DI-89
DI-116
•
•
Select the value of VR1 and VR2 to limit the maximum
voltageduringanopenloopfault. ResistorR13provides
a bias current so that the Zeners are operated closer to
their test current. This bias current also acts as a pre-
load.
For improved cross-regulation, feedback for the power
supply is provided from both the 5 V and 12 V output
into the voltage reference U4 via R14 and R15.
Key Design Points
•
The primary clamp of D5, R1, VR3, R2 and C3 is an
optimized RCD clamp. During full load, VR3 limits the
maximum voltage across C3. At light-load or no-load, as
the effective switching frequency is reduced, VR3 prevents
C3 from discharging completely. This prevents the clamp
network from appearing as a significant load. The use of
a fast vs. ultra-fast diode for D5 improves efficiency by
recycling some of the leakage energy to the output.
TRANSFORMER PARAMETERS
EE25, N67 or equivalent, gap
Core Material
80
for ALG of 105 nH/T2
EN55022B Limits
70
5+5 pin vertical (Yih-Hwa YW-
360-02B)
QP
AV
60
50
Bobbin
Bias: 27T, 29 AWG
40
30
20
10
0
Primary: 105T, 32 AWG
Shield: 2T, 100 mm × 9 mm ×
1 mil Cu foil
+5 V: 5T, 2 × 24 AWG T.I.W.
+12 V: 6T, 25 AWG T.I.W.
-12 V: 11T, 32 AWG T.I.W.
-24 V: 11 T, 32 AWG T.I.W.
Winding Details
-10
Winding Order
(pin numbers)
1 mm tape margin, bias (4-
5), tape, primary (3-2), shield
(2-NC), tape, +5 V (6-7), +12 V
(8-6), tape, -12 V (7-10), -24 V
(10-9), tape
-20
0.15
1.0
10.0
100.0
MHz
Figure 2. Worst-Case Conducted EMI Results
(Output Connected to Safety Earth ground).
Inductance
Primary: 1.15 mH - 0/+10%
Leakage: 70 µH (max)
Table 1. Transformer Design Parameters.
For the latest updates, visit www.powerint.com
Power Integrations reserves the right to make changes to its products at any time to improve reliability or
manufacturability. Power Integrations does not assume any liability arising from the use of any device or circuit
described herein. POWER INTEGRATIONS MAKES NO WARRANTY HEREIN AND SPECIFICALLY DISCLAIMS ALL
WARRANTIES INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF MERCHANTABILITY, FITNESS
FOR A PARTICULAR PURPOSE, AND NON-INFRINGEMENT OF THIRD PARTY RIGHTS. The products and applications
illustrated herein (transformer construction and circuits external to the products) may be covered by one or more U.S.
and foreign patents or potentially by pending U.S. and foreign patent applications assigned to Power Integrations. A
complete list of Power Integrations' patents may be found at www.powerint.com. Power Integrations grants its
customers a license under certain patent rights as set forth at http://www.powerint.com/ip.htm.
Power Integrations
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San Jose, CA 95138
Phone: 1-408-414-9200
Apps: 1-408-414-9660
Apps Fax: 1-408-414-9760
The PI logo, TOPSwitch, TinySwitch, LinkSwitch, DPA-Switch, PeakSwitch, EcoSmart,
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Other trademarks are property of their respective companies. ©Copyright 2006, Power Integrations, Inc.
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