Test results and significant waveforms

AN3063

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Doc ID 16261 Rev 3

ripple at twice the mains frequency that will cause distortion of the current reference

(resulting in high THD and poor PF). If it is too large, there will be a considerable delay in

setting the right amount of feed-forward, resulting in excessive overshoot and undershoot of

the pre-regulator's output voltage in response to large line voltage changes. Clearly a trade-

off was required.

The L6563H implements an innovative voltage feed-forward which, with a technique that

overcomes this time constant trade-off issue whichever voltage change (both surges and

voltage equal to the peak of the rectified sine wave applied on pin MULT (pin #3). In this way,

internal diode. In case of line voltage drop, an internal "mains drop" detector enables a low

reaching the new voltage level. Consequently, an acceptably low steady-state ripple and low

current distortion can be achieved without any considerable undershoot or overshoot on the

preregulator's output like in systems with no feed-forward compensation.

In

Figure 19 we find the behavior of the EVL6563H-100W demonstration board in case of an

for the stability of the output voltage which is not affected by the input voltage surge. In fact,

the output voltage remains stable at its nominal value. The opposite is confirmed in

Figure 18 where the behavior of a PFC using the L6562A and delivering same output power

is shown. The controller cannot compensate a mains surge and the output voltage stability

is guaranteed by the feedback loop only. Unfortunately, as previously stated, its bandwidth is

narrow and thus the output voltage has a significant deviation from the nominal value. The

circuit has the same behavior in case of a mains surge at any input voltage, and it is also not

affected if the input mains surge happens at any point along the input sine wave.

Figure 18.

L6562A input mains surge 90 Vac to

Figure 19.

EVL6563H-100W TM PFC: input

mains surge 90 Vac to 140 Vac

CH1: Vout

CH2: MULT (pin #3)

CH4: I_AC

CH1: Vout

CH2: MULT (pin #3)

CH4: I_AC