Lamp protection circuit for electronic ballasts
AssigneeMagneTek, Inc.
InventorBryce L. Hesterman
Life of this patent
Estimating the term…
Abstract
An electronic ballast has a protection circuit particularly useful for smaller diameter gas discharge lamps including compact fluorescent lamps. The protection circuit prevents lamps from overheating by preventing the ballast from providing sustained output power when the magnitude of the ballast output voltage indicates abnormal lamp operation. The protection circuit has a voltage sensor which develops a voltage that is more negative than the negative DC supply terminal of the inverter so that an inexpensive low-voltage SCR can be used to turn off the inverter. The circuit provides automatic restarting of the ballast after a new lamp has been installed to eliminate the need for toggling the input power to the ballast.
Claims20
An electronic ballast for powering at least one gas discharge lamp comprising:
- an inverter having a resonant inductor, a switching transistor, a plurality of output terminals, and an output voltage, the switching transistor having a common terminal and a control terminal, the common terminal coupled to a negative DC supply terminal;
- voltage sensing means for providing at a voltage-sensor output terminal a DC sense voltage having a magnitude that is directly related to the magnitude of the inverter output voltage, and negative in polarity with respect to the negative DC supply terminal, the voltage sensing means including a delay capacitor connected between the negative DC supply terminal and the voltage-sensor output terminal for delaying the response of the DC sense voltage to changes in the inverter output voltage;
- and
- trigger means for providing a negative pulse to shut off the inverter by discharging the delay capacitor into the control terminal of the switching transistor when the magnitude of the DC sense voltage exceeds a threshold level, thereby preventing the ballast from providing sustained output power when the magnitude of the inverter output voltage indicates abnormal lamp operation.
An electronic ballast for powering at least one gas discharge lamp comprising:
- a power supply having a positive DC supply terminal and a negative DC supply terminal;
- an inverter having a resonant inductor, a switching transistor, a plurality of output terminals, and an output voltage, the switching transistor having a common terminal and a control terminal, the common terminal coupled to the negative DC supply terminal;
- starting means for providing at least one starting pulse to the control terminal of the switching transistor, the starting means receiving a starting current through a starting current source;
- inhibit means having an inhibit control terminal and operative to disable the starting means by shunting the starting current away from the starting means after a delay period following receipt of an inhibit signal at the inhibit control terminal;
- voltage sensing means for providing at a voltage-sensor output terminal a DC sense voltage having a magnitude that is directly related to the magnitude of inverter output voltage and negative in polarity with respect to the negative DC supply terminal, the voltage sensing means including a delay capacitor connected between the negative DC supply terminal and the voltage-sensor output terminal for delaying the response of the DC sense voltage to changes in the inverter output voltage;
- and
- trigger means for providing a negative pulse to shut off the inverter by discharging the delay capacitor into the control terminal of the switching transistor when the magnitude of the DC sense voltage exceeds a threshold level, thereby preventing the ballast from providing sustained output power when the magnitude of the inverter output voltage indicates abnormal lamp operation.
A method of operating at least one gas-discharge lamp connected to an electronic ballast, comprising the steps of:
- (a) starting an inverter with a starting means;
- (b) providing from the inverter a current-limited output voltage for operating at least one gas-discharge lamp from a plurality of output terminals, the inverter having a switching transistor, the switching transistor having a common terminal and a control terminal, the common terminal coupled to a negative DC supply terminal;
- (c) developing a DC sense voltage across a delay capacitor, the DC sense voltage having a magnitude that, after a time delay, is directly related to the magnitude of the inverter output voltage, and the negative in polarity with respect to the negative DC supply terminal;
- and
- (d) shutting off the inverter by discharging the delay capacitor into the control terminal of the switching transistor when the magnitude of the DC sense voltage exceeds a threshold level, thereby preventing the ballast from providing sustained output power when the magnitude of the inverter output voltage indicates abnormal lamp operation.
Dependencies are inferred from the claim text.