L6563S View Datasheet(PDF) - STMicroelectronics
Part Name
Description
MFG CO.
'L6563S' PDF : 43 Pages View PDF
L6563S
Application information
6.4
THD optimizer circuit
The L6563S 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 will result in both minimizing the time interval where energy transfer is lacking and fully
discharging the high-frequency filter capacitor after the bridge.
Figure 38 shows the internal block diagram of the THD optimizer circuit.
Figure 38. THD optimizer circuit
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Doc ID 16116 Rev 4
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