Patent ID: 6914395

Claim:
An electronic ballast for a high intensity discharge (HID) lamp, said ballast comprising: a power converter configured to convert an input DC voltage into a ballast output power for driving said HID lamp; a controller configured to control said power converter to vary said ballast output power being supplied to said HID lamp; and a lamp vower switch configured to monitor a lamp output parameter that said HID lamp exhibits after it starts discharging, discriminate a rated lamp power of said HID lamp based upon said monitored lamp output parameter, and provide a lamp power signal indicative of the discriminated rated lamp power. said lamp power switch comprising: a monitor configured to keep monitoring said lamp output parameter before said HID lamp comes into a stable lamp operating condition; a timer configured to start counting a time when said HID lamp starts discharging, and output an enabling signal when said counted time exceeds a predetermined time; and a lamp discriminator configured to compare said lamp output parameter with a predetermined reference value upon receiving said enabling signal, and provide said lamp power signal when said lamp output parameter satisfies a predetermined criteria; and said controller being configured to vary said ballast output power to match with said rated lamp power of said HID lamp according to said lamp power signal received.