MP156 –SMALL, ENERGY-EFFICIENT, OFF-LINE REGULATOR

MP156 Rev. 1.14

www.MonolithicPower.com

13

4/21/2016

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Topology Options

MP156 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 DC input voltage

for the converter. Figure 7 shows the typical DC

bus voltage waveform of a half-wave rectifier.

Vin

DC input voltage

t

AC input voltage

Figure 7: Input Voltage Waveform

Typically, the use of a half-wave rectifier requires

an input capacitor rated at 3uF/W for the

universal input condition. When using the full-

wave rectifier, choose a smaller capacitor. Avoid

a minimum DC voltage below 70V; a low DC

input voltage can cause thermal shutdown.

Inductor

The MP156 has a minimum off-time limit that

determines the maximum power output. The

maximum power increases as the inductor

increases. Using a smaller inductor may cause

failure at full load, but a larger inductor means a

higher OLP load. For best results, select an

inductor with the minimum value that can supply

the rated power. Estimate the maximum power

with:

τ

omax

o peak

V

PV (I

)

2L

, for CCM

=⋅

τ

2

o max

peak

minoff

11

PLI

2

, for DCM

To account for different converter tolerances—

such as peak current limitation, minimum off time

maximum output power. Choose an inductor with

0

0.5

1

1.5

2

2.5

3

0.6

1.1

1.6

2.1

2.6

For a 1.2W converter (12V, 0.1A), the minimum

inductor value is about 0.9mH.

To reduce costs, use a standard off-the-shelf

inductor no less than the calculated value.

Freewheeling Diode

Select a diode with a maximum reverse voltage

rating greater than the maximum input voltage,

and a current rating determined by the output

current.

The freewheeling diode’s reverse recovery can

affect efficiency and circuit operation, so use an

ultra fast diode such as the EGC10JH.

Output Capacitor

The output capacitor is required to maintain the

DC output voltage. Estimate the output voltage

ripple as:

CCM _ ripple

ESR

so

i

Vi R

8f C

Δ

=+ Δ ⋅

, for CCM

2

pk

o

o

DCM _ ripple

pk

ESR

so

pk

II

I

VI

R

fC

I

⎛⎞

−

=⋅

+

⋅

⎜⎟

⎜⎟

⎝⎠

, for DCM