tea1752t NXP Semiconductors, tea1752t Datasheet - Page 14

• Manufacturer Part Number: tea1752t
• Description: Greenchip Iii Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1752T_LT
Product data sheet
At high output power the converter switches to quasi-resonant mode. The next converter
stroke is started after demagnetization of the transformer current. In quasi-resonant mode
switching losses are minimized as the converter only switches on when the voltage across
the external MOSFET is at its minimum (valley switching, see
To prevent high frequency operation at lower loads, the quasi-resonant operation changes
to discontinuous mode operation with valley skipping, in which the EMI switching
frequency is limited to f
switched on when the voltage across the MOSFET is at its minimum.
At very low power and standby levels the frequency is reduced by a Voltage Controlled
Oscillator (VCO). The minimum frequency can be reduced to zero. During frequency
reduction mode the primary peak current is kept constant at a minimum adjustable level to
control the PFC on-power and off-power levels. I
generally be greater than I
primary peak current is low in frequency reduction operation, no audible noise is
noticeable at switching frequencies in the audible range. Valley switching is also active in
this mode.
In frequency reduction mode the PFC controller is switched off and the flyback maximum
frequency changes linearly with the control voltage on the FBCTRL pin (see
For stable on and off switching of the PFC, hysteresis has been added. At no load
operation the switching frequency can be reduced to (almost) zero.
Fig 8.
Multimode operation flyback
frequency
switching
flyback
125 kHz
86 kHz
48 kHz
All information provided in this document is subject to legal disclaimers.
I
adjust
sw(fb)max
pmin
Rev. 02 — 24 June 2010
pmax
frequency
reduction
PFC off
/ 4, so a high efficiency at low loads is guaranteed. As the
(125 kHz typical). Again, the external MOSFET is only
TEA1752T; TEA1752LT
PFC on
pmin
discontinuous
with valley
switching
in frequency reduction mode will
GreenChip III SMPS control IC
output power
Section
quasi-resonant
014aaa745
7.3.2).
© NXP B.V. 2010. All rights reserved.
Figure 9
14 of 34
).