MP157 –SMALLEST ENERGY EFFICIENT OFF-LINE REGULATOR WITH EXTENDED POWER RANGE

MP157 Rev. 1.04

www.MonolithicPower.com

15

6/27/2016

MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.

© 2016 MPS. All Rights Reserved.

Topology Options

MP157 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 is used to supply the DC

input voltage for the converter. Figure 7 shows

the typical DC bus voltage waveform with half-

wave rectifier and full-wave rectifier.

Vin

DC input Voltage

a) DC input with half-wave rectifier

Vin

DC input Voltage

b) DC input with full-wave rectifier

Figure 7: Input voltage waveform

When the half-wave rectifier is used, the input

capacitor is usually set as 3uF/W for the

universal input condition. And when the full-wave

rectifier is used, we could choose a smaller

capacitor usually set as 1.5-2uF/W. Avoid the

minimum DC voltage below 70V. Low DC input

voltage will bring the problem of thermal

shutdown. Half-wave rectifier is recommended

for <2W output application and full-wave rectifier

is recommended for >2W output application.

Inductor

MP157 has a minimum off time limit, and this

decides the maximum power it can output. The

maximum power increases as the inductor

increases. Using a smaller inductor may fail

output the full load. The maximum power can be

obtained as:

omin off

omax

o peak

Vt

PV (I

)

2L



, For CCM





2

o max

peak

min off

11

PLI

2

, for DCM

To consider the parameter error of the converter

such as peak current limit, minimum off time and

so on, we can obtain the minimum value Pmin of

the maximum power. The principle of choosing

the inductor is that Pmin should be higher than

the rated power.

Take the output voltage 12V as examples, the

curve of Pmin for 12V is shown as Figure 8,

(Ipeak=0.64A, tminoff=13.1

s)

INDUCTANCE(mH)

2.6

3

3.4

3.8

4.2

4.6

5

0.4

0.5

0.6

0.7

0.8

0.9

Figure 8: Pmin vs. L at 12V output

For CCM operation, the selection of L should

make the frequency of converter lower than

40kHz to reduce the turn-on switching loss cause

by reverse recovery of free-wheeling diode at

high line input.

Freewheeling Diode

The diode should have a maximum reverse

voltage rating which is greater than the maximum

input voltage, and the current rating of the diode

is determined by the output current.

The reverse recovery of freewheeling diode can

affect the efficiency and the circuit operation. For

CCM operation. ultra fast diode with Trr<35ns is

used such as STTH2R06, STTH1R06, and

UGC10JH. For DCM operation, diode with

Trr<75ns is used.