April 2011
Intermediate to advanced
248 pages
5h 19m
English
Content preview from Power Supplies for LED Driving
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CHAPTER 8 LED Drivers with Power Factor Correction
8.1 Power Factor Correction
Power factor correction, or PFC, is a term used with AC mains powered circuits. A good power factor is when the AC current is in phase with the AC voltage. A pure resistive load has a power factor of 1, but active loads tend to have power factors closer to 0.5, unless special measures are taken to ‘correct’ this.
The most common power factor correction circuit is a boost converter. The AC line voltage is boosted to about 400V and the amplitude of the current pulses into a storage capacitor is arranged to be sinusoidal. This is achieved by switching the current on for short but constant periods: as the supply voltage rises and falls, so does the amplitude of the current. ...
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