| 摘要 |
An electronic ballast for a gas discharge lamp, preferably a fluorescent lamp, has a d.c. source connected to a load circuit that includes a series resonance circuit and a lamp by an inverter that has a high side switch Q1 and a low side switch Q2 in a half bridge arrangement. The switches are alternately controlled with a delay time or dead time after one of the switches is switched off and before the other is switched on. The dead time is varied by controller 1 depending on detection of a negative current in a body diode D2 of the low side switch Q2. The dead time can be varied between a fixed value (fig 4, TD) and a maximum value, being set at the fixed value if the time between the high side switch turning off and detection of negative current in the low side switch is less than a first duration; and ended if the time period is less than a second duration. Switching of both switches can be suspended if negative current in the body diode is not detected within a time limit. Switching of the high side switch Q1 can be suspended in response to detecting a negative current in the body diode of the low side switch Q2 during the dead time after the low side switch is turned off. The current in the low side diode D2 can be monitored by detecting a voltage across a shunt resistor R1 at the foot of the bridge |
