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TEA1751LT Datasheet(PDF) 10 Page - NXP Semiconductors |
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TEA1751LT Datasheet(HTML) 10 Page - NXP Semiconductors |
10 / 29 page 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 |
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