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© 2019 ROHM Co., Ltd.
No. 61UG024E Rev.002
Jul. 2021
User’s Guide
BM2P141X-EVK-001
4.3 Output Capacitor C7, C8
– Continued
Select a rated current of 0.59 A or more.
The output capacitor C7 used a rated ripple current of 1.24 A at 680 μF / 25 V.
C8 has added a 0.1 μF ceramic capacitor to reduce switching noise.
5 Resistor Selection
5.1 Discharge Resistor : R1,R2,R3
The resistor is for discharging X - Capacitor (C1). Considering withstand voltage, 3 pcs of chip resistance of ROHM
product MCR18 (200 V withstand voltage) are connected in series. 220 kΩ is used in 3 pcs in series so that it becomes 45
V or less after 1 second after turning off the power supply.
5.2 Bleeder Resister : R4
Because it is indirectly fed back to the output voltage, the output voltage increases at light load. This board uses bleeder
resistance for its improvement. Reducing the resistance value improves the rise in the output voltage of the light load, but
increases the power loss. 10 kΩ / 0.25 W is used.
6 EMI Filter Selection
As a measure against "Conducted Emission", Input filter is composed of X-Capacitor: C1 and common mode filter LF1.
X-Capacit
or uses 0.22 μF / X 2. The common mode filter uses 13 mH (Min) / 1 A.
As a measure against "Radiated Emission", Input filter is composed of Y-Capacitor: C2, C3 and a common mode filter LF2.
Y - Capacitor uses 2200 pF / Y1 and connects the midpoint to the output capacitor so that high frequency noise is not
propagated from the input. Moreover, the common mode filter uses 60 μH (Min) / 1 A with good characteristics of the 100
MHz band. If "Radiated Emission" does not have a problem in the state that it is loaded in the set, C2, C3, LF2 are
unnecessary.
