tea1553t NXP Semiconductors, tea1553t Datasheet - Page 11

• Manufacturer Part Number: tea1553t
• Description: Tea1553t Greenchip Ii Smps Control Ic
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1553T_1
Product data sheet
7.10 Valley switching
V
Where N
the transformer.
Current I
The value of the demagnetization resistor, R
transformer, thus making an accurate OVP possible.
(See
‘on-time’ (which is determined by the ‘sense’ voltage and the internal control voltage), the
switch is opened and the secondary stroke starts. After the secondary stroke, the drain
voltage shows an oscillation with a frequency of approximately
where L
the drain node.
As soon as the 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. This method
is called valley detection.
the signal indicating the secondary stroke and the oscillator signal.
In an optimum design, the reflected secondary voltage on the primary side will force the
drain voltage to zero. Thus, zero voltage switching is possible, preventing large capacitive
losses
and cost effective inductors.
trip OVPFCAP
Figure
P
p
ovp
s
is the primary self inductance of the transformer and C
=
is the number of secondary turns and N
1
-- -
2
is internally trimmed.
9.) A new cycle starts when the power switch is switched on. After the
=
C
-----------
N
N
aux
V
S
2
Rev. 01 — 3 July 2007
f
I
Figure 9
ovp
, and allowing high frequency operation, which results in small
R
DEM
shows the drain voltage together with the valley signal,
+
V
CL pos
DEM
, can be adjusted to the turns ratio of the
aux
is the number of auxiliary turns of
GreenChip II SMPS control IC
---------------------------------------------------- -
2
d
is the capacitance on
TEA1553T
© NXP B.V. 2007. All rights reserved.
1
L
p
C
d
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