TEA1751T/N1,518【PDF 8/29 页】IC CTRLR GREENCHIP SMPS 16-SOIC

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Sheet目录46

4页 5页 6页 7页 [8页]9页 10页 11页 12页

TEA1751T_LT_2

Product data sheet

Rev. 02 23 December 2009

8 of 29

NXP Semiconductors

TEA1751T; TEA1751LT

GreenChip III SMPS control IC

7.1.4 Fast latch reset

In a typical application the mains can be interrupted briefly to reset the latched protection.

The PFC bus capacitor, C

bus

, does not have to discharge for this latched protection to

reset.

Typically the PFC bus capacitor, C

bus

, has to discharge for the V

to drop to this reset

level. When the latched protection is set, the clamping circuit of the VINSENSE circuit is

disabled. (see also Section 7.2.9

) As soon as the VINSENSE voltage drops below

750 mV (typical) and after that is raised to 870 mV (typical), the latched protection is reset.

The latched protection is also reset by removing both the voltage on pin V

and on

pin HV.

7.1.5 Overtemperature protection

An accurate internal temperature protection is provided in the circuit. When the junction

temperature exceeds the thermal shutdown temperature, the IC stops switching. As long

as OTP is active, the capacitor C

VCC

is not recharged from the HV mains. The OTP circuit

is supplied from the HV pin if the V

supply voltage is not sufficient.

OTP is a latched protection. It can be reset by removing both the voltage on pin V

and

on pin HV or by the fast latch reset function. (See Section 7.1.4

)

7.2 Power factor correction circuit

The power factor correction circuit operates in quasi-resonant or discontinuous

conduction mode with valley switching. The next primary stroke is only started when the

previous secondary stroke has ended and the voltage across the PFC MOSFET has

reached a minimum value. The voltage on the PFCAUX pin is used to detect transformer

demagnetization and the minimum voltage across the external PFC MOSFET switch.

7.2.1 t

control

The power factor correction circuit is operated in t

control. The resulting mains harmonic

reduction of a typical application is well within the class-D requirements.

7.2.2 Valley switching and demagnetization (PFCAUX pin)

The PFC MOSFET is switched on after the transformer is demagnetized. Internal circuitry

connected to the PFCAUX pin detects the end of the secondary stroke. It also detects the

voltage across the PFC MOSFET. The next stroke is started when the voltage across the

PFC MOSFET is at its minimum in order to reduce switching losses and ElectroMagnetic

Interference (EMI) (valley switching).

If no demagnetization signal is detected on the PFCAUX pin, the controller generates a

zero current signal (ZCS), 50 約 (typical) after the last PFCGATE signal.

If no valley signal is detected on the PFCAUX pin, the controller generates a valley signal

4 約 (typical) after demagnetization was detected.

To protect the internal circuitry during lightning events, for example, it is advisable to add a

5 k?series resistor to this pin. To prevent incorrect switching due to external disturbance,

the resistor should be placed close to the IC on the printed-circuit board.

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