| 摘要 |
The ballast has a self-oscillating half-bridge inverter with alternately conductive MOSFET's V1, V2 having respective functionally independent control circuits which have no data transmission link therebetween. Each MOSFET V1 or V2 is turned on when a certain voltage prevails thereacross, and is turned off by a respective transistor V3 or V4 which turns on when the current through the respective MOSFET V1 or V2 and current sensing resistor R1 or R2 rises to a predetermined threshold level. As the MOSFET V1 or V2 turns off its drain voltage rises, whereby V3 or V4 receives more base current via C1 or C2; this positive feedback results in rapid turn off of V1 or V2. The turn-off threshold current level and the turn-on voltage level can be adjusted by adjusting a control voltage Uohj, thereby varying the power of lamp DL. During lamp starting, a secondary winding Lt of an inductor Le, in series with the lamp DL, is short-circuited by a switch V9, V10 so that the inverter then operates at a higher frequency. <IMAGE>
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