4116 Datasheet, PDF (5/12 Pages) Fairchild Semiconductor – A Fairchild Power Switch

APPLICATION NOTE
Figure of OCL Operation
300ns
Minimum Turn-on Time
1S
2R
Q` ³
Latch
1
+³
-²
OCL Level
Rsense
0
0
Figure 2-5. Over Current Latch (OCL)
3. Display Power Management
Signalling (DPMS) Design Method
With high interest in power management recently, much
effort has been concentrated in implementing the DPMS
AN4116
mode. The FS6S series uses burst mode for DPMS in order
to achieve cost effectiveness and minimize the power
consumption.
3.1 Burst Mode Operation
The FS6S-series has a particularly useful function for the
DPMS mode: burst mode operation. Normally, customers
use an auxiliary power system for DPMS in large monitors.
This method can lower power consumption but increases
costs. The FS6S-series can drop the output voltage with only
minimal external components by using burst mode.
This reduces power loss in DPMS mode.
In the DPMS mode, Vfb is pulled low by the external
micro-controller.
3.2 Implementation of the Burst Mode
The required circuit for implementing the burst mode is
shown in Figure 4-1. Q1, D1, Rx, R5 and R6 are added to the
secondary feedback network. During normal operation, Q1
is on, which isolates Rx from the feedback network.
Vo2 is sensed and the amplified error is transferred to the
primary side through the photo coupler. By turning off Q1,
Rx is connected to the feedback network.
The error amplifier increases the current through the photo
coupler, and thus Vfb of the FS6S-series drops to zero.
Therefore no additional opto coupler is required to switch
into burst mode. Rx can be calculated by the following
equation when KA431(LM431) is used as an error amp.
Rx < -^R-₂---⁷-_.-₅---^×-₍---_R-^R---₇-⁸----⁽_+---^V--_R--^o---₈-^l--₎--–--–--²--_R--^.-⁵--₈---–--_â‹---^VV-----^D_o---¹-₂---⁾
where Vo1 and Vo2 are the reduced voltages in burst mode.
Vo2
Vo1
R7
Ic
Ib
R1
Ia
R2
R3
Rx
R5
4
1
C1
3
2
R8
Micom signal
8
KA431
D1
Q1
R6
Figure 3-1. Rx Setting circuit for Burst mode operation
©2002 Fairchild Semiconductor Corporation
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