MP024-10

– PRIMARY-SIDE CC/CV REGULATOR

MP024-10 Rev.1.0

www.MonolithicPower.com

16

4/17/2017

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Constant Voltage (CV) Operation

In constant voltage (CV) mode, the MP024-10

detects

the

output

voltage

from

FB

and

generates the switching frequency to regulate

the output voltage.

To regulate the output voltage on the primary

side, FB uses a resistor divider to sample the

calculated with Equation (5):

aux

aux

O

D

s

N

V

(V

V )

N







(5)

secondary diode.

During the conduction time of the secondary

diode,

the

difference

between

the

output

voltage and the voltage on the secondary

current

flowing

through

the

diode.

To

compensate for the voltage drop difference, the

0V

Sampling Point

Sampling Point

Figure 5: Auxiliary Winding Voltage

The FB sampling time is able to be customized

with different resistor values connected to SS

(see

Figure

6).

See

the

Electrical

Characteristics table on page 5 for all available

choices for the sampling time. The entire

customization process is completed before

start-up and stored in a register, so it does not

have any influence on the normal operation.

SS

Figure 6: External Resistor for Sampling Time

Customization

The sampling should be chosen almost at the

end of the secondary diode conduction period

for accurate CV regulation.

Constant Current (CC) Operation

Figure

7

shows

the

secondary

current

waveforms.

0

T

Figure 7: Secondary Current Waveform

and the CC loop control function maintains a

fixed ratio between the secondary diode on time

limits the maximum duty of the secondary side

diode on time as shown in Equation (6):

ons

S Max

t

D

T





(6)

The relationship between the output constant-

shown in Equation (7):

ons

out

pks

pks

S Max

ons

offs

t

11

I

I

I D

2

t

t

2







(7)

When the secondary diode is turned on, the

peak current on the secondary side can be

calculated with Equation (8):

p

pks

PK

S

N

II

N



(8)

The output current regulation is shown in

Equation (9):

p

out

PK

S Max

S

N

1

I

I D

2N





(9)

For different applications with different kinds of

CP. If CP is connected with a capacitor directly

value of 0.4.