DI-89
DI-117
The built-in frequency jitter and E-ShieldTM techniques allow
simple EMI filtering to comply with EN55022B. Resistor R2
and C4 form an RC snubber to reduce high-frequency EMI.
Key Design Points
•
•
•
Verify maximum drain voltage is <650 V at high line,
maximum overload. Adjust values of R5, R6 and C5
accordingly. However, avoid making the clamp too
dissipative (low value of R5 and R6, and high value of
C5) as this will increase no-load consumption.
To prevent an increase in no-load consumption or false
OVP triggering, VR3 should be selected to conduct
only when the output voltage is outside the normal
regulationrange.ResistorR4preventsexcessivecurrent
from flowing into the BP/M pin.
Outputovervoltageprotection(OVP)isprovidedontheprimary
sidebysensingthevoltageoftheauxiliarytransformerwinding.
Shouldthemainfeedbackloopopen duetofailureofU2,thenU1
willlatchoffoncethecurrentintotheBP/Mpin(viaVR3)exceeds
6.5 mA. Diode D6 and capacitor C7 rectify and smooth the
output of the auxiliary winding. The value of VR3 is selected
to trigger the OVP latch when the main output, and hence the
auxiliaryoutputvoltage,risesabovethenormalregulationrange.
Once triggered, cycling the AC power resets the OVP latch.
Fast recovery glass-passivated diodes were selected for
D1 and D3 to reduce low frequency conducted EMI.
Fast diodes such as FR107 are also suitable.
To reduce no-load input power and thus increase light load
efficiency, resistor R3 feeds the supply current for U1 from the
auxiliary winding on the transformer.
TRANSFORMER PARAMETERS
EF20, N67 or equivalent, gap
Core Material
35
30
25
20
for ALG of 203 nH/T2
Bobbin
5+5 pin horizontal
Shield: 24T, 28 AWG
Primary: 62T, 31 AWG
Bias: 5T, 4 × 28 AWG
12 V: 7T, 23 AWG T.I.W.
Winding Details
15
10
5
3 mm tape margin, shield
(1-NC), tape, primary (3-1),
tape, bias (5-4), tape, 12 V
(10-9), tape
Winding Order
(Pin Numbers)
0
Primary: 790 µH ±7%
Leakage: 30 µH (max)
Inductance
-5
Primary Resonant
Frequency
50
100
0
650 kHz (min)
Time (ms)
Figure 2. Worst-Case Open Loop Output Overvoltage
(85 VAC, Full Load).
Table 1. Transformer Design Parameters.
T.I.W.: Triple Insulated Wire, NC: No Connection
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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Rev. A 09/06
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