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Fabricante

MP156

Small, Energy-Efficient, Off-line Regulator 30mW No-Load Power Consumption

Monolithic Power Systems 

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

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

VDC(max)

DC input voltage

VDC(min)

AC input voltage

t

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:

Po max

=

Vo (Ipeak

−

Vo τmin off

2L

),

for

CCM

Po max

=

1

2

LIp2eak

⋅1

τmin off

,

for

DCM

To account for different converter tolerances—

such as peak current limitation, minimum off time

and so on—find the minimum value, Pmin, of the

maximum output power. Choose an inductor with

a Pmin higher than the rated power.

Figure 8 shows a example of a Pmin curve with a

12V output. (Ipeak=0.29A, τminoff=18μs)

3

2.5

2

1.5

PMIN

1

0.5

0

0.6 1.1 1.6 2.1 2.6

Figure 8: Pmin vs. L at 12V

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:

VCCM _ ripple

=

Δi

8fsCo

+ Δi ⋅ RESR ,

for

CCM

VDCM _ ripple

=

Io

fsCo

⋅

⎛

⎜⎜⎝

Ipk −

Ipk

Io

⎞2

⎟⎟⎠

+ Ipk

⋅ RESR

,

for

DCM

MP156 Rev. 1.14

www.MonolithicPower.com

13

4/21/2016

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© 2016 MPS. All Rights Reserved.

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