tea1781 NXP Semiconductors, tea1781 Datasheet - Page 13

• Manufacturer Part Number: tea1781
• Description: Greenchip Pc Secondary Control Ics
• Manufacturer: NXP Semiconductors

NXP Semiconductors
TEA1781_82_1
Preliminary data sheet
7.8 Output voltage regulation
The output voltage is regulated to the required voltage level via a current mode control
loop.
When the secondary side transformer voltage is negative, switch SB is turned off to avoid
negative currents, see
and the output current in the secondary coil has dropped below a certain value, switch SB
is turned on again. This value is proportional to the difference between the output voltage
and the reference voltage, increased with a ramp voltage. This type of regulation is called
current mode control. A ramp voltage is required to stabilize the control loop for duty
cycles smaller than 0.5 and is called slope compensation.
The output current is measured using the output inductor series resistance. When the
parallel RC network is
voltage across the inductors resistance. L and R
resistance value of the output inductor.
Fig 11. Output voltage regulation
V
(1) WND_SEC_x: The “x” stands for either 1 or 2
(2) GSB_x, DF_x, FSB_x, GSF_x, CS_x:
(3) VOUT_x: The “x” stands for either 3V3, 5V, 12V1 or 12V2.
WND_SEC_x
Control
Q R
SR
ResetSB
The “x” for these pins and symbols stands for either 3V3, 5V or 12V
S
Drive
SB
I-control
Rev. 01 — 13 February 2009
VDD
SF
Figure
R C
I
=
11. Once the secondary side transformer voltage is positive
----- -
R
L
L
I
the voltage across the parallel capacitor equals the
V/I
R
L
V
ref
C
V
WND_SEC_x
ResetSB
TEA1781T; TEA1782T
V
VOUT_x
SB
SF
L
GreenChip PC secondary control ICs
represent the inductance and the
© NXP B.V. 2009. All rights reserved.
V
0
V
"1"
"0"
closed
open
closed
open
014aaa191
rst
INDC / N
13 of 32
N