TEA1750T/N1,518【PDF 12/29 页】IC PFC CONTROLLER DCM16SOIC

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Sheet目录46

8页 9页 10页 11页 [12页]13页 14页 15页 16页

TEA1750_2

Product data sheet

Rev. 02 15 December 2008

12 of 29

NXP Semiconductors

TEA1750

GreenChip III SMPS control IC

7.2.11 Driver (pin PFCDRIVER)

The driver circuit to the gate of the power MOSFET has a current sourcing capability of

typically 500 mA and a current sink capability of typically 1.2 A. This permits fast turn-on

and turn-off of the power MOSFET for efcient operation.

7.3 Flyback controller

The TEA1750 includes a controller for a yback converter. The yback converter operates

in quasi-resonant or discontinuous conduction mode with valley switching. The auxiliary

winding of the yback transformer provides demagnetization detection and powers the IC

after start-up.

7.3.1 Multi mode operation

The TEA1750 yback controller can operate in multi modes; see

Figure

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

stroke is started after demagnetization of the transformer current. In quasi-resonant mode

switching losses are minimized as the converter only switches on when the voltage across

the external MOSFET is at its minimum (valley switching, see also

Section

7.3.2).

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

to discontinuous mode operation with valley skipping in which the switching frequency is

limited for EMI to f

sw(fb)(max)

(125 kHz typ). Again, the external MOSFET is only switched

on when the voltage across the MOSFET is at its minimum.

At very low power and standby levels the frequency is controlled down by a voltage

controlled oscillator (VCO). The minimum frequency can be reduced to zero. During

frequency reduction mode, the primary peak current is kept at a minimal level of Ipkmax/4

to maintain a high efciency. (Ipkmax is the maximum primary peak current set by the

sense resistor and the maximum sense voltage.) As the primary peak current is low in

frequency reduction mode operation (Ipk = Ipkmax/4), no audible noise is noticeable at

switching frequencies in the audible range. Valley switching is also active in this mode.

Fig 7. Multi mode operation yback

discontinuous

with valley

switching

quasi resonant

PFC burst mode

frequency

reduction

sw(fb)max

output power

switching frequency

014aaa025

PFC on

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