SSL8516BT datasheet(13/35 Pages) PHILIPS

13 / 35 page

SSL8516BT

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Product data sheet

Rev. 1 — 26 May 2015

13 of 35

NXP Semiconductors

SSL8516BT

Greenchip PFC and flyback controller

At high output power the converter switches to quasi-resonant mode. The next converter

stroke starts after demagnetization of the transformer and detection of the valley. In

quasi-resonant mode, switching losses are minimized. This minimization is achieved by

the converter only switching on when the voltage across the external MOSFET is at its

minimum (see Section 7.3.2).

Valley switching is active in all operating modes.

To prevent high frequency operation at lower loads, the quasi-resonant operation switches

to discontinuous mode operation with valley skipping. When the frequency limit is

reached, the quasi-resonant operation changes to DCM with valley skipping. The

frequency limit reduces the MOSFET switch-on losses and conducted EMI.

At medium power levels, the controller enters Frequency Reduction (FR) mode. A Voltage

Controlled Oscillator (VCO) controls the frequency. The minimum frequency in this mode

is reduced to approximately 25 kHz. During frequency reduction mode, the primary peak

current is kept at an adjustable minimum level to maintain a high efficiency. Valley

switching is also active in this mode.

At very low power and standby levels, for which the switching frequency drops to below

25 kHz, the converter enters the burst mode. In burst mode, the switching frequency is

36.5 kHz. The primary peak current is fixed in burst mode.

In frequency reduction mode, the PFC controller switches off when the flyback switching

frequency has dropped to below 53 kHz and VPFCTIMER has reached 3 V. The flyback

maximum frequency changes linearly with the control VFBCTRL (see Figure 8). Hysteresis

is added to ensure a stable PFC switch-on and switch-off. In no-load operation, the

switching frequency is reduced to (almost) zero.

Fig 7.

Multimode operation flyback

SSL8516BT Datasheet(PDF) 13 Page - NXP Semiconductors