TEA1751T_LT_2

© NXP B.V. 2009. All rights reserved.

Product data sheet

Rev. 02 — 23 December 2009

10 of 29

NXP Semiconductors

TEA1751T; TEA1751LT

GreenChip III SMPS control IC

7.2.6 Low power mode

When the output power of the flyback converter (see Section 7.3) is low, the flyback

converter switches over to frequency reduction mode. When frequency reduction mode is

entered by the flyback controller, the power factor correction circuit is switched off to

maintain high efficiency.

During low power mode operation the PFCCOMP pin is clamped to a minimal voltage of

2.7 V (typical) and a maximum voltage of 3.9 V (typical). The lower clamp voltage limits

the maximum power that is delivered when the PFC is switched on again. The upper

clamp voltage ensures that the PFC can return to its normal regulation point in a limited

amount of time when returning from low power mode.

As soon as the flyback converter leaves the frequency reduction mode, the power factor

correction circuit restores normal operation. To prevent continuous switching on and off of

the PFC circuit, a small hysteresis is build in, (60 mV (typical) on the FBCTRL pin).

7.2.7 Dual boost PFC

The PFC output voltage is modulated by the mains input voltage. The mains input voltage

is measured via the VINSENSE pin. The current is sourced from the VOSENSE pin if the

voltage on the VINSENSE pin drops below 2.2 V (typical). To ensure the stability of the

switch-over 200 mV is inserted around the 2.2 V, see Figure 6.

For low VINSENSE input voltages, the output current is 15

μA (typical). This output

current, in combination with the resistors on the VOSENSE pin, sets the lower PFC output

voltage level at low mains voltages. At high mains input voltages the current is switched to

zero. The PFC output voltage will then be at its maximum. As this current is zero in this

situation, it does not effect the accuracy of the PFC output voltage.

For proper switch-off behavior, the VOSENSE current is switched to its maximum value,

(15

μA (typical)), as soon as the voltage on pin VOSENSE drops below 2.1 V (typical).

Fig 5.

Soft start-up of PFC

SOFT START

CONTROL

OCP

11

PFCSENSE

0.5 V

Istartup(soft)PFC ≤ 60 μA

S1

RSS1

CSS1

RSENSE1

014aaa157