TEA1751(L)T View Datasheet(PDF) - NXP Semiconductors.

Part Name

Description

Manufacturer

TEA1751(L)T

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

NXP Semiconductors. 

NXP Semiconductors

TEA1751T; TEA1751LT

GreenChip III SMPS control IC

fsw(fb)max

switching frequency

PFC off

frequency

reduction

PFC on

discontinuous

with valley

switching

quasi resonant

1.5 V

Fig 8. Frequency control of flyback part

VFBCTRL

014aaa159

7.3.2 Valley switching (HV pin)

Refer to Figure 9. A new cycle starts when the external MOSFET is activated. After the

on-time (determined by the FBSENSE voltage and the FBCTRL voltage), the MOSFET is

switched off and the secondary stroke starts. After the secondary stroke, the drain voltage

shows an oscillation with a frequency of approximately -------------------------1-------------------------- where Lp is

(2 × π × (Lp × Cd))

the primary self-inductance of the flyback transformer and Cd is the capacitance on the

drain node.

As soon as the internal oscillator voltage is high again and the secondary stroke has

ended, the circuit waits for the lowest drain voltage before starting a new primary stroke.

Figure 9 shows the drain voltage, valley signal, secondary stroke signal and the internal

oscillator signal.

Valley switching allows high frequency operation as capacitive switching losses are

reduced, see Equation 1. High frequency operation makes small and cost-effective

magnetics possible.

⎛

⎝

P

=

1--

2

×

Cd

×

V2

×

f⎠⎞

(1)

TEA1751T_LT_2

Product data sheet

Rev. 02 — 23 December 2009

© NXP B.V. 2009. All rights reserved.

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