MP110 – 900V OFFLINE SWITCHING REGULATOR

reduce RMS current but increase transformer

usually between 0.8 and 1 for the universal input

range and 1 for a 230VAC input range.

Figure 8: Typical Primary-Current Waveform

For CCM at minimum input, the converter duty

cycle is:

OF

O

F

DC(min)

(V

V ) N

D

(V

V ) N

V

+×

=

+

×+

Where:

N is the transformer turns ratio.

The MOSFET turn-on time is

ON

S

D

T

f

=

The input average current, ripple current, peak

current and valley current of the primary side are

described as follows:

in

AV

DC(min)

P

I

V

=

ripple

P

peak

I

KI

=

×

AV

peak

P

I

I

K

(1

) D

2

=

−×

valley

P

peak

I

(1 K ) I

= −

×

DC(min)

ON

m

ripple

VT

L

I

×

=

Current-Sense Resistor

Figure 9: Slope Compensation waveform

Figure

9

shows

the

slope

compensation

waveform. When the sum of the sense resistor

voltage and the slope compensation voltage

off the internal MOSFET. The maximum peak

slope

compensation slew rate is

40mV/us.

peak current limit at full load. The voltage on

sense resistor is given by the following equation: .

sense

CS

Ramp

ON

V

0.95 V

S

T

=

×−

×

So the value of the sense resistor is

sense

sense

peak

V

R

I

=

Select the current sense resistor with appropriate

power rating based on the power loss:

(

)

2

2

peak

valley

sense

peak

valley

sense

II

1

P

I

I

DR

2

12





+







=

+

×

−

××













PRO pin

Extra protection can be enable thru the MP110

PRO pin. A typical input over-voltage protection

circuitry is shown in figure 10.

MP110 Rev. 1.01

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6/4/2014

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