tea1752t NXP Semiconductors, tea1752t Datasheet - Page 15

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

NXP Semiconductors
TEA1752T_LT
Product data sheet
7.3.2 Valley switching (HV pin)
Figure 10
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
the primary self-inductance of the flyback transformer and C
drain node.
When 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.
shows the drain voltage, valley signal, secondary stroke signal and the internal oscillator
signal.
Valley switching allows high frequency operation as capacitive switching losses are
reduced (see
magnetics possible.
⎛
⎝
P
Fig 9.
=
1
-- -
2
×
C
Frequency control of flyback part
shows that a new cycle starts when the external MOSFET is activated. After the
d
switching
frequency
f
sw(fb)max
×
flyback
Equation
V
2
All information provided in this document is subject to legal disclaimers.
×
f
⎞
⎠
Rev. 02 — 24 June 2010
1). High frequency operation makes small and cost-effective
frequency
reduction
PFC off
1.5 V
PFC on
TEA1752T; TEA1752LT
discontinuous
with valley
switching
V
FBCTRL
-------------------------------------------------- -
(
2
GreenChip III SMPS control IC
×
π
d
quasi-resonant
is the capacitance on the
×
1
(
L
p
×
C
© NXP B.V. 2010. All rights reserved.
014aaa746
d
)
)
where L
Figure 10
15 of 34
p
is
(1)