MP161 – INTEGRATED POWER SOLUTION FOR HOME/INDUSTRIAL AUTOMATION
Estimate the OLP point for CCM with Equation
(4):
APPLICATION INFORMATION
Selecting the Input Capacitor
Vominoff
The input capacitor supplies DC input voltage to
the converter. Figure 5 shows the typical DC
bus voltage waveform of the half-wave rectifier
and full-wave rectifier.
P
Vo(ILimit
)
(4)
omax
2L
Estimate the OLP point for DCM with Equation
(5):
VDC(max)
Vin
1
1
DC input voltage
P
LIL2imit
(5)
omax
2
minoff
VDC(min)
To reduce costs, use a standard off-the-shelf
inductor no less than the calculated value.
AC input voltage
t
Selecting the Freewheeling Diode
VDC(max)
Vin
The diode should be selected based on the
maximum input voltage and peak current.
DC input voltage
AC input voltage
The freewheeling diode’s reverse recovery can
affect efficiency and circuit operation for CCM.
Use an ultra-fast reverse recovery diode, such
as the UGC10JH.
VDC( min)
t
Figure 5: Input Voltage Waveform
Selecting the Output Capacitor
An output capacitor is required to maintain the
DC output voltage. Estimate the output voltage
ripple for CCM with Equation (6):
Typically, the use of a half-wave rectifier
requires an input capacitor rated at 3µF/W for
the universal input condition. When using a full-
wave rectifier, the input capacitor is rated at 1.5
~ 2µF/W for the universal input condition. The
half-wave rectifier is recommended for <2W
output applications. The full-wave rectifier is
recommended for >2W output applications.
i
8fsCo
VOUT _ripple
iRESR
(6)
Estimate the output voltage ripple for DCM with
Equation (7):
Avoid using an input capacitor that is too small,
since it may not be able to hold the DC voltage
high enough. A low DC input voltage can lead
to bad thermal performance. If the input voltage
is very low, the MOSFET on time may reach
Tmaxon, triggering brown-out protection.
2
Ipk I
Io
o
(7)
VOUT _ripple
IpkRESR
fsCo
Ipk
Low ESR electrolytic or ceramic capacitors are
recommended to reduce the output voltage
ripple if necessary.
Selecting the Inductor
External Feedback Resistors
The MP161 has a minimum off-time limit that
determines the maximum output power. The
maximum power increases as the inductor
increases. Using a very small inductor may
cause not enough output power, but a larger
inductor leads to an inappropriate OLP point.
Select an inductor with a minimum value that
can meet the overload requirement. The
tolerance of the peak-current limit and minimum
off time should also be considered for mass
production.
For adjustable output configurations, the total
external resistance should not exceed 100kΩ to
override the internal feedback resistor divider.
The external resistor value can also be adjusted
to meet the output voltage target if large
external resistors are preferred.
MP161 Rev. 1.0
8/4/2017
www.MonolithicPower.com
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