TEA1751LT View Datasheet(PDF) - NXP Semiconductors.

Part Name

Description

Manufacturer

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

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

VFBCTRL

014aaa159

7.3.2 Valley switching (HV pin)

A new cycle starts when the external MOSFET is switched on. VFBSENSE and VFBCTRL

determine the on-time. The MOSFET is then switched off and the secondary stroke starts.

After the secondary stroke, the drain voltage shows an oscillation with a frequency of

approximately:

f = -------------------------1-------------------------

(3)

2    Lp  Cd

where Lp is the primary self-inductance of the flyback transformer and Cd is the

capacitance on the drain node.

When the internal oscillator voltage is high and the secondary stroke 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 4. High frequency operation makes small and cost-effective

magnetic components possible.

P

=

1--

2



Cd



V2



f

(4)

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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