TEA1751T_LT_2
?NXP B.V. 2009. All rights reserved.
Product data sheet
Rev. 02  23 December 2009 
9 of 29
NXP Semiconductors
TEA1751T; TEA1751LT
GreenChip III SMPS control IC
7.2.3   Frequency limitation
To optimize the transformer and minimize switching losses, the switching frequency is 
limited to f
sw(PFC)max
. If the frequency for quasi-resonant operation is above the f
sw(PFC)max
 
limit, the system switches over to discontinuous conduction mode. Also here, the PFC 
MOSFET is only switched on at a minimum voltage across the switch (valley switching).
7.2.4   Mains voltage compensation (VINSENSE pin)
The mathematical equation for the transfer function of a power factor corrector contains 
the square of the mains input voltage. In a typical application this results in a low 
bandwidth for low mains input voltages, while at high mains input voltages the Mains 
Harmonic Reduction (MHR) requirements may be hard to meet.
To compensate for the mains input voltage influence, the TEA1751(L)T contains a 
correction circuit. Via the VINSENSE pin the average input voltage is measured and the 
information is fed to an internal compensation circuit. With this compensation it is possible 
to keep the regulation loop bandwidth constant over the full mains input range, yielding a 
fast transient response on load steps, while still complying with class-D MHR 
requirements.
In a typical application, the bandwidth of the regulation loop is set by a resistor and two 
capacitors on the PFCCOMP pin.
7.2.5   Soft start-up (pin PFCSENSE)
To prevent audible transformer noise at start-up or during hiccup, the transformer peak 
current, I
DM
, is increased slowly by the soft start function. This can be achieved by 
inserting R
SS1
 and C
SS1
 between pin PFCSENSE and current sense resistor R
SENSE1
. 
An internal current source charges the capacitor to V
PFCSENSE
= I
start(soft)PFC
?R
SS1
. The 
voltage is limited to V
start(soft)PFC
.
The start level and the time constant of the increasing primary current level can be 
adjusted externally by changing the values of R
SS1
 and C
SS1
.
The charging current I
start(soft)PFC
 flows as long as the voltage on pin PFCSENSE is 
below 0.5 V (typ). If the voltage on pin PFCSENSE exceeds 0.5 V, the soft start current 
source starts limiting current I
start(soft)PFC
. As soon as the PFC starts switching, the 
I
start(soft)PFC
 current source is switched off; see Figure 5
.
?SPAN class="pst TEA1751T-N1-518_2409373_9">softstart    3   R
SS1
C
SS1
    
    
| 相關代理商/技術參數 | 參數描述 | 
| TEA1752LT | 制造商:PHILIPS 制造商全稱:NXP Semiconductors 功能描述:GreenChip III SMPS control IC | 
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