TEA1751LT Просмотр технического описания (PDF) - NXP Semiconductors.

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TEA1751LT

HV start-up DCM/QR flyback controller with integrated DCM/QR PFC controller

NXP Semiconductors. 

NXP Semiconductors

TEA1751LT

HV start-up flyback controller with integrated PFC controller

7.2.3 Frequency limitation

To optimize the transformer and minimize switching losses, the switching frequency is

limited to fsw(PFC)max. If the frequency for quasi-resonant operation is above the fsw(PFC)max

limit, the system switches over to DCM. The PFC MOSFET is only switched on at a

minimum voltage across the switch (valley switching).

7.2.4 Mains voltage compensation (VINSENSE pin)

The equation for the transfer function of a power factor corrector contains the square of

the mains input voltage. In a typical application, this results in a low bandwidth for low

mains input voltages and a high bandwidth for high mains input voltages.

To compensate for the mains input voltage influence, the TEA1751LT contains a

correction circuit. The average input voltage is measured using the VINSENSE pin and

the information is fed to an internal compensation circuit. Using this compensation, it is

possible to keep the regulation loop bandwidth constant over the mains input range. This

feature yields a fast transient response on load steps, while still complying with class-D

MHR requirements.

In a typical application, a resistor and two capacitors connected to the PFCCOMP pin set

the bandwidth of the regulation loop.

7.2.5 Soft-start-up (pin PFCSENSE)

To prevent audible transformer noise at start-up or during hiccup, the soft-start function

slowly increases the transformer peak current. This increase is achieved by inserting RSS1

and CSS1 between the PFCSENSE pin and the current sense resistor RSENSE1.

An internal current source charges the capacitor to:

VPFCSENSE = IstartsoftPFC  RSS1

(1)

The voltage is limited to Vstart(soft)PFC.

The start level and the time constant of the increasing primary current level are adjusted

externally by changing the values of RSS1 and CSS1.

soft–start = 3  RSS1  CSS1

(2)

The charging current Istart(soft)PFC flows as long as VPFCSENSE is below 0.5 V. If VPFCSENSE

exceeds 0.5 V, the soft-start current source starts limiting current Istart(soft)PFC. When the

PFC starts switching, the Istart(soft)PFC current source is switched off; see Figure 5.

TEA1751LT

Product data sheet

All information provided in this document is subject to legal disclaimers.

Rev. 3. — 9 January 2013

© NXP B.V. 2013. All rights reserved.

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