MP163 – 700V, NON-ISOLATED, OFFLINE REGULATOR WITH INTEGRATED LDO

MP163 Rev. 1.01

www.MonolithicPower.com

17

8/11/2017

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Feedback Capacitor

The feedback capacitor provides a sample

hold function. Small capacitors result in poor

regulation at light loads, and large capacitors

affect the circuit operation. Roughly estimate an

optimal capacitor value using Equation (11):

oo

o

o

FB

12

o

1

2

o

VC

VC

1

C

2R

R

I

R

R

I









(11)

Dummy Load

A dummy load is required to maintain the load

regulation. This ensures sufficient inductor

energy

to

charge

the

sample

capacitor to detect the output voltage. Normally

,

a 3mA dummy load is needed and can be

adjusted according to the regulated voltage.

There is a compromise between small, no-load

consumption and good, no-load regulation,

especially for applications that require 30mW

of

no-load consumption. Use a

reduce

regulation is not a concern.

Auxiliary VCC Supply

For

above 7V,

an external VCC supply to reduce overall power

consumption (see Figure 7).

Figure 7: Auxiliary VCC Supply Circuit

This auxiliary VCC supply is derived from the

resistor connected between C3 and C4. C4

should be larger than the value recommended

above. D3 is used in case

with FB. R3 is determined

OUT

FW

S

VV

5.8V

R3

I





(12)

applications, R3 should be adjusted to meet the

application’s

specific

In

a

particular

Surge Performance

An appropriate input capacitor value should be

chosen to obtain

Figure 8 shows the half-wave rectifier. Table

1

shows the capacitance required under normal

conditions for different surge voltages. FR1 is a

20Ω/2W fused resistor, and L1 is 1mH for this

recommendation.

L1

C1

C2

N

L

FR1

Figure 8: Half-Wave Rectifier

Table 1: Recommended Capacitance

Surge

Voltage

500V

1000V

2000V

C1

1μF

2.2μF

3.3μF

C2

1μF

2.2μF

3.3μF