heater windings of an output transformer. When the DC path is not complete, a control input, for example the power supply input of the ballast controller, is not provided with a voltage to start ballast operation. The DC path is also used to restart the ballast if a defective lamp is replaced with a good one. Over-voltage and capacitive mode detection is also disclosed to shut down ballast output upon lamp failure/removal.

Claims

1. A ballast for a gas discharge lamp having at least one electrode extending and defining an electrically conductive path between a pair of lamp contacts, said ballast comprising:

a) input means for receiving a source of electrical energy to power said ballast;

b) ballast means, connected to said input means, for controlling the electrical power supplied to said gas discharge lamp, said ballast means including an isolation transformer coupled to and for electrically isolating a pair of output terminals for connection to the pair of lamp contacts of the gas discharge lamp; and

c) safety means including means for detecting the presence of a conductive path between said output terminals, to thereby confirm the presence of the discharge lamp and the continuity of the at least one electrode between the lamp contacts, upon initial application of electrical energy to said input means, said detecting means being coupled to said ballast means such that said ballast means does not energize said gas discharge lamp and provides no electrical potential at said output terminals in the absence of a conductive path between said output terminals upon initial application of electrical energy to said input means.

2. A ballast according to claim 1, wherein said ballast means includes an inverter which oscillates to energize said gas discharge lamp, and said safety means includes means for preventing said inverter from oscillating until there exists a conductive path between said output terminals.

3. A ballast according to claim 2, wherein said input means is receptive of an AC mains voltage and further comprising:

a power supply stage providing a DC voltage to said inverter with a magnitude substantially higher than the peak of the AC mains voltage supplied at said input means, said power supply stage being coupled to said inverter so that said power supply stage is inoperative whenever the inverter is not oscillating.