Status: Drinking too much beer in Munich ;)
Join Date: Feb 2012
Location: I would rather not say
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1) Turn-on. Power is applied to the ballast and the controller commands maximum voltage from the boost converter. Within 30ms, the igniter is ready to fire the tube. 2) Ignition. One or more high-voltage pulses, at 20Hz repetition, are applied to the lamp to ignite the arc. If the arc is not struck after 20 pulses, a serious fault is assumed and the sequence is terminated. 3) Take-over. To maintain the arc but also conserve the electrodes, the controller regulates lamp power to 75W maximum at up to 12A. This high current surge lasts only about 300ms. During ignition and take-over, the H-bridge applies DC to the lamp so as not to "disturb" the arc. 4) Warm-up. The H-bridge performs one switching cycle, first applying a negative half cycle of 10ms duration, then a positive half cycle. Power input to the lamp is regulated to 75W at 2.6A maximum. 5) Run-up. The H-bridge begins switching symmetrically at about 400Hz. Until the lamp voltage reaches 50V, the controller regulates lamp power to 75W at 2.6A maximum. This takes about 6-12 seconds. During this time, lamp intensity rises to near its full rated output. 6) Steady state. Lamp power is regulated to 35W ±2W. Continuing regulation ensures that the light output remains constant, regardless of variations in battery and lamp voltages. Of interest is the need to power the lamp from AC rather than DC. Apparently, applying a symmetrical square wave (ie, average = 0V) prevents electrolysis and other life-shortening effects within the arc tube. A relatively low switching frequency (250Hz-10kHz) ensures circuit efficiency and avoids acoustic reson-ances that can occur at higher frequencies.
|cheap , chips , hid|
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