L6699

Operation at no load or very light load

Doc ID 022835 Rev 2

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Figure 17.

How the L6699 can switch off a PFC controller at light load

To help the user meet energy saving requirements even in power-factor-corrected systems,

where a PFC pre-regulator precedes the DC-DC converter, the L6699 allows that the PFC

pre-regulator can be turned off during burst-mode operation, therefore eliminating the no

load consumption of this stage (0.5

EMC regulations on low-frequency harmonic emissions refer to nominal load, no limit is

envisaged when the converter operates with light or no load.

To do so, the L6699 provides pin 8 (PFC_STOP): it is an open drain output, normally open,

that is asserted low when the IC is idle during burst-mode operation. This signal is externally

used for switching off the PFC controller and the pre-regulator as shown in

Figure 17. When

the L6699 is in UVLO the pin is kept open to allow the PFC controller to start first.

The PFC_STOP pin is also used by some protection functions (OCP, OLP and latched

shutdown). Please refer to the relevant sections for more information.

AM11388v1

L6699

PFC_STOP

9

L6563S/H

L6564, L6564T/H

L4984

PFC_OK

(AC_OK)

L6699

PFC_STOP

9

L6562/2A

12

Vcc

ZCD (L6562)

INV (L6562A)

BC547

BC547