tea1553t NXP Semiconductors, tea1553t Datasheet - Page 12

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

NXP Semiconductors
TEA1553T_1
Product data sheet
7.11 Overcurrent protection
7.12 Overpower protection
I
The cycle-by-cycle peak drain current limit circuit uses the external source resistor to
measure the current accurately. This allows optimum size of the transformer core to be
determined (cost issue). The circuit is activated after the leading edge blanking time, t
The OCP protection circuit limits the ‘sense’ voltage to an internal level.
During the primary stroke, the rectified mains input voltage is measured by sensing the
current drawn from pin DEM. This current is dependent on the mains voltage, according to
the following formula:
Where:
The current information is used to adjust the peak drain current, which is measured via pin
ISENSE. The internal compensation is such that a maximum output power can be
achieved that is almost mains independent.
DEM
Fig 9. Signals for valley switching
(1) Start of new cycle at lowest drain voltage.
(2) Start of new cycle in a classical PWM system at high drain voltage.
------------- -
R
V
N
DEM
aux
=
-----------
N
secondary
N
oscillator
aux
N
-------------------------- -
p
stroke
valley
R
drain
DEM
V
mains
Rev. 01 — 3 July 2007
primary
stroke
secondary
stroke
secondary
ringing
GreenChip II SMPS control IC
(2)
TEA1553T
014aaa027
© NXP B.V. 2007. All rights reserved.
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