MP44019

– CRM/DCM MULTI-MODE PFC CONTROLLER WITH SECOND OVP

MP44019 Rev. 1.0

MonolithicPower.com

21

4/30/2021

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© 2021 MPS. All Rights Reserved.

The

minimum

boost

inductance

can

be

estimated with Equation (21):

AC_MAX

MIN

CS

OCP_OCL

2V

300ns

L

=

R

= 37.5 H

V



 (21)

Selecting the Boost MOSFET

The voltage rating of the MOSFET is determined

by the output voltage, over-voltage protection

(OVP) threshold, and a margin, such that VDS >

VO + ΔVOVP. The current rating of the MOSFET

is determined by the RMS value of the current

flowing through the MOSFET.

VDS can be calculated with Equation (22):

VDS > VOUT + ∆VOVP = 440V

(22)

The RMS current of MOSFET can be estimated

with Equation (23):

IQRMS=2√2×IAC_MAX×√

1

6

-

4√2

9π

×

VAC_MIN

VOUT

=3A (23)

In addition, the MOSFET pulse-drain current

should

exceed

the peak

inductor current,

calculated with Equation (24):

ID_PULSE > ILPK_MAX = 2√2×IAC_MAX = 8.6A (24)

Selecting the Boost Diode

The boost diode should have the same voltage

rating as the boost MOSFET.

The average current of the output diode is the

same as the output current of the PFC regulator,

calculated with Equation (25):

IDAVG = IOUT = 0.6A

(25)

To estimate the power consumption of the diode,

the RMS current can be calculated with Equation

(26):

IDRMS = 2√2×IAC_MAX×√

4√2

9π

×

VAC_MIN

VOUT

= 1.82A (26)

The boost diode must have an average and RMS

current ratings that exceed IDAVG and IDRMS,

respectively.

Diodes are available with a range of different

speed and recovery charges. Fast diodes

typically have higher conduction loss but lower

switching loss. Slow diodes typically have lower

conduction loss but higher switching loss.

Maximum efficiency is achieved when the diode

speed rating matches the application. In this

case, a boost diode with a fast recovery is

recommended.

Selecting the Output Capacitor

When selecting an output capacitor, consider the

output voltage ripple (VO_RIPPLE), ripple current

rating, and hold-up time.

The output ripple is a function of the effective

series resistance (ESR) of the capacitor, the

output voltage, and the line frequency (fLINE). The

output ripple can be estimated with Equation (27):

VO_RIPPLE = 2x

POUT

VOUT

x√

1

(

2π×2fLINExCOUT)2

+ESR

2

(27)

In this case, the calculated ripple with the

selected capacitor should be below 3% of the

output voltage, and the ESR of the output

capacitor is assumed to be 1

Ω. COUT can be

calculated with Equation (28):

COUT ≥

1

2πx2fLINE√(

3%×VOUT

2

2xPOUT

)

2

-ESR2

= 160μF

(28)

To ensure that the error amplifier

’s nonlinear

gain is not activated by the extremes of the

output voltage ripple, the output voltage ripple

amplitude should satisfy the condition calculated

with Equation (29):

VO_RIPPLE

VOUT

≤

2x100mV

VR

= 8%

(29)

The maximum RMS ripple current flowing in the

output capacitor can be estimated with Equation

(30):

IO_RIPPLE_MAX =√IDRMS

2

- (

POUT

VOUT

)

2

= 1.72A

(30)

This current flowing into the output capacitor is

made up of a switching frequency component

(50Hz)

and

a

twice-line

frequency

ripple

component (100kHz), calculated with Equation

(31) and Equation (32), respectively:

IO_RIPPLE_50Hz =

1

√2

x

POUT

VOUT

= 0.424A

(31)

IO_RIPPLE_100KHz =√IDRMS

2

-

3

2

x (

POUT

VOUT

)

2

= 1.67A (32)