L6564T STMicroelectronics, L6564T Datasheet - Page 22
L6564T
Manufacturer Part Number
L6564T
Description
10 pin transition-mode PFC controller for outdoor applications
Manufacturer
STMicroelectronics
Datasheet
1.L6564T.pdf
(33 pages)
Available stocks
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Part Number:
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Part Number:
L6564TDTR.
Manufacturer:
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Quantity:
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Application information
6.4
Figure 30. THD optimizer circuit
22/33
THD optimizer circuit
The L6564T is provided with a special circuit that reduces the conduction dead-angle
occurring to the AC input current near the zero-crossings of the line voltage (crossover
distortion). In this way the THD (total harmonic distortion) of the current is considerably
reduced.
A major cause of this distortion is the inability of the system to transfer energy effectively
when the instantaneous line voltage is very low. This effect is magnified by the high-
frequency filter capacitor placed after the bridge rectifier, which retains some residual
voltage that causes the diodes of the bridge rectifier to be reverse-biased and the input
current flow to temporarily stop.
To overcome this issue the device forces the PFC pre-regulator to process more energy
near the line voltage zero-crossings as compared to that commanded by the control loop.
This results in both minimizing the time interval where energy transfer is lacking and fully
discharging the high-frequency filter capacitor after the bridge.
Figure 30
shows the internal block diagram of the THD optimizer circuit.
Doc ID 022671 Rev 1
L6564T