MP150 – OFFLINE PRIMARY-SIDE REGULATOR
MP150 Rev. 1.15 www.MonolithicPower.com 13
9/25/2018 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2018 MPS. All Rights Reserved.
Topology Options
MP150 can be used in common topologies, such
as Buck, Buck-Boost, Boost and Flyback. Please
find the Table.1 for more information.
Component Selection
Input Capacitor
The input capacitor supplies the converter’s DC
input voltage. Figure 7 shows the typical half-
wave rectifier’s DC bus voltage waveform.
Figure 7: Input Voltage Waveform
When using the half-wave rectifier, set the input
capacitor 3µF/W for the universal input condition.
When using the full-wave rectifier, choose a
smaller capacitor, but avoid a minimum DC
voltage below 70V to avoid thermal shutdown.
Inductor
MP150 has a minimum OFF time limit that
determines the maximum power output. The
maximum power increases with the inductor
value. Using a smaller inductor may cause the
output to fail at full load, but a larger inductor
results in a higher OLP load. The optimal
inductor value is the smallest that can supply the
rated power. The maximum power is:
ominoff
omax o peak
V
PV(I )
2L
, for CCM
2
omax peak
minoff
11
PLI
2
, for DCM
To account for converter parameters—such as
peak current limit and minimum OFF time—
estimate the minimum inductor power (P
min
) for
the maximum power, and selecting an inductor
with a P
min
value that exceeds the rated power.
Using output voltages 5V and 12V as examples,
Figure 8 shows the curve for P
min
at 5V, and
Figure 9 shows the curve for P
min
at 12V.
(I
peak
=0.29A, τ
minoff
=18µs).
MAXIMUM OUTPUT POWER(W)
INDUCTOR(mH)
0.6
0.7
0.8
0.9
1
1.1
1.2
0.6 1.1 1.6 2.1 2.6
P
MIN
Figure 8: P
min
vs. L at 5V
MAXIMUM OUTPUT POWER(W)
INDUCTOR(mH)
0.6 1.1 1.6 2.1 2.6
0
0.5
1
1.5
2
2.5
3
P
MIN
Figure 9: P
min
vs. L at 12V
When designing a 0.5W converter (5V, 0.1A),
estimate the minimum inductor value at 0.6mH
based on Figure 8. Similarly, for a 1.2W
converter (12V, 0.1A), estimate the minimum
inductor at 0.9mH based on Figure 9.
Use a standard off-the-shelf inductor to reduce
costs. Use a standard inductance that exceeds
calculated inductance.
Freewheeling Diode
Choose a diode with a maximum reverse voltage
rating that exceeds the maximum input voltage,
and a current rating that exceeds the output
current.
The reverse recovery of the freewheeling diode
can affect the efficiency and circuit operation.
Select an ultra-fast diode, such as the EGC10JH
for DCM and the UGC10JH for CCM.
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