| 摘要 |
<p>A gas discharge lamp 43 is connected to MOS-FET's 36, 37 of a half-bridge inverter circuit which has an inverter driving integrated circuit 31 connected to means for pulse width control of the MOS-FET's 36, 37 during both pre-heating of lamp filaments 41, 42 and for dimming of the lamp 43. For soft-starting, the inverter initially operates at a minimum pulse width during a pre-heating period determined by an RC circuit 16, 19. A first DC power supply 7, 8 initially provides a maximum of 5 volts to the supply terminal VCC of the driver IC31. A second DC power supply, including a transformer 45, 46, gradually increases the supply for IC31 to 15 volts, resulting in a transistor 20 being controlled so that the pulse width of the inverter gradually increases to a maximum value. Pulse width adjustment for lamp dimming is also effected by controlling transistor 20 by means of a control signal input 57, 58 coupled to the transistor 20 via an opto-coupler 56. Increasing the control signal increases the conductance of transistor 20, thereby reducing the pulse width and reducing lamp brightness. An over-current protection circuit senses lamp current by means of the transformer 45, 46, excess current causing an SCR 10 to latch a transistor 17 on, whereby the transistor 20 is also latched on.</p> |
