TEA1750 NXP Semiconductors, TEA1750 Datasheet - Page 13

• Manufacturer Part Number: TEA1750
• Description: GreenChip III SMPS control IC
• Manufacturer: NXP Semiconductors

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NXP Semiconductors
TEA1750_2
Product data sheet
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7.3.2 Valley switching (HV pin)
a
s
h
In frequency reduction mode the PFC controller is switched to burst mode operation and
the flyback maximum frequency changes linearly with the control voltage on the FBCTRL
pin (see
has a 50 mV (typ) hysteresis. At no load operation the switching frequency of the flyback
can be reduced to (almost) zero.
Refer to
on-time (determined by the FBSENSE voltage and the FBCTRL voltage), the MOSFET is
switched off and the secondary stroke starts. After the secondary stroke, the drain voltage
shows an oscillation with a frequency of approximately
where L
capacitance on the drain node.
As soon as the internal oscillator voltage is high again and the secondary stroke has
ended, the circuit waits for the lowest drain voltage before starting a new primary stroke.
Figure 9
oscillator signal.
Valley switching allows high frequency operation as capacitive switching losses are
reduced, see
magnetics possible.
Fig 8.
P
e
switching frequency
=
e
1
-- -
2
t
p
Figure
Figure 8
shows the drain voltage, valley signal, secondary stroke signal and the internal
C
Frequency control of flyback part
is the primary self inductance of the flyback transformer and C
4
d
f
sw(fb)max
u
Equation
V
9. A new cycle starts when the external MOSFET is activated. After the
2
.
). For stable on-off switching of the PFC burst mode, the FBCTRL pin
c
f
PFC burst mode
Rev. 02 — 15 December 2008
o
frequency
reduction
1. High frequency operation makes small and cost-effective
m
1.5 V
PFC on
discontinuous
with valley
switching
V
FBCTRL
--------------------------------------------------- -
2
GreenChip III SMPS control IC
quasi resonant
1
L
p
014aaa026
TEA1750
C
© NXP B.V. 2008. All rights reserved.
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