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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patent applications assigned to Power Integrations. A complete list of Power Integrations’ patents may be found at www.powerint.com.
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PI Expert is a trademark of Power Integrations Inc. ©Copyright 2002, Power Integrations, Inc.
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