Methods and protection schemes for driving discharge lamps in large panel applications
AssigneeMonolithic Power Systems, Inc.
InventorsWei Chen, James Moyer, Paul Ueunten
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Abstract
The present disclosure introduces a simple method and apparatus for converting DC power to AC power for driving discharge lamps such as a cold cathode fluorescent lamp (CCFL), an external electrode fluorescent lamp (EEFL), or a flat fluorescent lamp (FFL). Among other advantages, the invention allows the proper protection under short circuit conditions for applications where the normal lamp current is greater than safe current limit.
Claims14
A method of short circuit protection in a driver apparatus, the driver apparatus driving a lamp load through a transformer, the method comprising:
- monitoring a feedback voltage on a load side of said transformer;
- if said feedback voltage is higher than a preset threshold, continuing normal operation;
- and
- if said feedback voltage is lower than a preset threshold, limiting a current supplied by said driver apparatus to a safe current ISAFE.
A method of short circuit protection in a driver apparatus, the driver apparatus driving a lamp load through a transformer, the method comprising:
- monitoring a feedback voltage on a load side of said transformer;
- determining the root mean square of said feedback voltage;
- limiting a current supplied by said driver apparatus to the minimum of either a brightness current limit or the root mean square of said feedback voltage divided by a threshold impedance RTH.
An apparatus for driving a lamp load through a transformer comprising:
- means for monitoring a feedback voltage on a load side of said transformer;
- comparator means for determining if said feedback voltage is higher than a preset threshold, and
- (1) if so, continuing normal operation;
- and
- (2) if not, limiting a current supplied by said apparatus to a safe current ISAFE.
Dependencies are inferred from the claim text.