EPR-18 Datasheet, PDF (8/28 Pages) Power Integrations, Inc. – Engineering Prototype Report for EP-18 10 W, Multiple Output, Isolated Power Supply with

10 W, Multiple Output, Isolated Power Supply
05-Dec-2002
disrupted for one second (LEDs blinked indicating the operation of the overvoltage
shutdown feature) when applying the 2 kV, 2 Ω differential pulse and the 4 kV, 2 Ω
differential pulses (L1/GND, L2/GND) and were unaffected during the 4 kV, 12 Ω
common-mode pulses (L1, L2/GND).
The switching frequency jitter of TOP243 (U1) allows the unit to meet worldwide
conducted EMI standards using a low cost, common-mode inductor (L1) in combination
with a small value capacitor (C15). Careful transformer construction and PCB layout
eliminate the need for a Y-rated capacitor between primary and secondary. Removal of
the Y cap is necessary in voice applications to eliminate line frequency audio hum
(“ground loops”). The common-mode inductance of L1 and the transformer construction
attenuate common-mode conducted emission currents caused by the switching
waveform on the DRAIN of U1, charging and discharging various stray capacitances.
The differential inductance of L1 together with C15 attenuate differential-mode emission
currents caused by the fundamental and harmonics of the primary current waveform.
The power supply passed the conducted EMI test (CISPR22B). The extended scan (to
100 MHz) was performed to detect high frequency peaks that could cause problems in
radiated emissions. A vertical and a horizontal bobbin transformer were both evaluated
for EMI. The vertical bobbin had slightly lower EMI and was selected for the final
prototype.
Power Integrations, Inc.
Tel: [phone] Fax: [phone]
www.powerint.com
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