SR037SG Ver la hoja de datos (PDF) - Supertex Inc

Número de pieza

componentes Descripción

Fabricante

SR037SG

Inductorless, Dual Output Off-Line Regulators

Supertex Inc 

www.supertex.com

1235 Bordeaux Drive · Sunnyvale · CA · 94089 · Telephone (408) 744-0100 · Fax (408) 222-4895

Technical Bulletin: SR03x EMI Reduction

SR03-based power supplies may create conducted EMI into the AC power line that exceeds FCC and CISPR requirements.

This bulletin describes one technique to reduce EMI, allowing SR03-based supplies to comply with applicable requirements.

Conducted EMI is largely due to the short, high-current pulse imposed on the AC line when the pass MOSFET turns on.

Smoothing out this current pulse reduces the harmonic content of the current drawn from the AC line, thus reducing

conducted EMI. Placing a simple RC filter before the MOSFET gate smoothes out the pulse.

120/230VAC

50/60Hz

P6KE

400CA

EMI Suppressor Circuit

VN2460

EMI

Suppressor

CG

220pF

RG

180kΩ

VUNREG

CUNREG

220µF

VIN

GATE

SR03x SOURCE

VREG

GND

VREG

CREG

1µF

The values for RG and CG may need adjustment depending on the characteristics of the chosen MOSFET and the value of

CUNREG. (Higher values of CUNREG generally produce higher EMI as capacitor recharge times are shorter.) The idea is to

select values of R and C to soften the edges of the current pulse, as shown below. It may be tempting to forego C G, relying

instead on the MOSFETs’ input capacitance. However, high dV/dt when power is first applied may cause the MOSFET to turn

on due to CRSS, damaging the FET. CG protects against this possibility. Note that extending the turn-off time at the rising

edge of the rectified AC increases the voltage drop across the FET, decreasing efficiency somewhat.

AC Line Current – Turn-off Edge

Without EMI

Suppressor

With EMI

Suppressor

Share Link: