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DN91 डेटा पत्रक PDF( Datasheet डाउनलोड )


डेटा पत्रक - Synchronous rectification improves set top box power supply efficiency - Diodes

भाग संख्या DN91
समारोह Synchronous rectification improves set top box power supply efficiency
मैन्युफैक्चरर्स Diodes 
लोगो Diodes लोगो 
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DN91 pdf
DN91
main output channel is closed loop regulated through the optocoupler U2. LC post filters on each
output remove switching noise and minimize ripple level.
KBP 206 G
BR
NTC
10 Ω
R9
47 kΩ
C 15
33 μF
400 V
R11
47 Ω
C14
10 n F
1 kV
R 10
68 Ω
L3
2 × 5mH
D6
PR 1507 G
22 Ω
R 12
F1 X2-C
C 13 D 5
22 μF
R 13
L N 4. 7kΩ
U1
HV Vcc
D
GND FB
T1
P1 S 2
S1
S3
Aux
S4
S160
L5
D1
R2
47 Ω
C4
10 nF
D2
YG 811 R 04
L4
3 .3μ H
330 μ F
C2
L1
3. 3μ H
C5
1000 μ F
1000 μ F
C6
330 μ F
C3
+ 12 V
R tn
+ 5V
R tn
C 7 C8
D3
150 μ F
150 μ F
B1100
D4
YG811 R 04
R4
47 Ω
C Y1
2 .2nF
C1
10n F
200 Ω
R8
R3
L2
3. 3μ H
C 9 C 10
1000 μF 1000 μ F
C 11
R7
-20 V
+ 3. 3V
R5
20 kΩ
O pto
U2
10 kΩ
U3
Z T L431
0 .1 μF
R6
10 kΩ
Figure 2 - Typical set top box power supply
For set top box power supplies, it is common to stack secondary windings with the same polarity
and share a common source. This gives better voltage regulation between the outputs. In Figure
2, the winding for the 5V output will provide the return to ground whilst forming part of the
winding for the 12V output. This also helps to keep the total number of secondary winding turns
to a minimum. The wire size for the 5V winding needs to be chosen to accommodate its own
maximum load current plus the output current of the 12V output stacked on top of it.
The example set top box power supply was specified for a nominal input voltage of 230Vac and
load profile as shown in table 1.
Table 1 - Set top box power supply load profile
Nominal
voltage
5V
3.3V
12V
-20V
Power
Nominal load
current
2.5A
2A
500mA
60mA
26.3W
Maximum load
current
3.25A
2.5A
500mA
60mA
31.7W
Minimum load
current
1.25A
1A
125mA
20mA
11.05W
Function
Tuner/Demodulator
Audio & Video CODEC,
Video DAC, Memory, TVI
TDMS
Video and Audio Amp
Critically, much of the power supply heat generation and inefficiency is caused by Schottky
diodes, D2 and D4 on the 5V and 3.3V high current outputs. Replacing the diodes with more
efficient MOSFETs is recognized as a clear means of dramatically improving power supply
efficiency, thereby removing the need for bulky heat sinks and reducing the size and weight of the
www.zetex.com
www.diodes.com
2 Issue 1 - November 2008
© Diodes Incorporated 2008

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