tea1781 NXP Semiconductors, tea1781 Datasheet - Page 15

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

NXP Semiconductors
TEA1781_82_1
Preliminary data sheet
Table 4.
In Standby mode, a higher I
system. In Normal mode, the systems duty cycle/frequency is defined by the primary
controller being related to the inverse of the input voltage. The OPTO control block
diagram is given in
At system start-up, the secondary controllers are supplied via a rectified secondary
winding voltage. Therefore the secondary controllers are started up after the primary side
has started up.
As the voltage at the OPTO pin is zero when the secondary controllers are not yet
supplied, the primary side starts up at the minimum duty cycle/frequency. Once the
secondary side has started, it increases the operating duty cycle/frequency of the system
depending on the standby load and mode of operation.
When the system is in Normal mode, switch S3 is closed and the opto coupler current is
increased to I
primary controller TEA1771T and is related to the inverse of the input voltage.
When the secondary protection mode fails, switch S4 is closed and a maximum current
flows through the opto coupler. This high current triggers the primary controller into
Protection mode, switching off the primary main switch. A safe restart of the system will
follow. This implies that the system will start up again after all the supply voltages, primary
and secondary, are below their UVLO levels resulting in a total reset of the system.
In Standby mode, the system minimizes the duty cycle of the primary control switch to
reduce the magnetic losses in the transformer to a minimum. As the primary duty cycle
has to be at least equal to the secondary duty cycle, the system will equalize both duty
cycles in Standby mode. This is regulated in the opto control block.
Mode of operation
Standby mode
Normal mode
System restart
Fig 13. TEA1782T OPTO control diagram
OPTO control modes
OPTO
(Normal mode). In this mode, the primary duty cycle is defined by the
Figure
DOWN
Rev. 01 — 13 February 2009
OPTO control
UP
13.
OPTO
current implies a higher duty cycle / frequency of the
S1
S2
TEA1781T; TEA1782T
Normal mode
S3
I
0 mA to
OPTO
3.5 mA
30 mA
PVCC
GreenChip PC secondary control ICs
V/I
off
I
014aaa193
S4
3.5 mA
OPTO
© NXP B.V. 2009. All rights reserved.
15 of 32