Datasheet

AN3119 Test results and significant waveforms

Doc ID 16849 Rev 2 17/32

It is also possible to see, comparing Figure 24 and Figure 25, that the input current of the

latter has a better shape and the 3

harmonic current distortion is not noticeable; this

demonstrates the benefits of the new voltage feed-forward circuit integrated into the

L6563S, allowing a fast response to mains disturbances but using a quite long V

time

constant, also providing very low THD and high PF at the same time, as confirmed by the

measurements below in Figure 24 and 25:

Another function offered by the L6563S is brown-out protection, which is basically a not-

latched shutdown function which must be activated when a mains under voltage condition is

detected. This abnormal condition may cause overheating of the primary power section due

to an excess of RMS current. Brown-out can also cause the PFC pre-regulator to work

open-loop and this could be dangerous to the PFC stage itself and the downstream

converter, should the input voltage return abruptly to its rated value. A further problem is the

spurious restarts which may occur during converter power-down and that cause the output

voltage of the converter not to decay to zero monotonically. For these reasons it is usually

preferable to shut down the device in the case of brown-out.

Brown-out function is done by sensing the input mains through an internal comparator

connected to RUN (pin #10), connected via a divider to V

(pin #5) which delivers a voltage

signal proportional to the input mains. The enable and disable thresholds at which the

L6563S starts or stops the operation can be adjusted modifying that divider ratio. For

additional information please see [2].

Figure 24. L6563 Input current at 100 Vac -

50Hz C

=0.47 µF, R

=390 kΩ

Figure 25. EVL6563S-250W TM PFC: input

current at 100 Vac -50 Hz C

=1 µF,

=1 MΩ

THD= 4.36%, 3rd harmonic=94.6 mA

CH2: MULT (pin #3)

CH3: V

(pin #5)

CH4: I_AC

THD= 2.94%, 3rd harmonic=30.5 mA

CH2: MULT (pin #3)

CH3: V

(pin #5)

CH4: I_AC