DI-29
Key Design Points
Transformer Parameters
• For nominal under-voltage set point VUV:
R1 = (VUV-2.35 V)/50µA. VOV = (R1×135 µA)+2.5 V.
• Zener VR1 voltage is 130 V to safely limit the DRAIN
voltage below VDSS of 200 V.
PR1408
Core Material
Bobbin
Siemens N87
Gap for 340 nH/T2
P1408 8 pin (B&B B-096 or equivalent)
• Opto U2 should have a CTR of between 100% and 200%
for optimum loop stability.
• Set resonance of L2 and C13 + C14 to beyond loop
crossover frequency (typically 5% to 10% of switching
frequency).
• Good layout practices should be followed:
- Locate C5, C6 and R4 close to U1, with grounds
returned to the SOURCE pin.
Primary: 6T + 6T, 2 x 27 AWG
Secondary: 3T, 4 x 25 AWG
Bias: 6T, 32 AWG
Winding Details
Primary (4-FL), tape, Bias (2-3), tape,
Secondary (5,6-7,8), tape,
Primary (FL-1), tape
Winding Order
(pin numbers)
Primary: 49 µH ±10%, Leakage: 1 µH (max)
Inductance
Primary Resonant
Frequency
3.8 MHz (minimum)
- Primary return should be connected to the DPA-Switch
tab, not the SOURCE pin.
- Minimize the primary and secondary loop areas to
reduce parasitic leakage inductance.
Table 1. Transformer Construction Information.
100
80
60
40
20
36 VDC
48 VDC
60 VDC
72 VDC
0
0
5
10
Output Current (W)
Figure 2. Efficiency vs. Output Power.
15
20
25
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Power Integrations does not assume any liability arising from the use of any device or circuit described herein, nor does it convey any
license under its patent rights or the rights of others. The products and applications illustrated herein (including circuits external to the
products and transformer construction) 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.
The PI Logo, TOPSwitch, TinySwitch, LinkSwitch and EcoSmart are registered trademarks of Power Integrations, Inc.
PI Expert is a trademark of Power Integrations Inc. ©Copyright 2002, Power Integrations, Inc.
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