| 摘要 |
A triac controller includes a triac driver that provides a triac control signal suitable for connection to a gate terminal of a triac, such that, when in a power-on condition, the control signal carries at least a first firing pulse during each half period of the alternating current power supply. A soft start subcircuit and a zero crossing detector directs the triac driver to produce the first firing pulse at a first firing pulse delay time after the zero crossing time. During a soft start operation the first firing pulse delay time varies monotonically with each successive half period from an initial delay time to a final delay time. An auto-retriggering subcircuit causes the triac driver to produce a second firing pulse at a predetermined retriggering delay time from an end of the first firing pulse if the triac is not in an on conduction state after the end of the first firing pulse during a same half period. The auto-retriggering subcircuit causes the triac driver to produce retriggering firing pulses periodically for so long as the triac is not in the on conduction state during the same half period; however, it is inhibited from causing the triac driver to produce retriggering firing pulses during a predetermined retriggering mask period at an end of the same half period. The soft start subcircuit includes a table specifying a plurality of predetermined first firing pulse delay values. A set signal is used to determine an index into the table. The plurality of predetermined first firing delay values is monotonically organized with respect to the index into the table, and a programmable rate variable determines a rate of change of the first firing delay values during a soft start operation.
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