EVHF900-P-00A –OFF LINE, SWITCHING REGULATOR
EVHF900-P-00A Rev. 1.1 www.MonolithicPower.com 7
4/11/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2017 MPS. All Rights Reserved.
CIRCUIT DESCRIPTION
The EVHF900-P-00A is configured for 5W triple
outputs in power meter application. The 8V
output rail can power the LCD for MCU power
supply. The demo board is proper for three
phase input power system.
FR1 is used to protect for the component failure
or some excessive short events, also it can
restrain the inrush current.
The CX1, CX2 and LX1 compose the EMI filter to
guarantee the conducted EMI meet the EN55022
criteria. CX1 is in series with CX2 for 420VAC
input. R3, R8 and R11 are used to discharge the
energy stored in CX1 and CX2 in 1 second for
safety requirement.
D3, D4, D7 and D8 compose the input stage to
commute the AC voltage to DC voltage.
The C6 and C8 are used for energy storage
reducing line noise and protecting against line
surge. R2, R6, R10 R12 and R20 are for
balancing the voltage of C6 and C8 and also
configured for input over voltage protection.
R7, C4 and D5 are formed the RCD to restrain
the high voltage spike to protect the MOSFET.
R15 is for switching frequency setup. Normally,
the switching frequency is configured low to get
good thermal performance under high voltage
input applications. And switching frequency
should be far away form data sampling frequency
in power meter applications to avoid noise
disturbing.
C11 is the power supply capacitor and C12 is the
decoupling ceramic cap to decouple the voltage
noise spike. C12 should be located near to IC.
R21, R22 are the sense resistors with 1%
tolerance for peak current setup.
C1, C3, C9 are the output filter capacitor to
restrain the output voltage ripple. One filter could
be used for strict voltage ripple requirement.
R1, R4 are dummy load to regulate the output
voltage within designed value.
R14, R17 are configured to set the output voltage.
U1, U3, R19 and C13 compose the control loop
to feedback the output signal to FB pin and
guarantee the quick control loop response and
system stability.
Input Line wire is connected to GND of main
output for input AC frequency sample in power
meter.
