AP3983R

Document number: DS38247 Rev. 3 - 2

9 of 15

www.diodes.com

June 2016

© Diodes Incorporated

AP3983R

0V

See equation 5

Figure 3 Auxiliary Voltage Waveform

The voltage detection point is at a constant delay time of the D1 on-time. The constant delay time is changed with the different primary peak

current. The CV loop control function of the AP3983R then generates a D1 off-time to regulate the output voltage.

Constant Current Operation

The AP3983R can work in constant-current (CC) mode. Figure 2 shows the secondary current waveforms.

fixed proportion is:

4

4



OFFS

ONS

t

t

(6)

The relationship between the output constant-current and secondary peak current Ipks is given by:

OFFS

ONS

ONS

PKS

MAX

O

t

t

t

I

I









2

1

)

(

(7)

As to tight coupled primary and secondary winding, the secondary peak current is:

PK

S

P

PKS

I

N

N

I





(8)

Thus the output constant-current is given by:

PK

S

P

OFFS

ONS

ONS

PK

S

P

MAX

O

I

N

N

t

t

t

I

N

N

I

















8

2

2

1

)

(

(9)

Therefore, the AP3983R can realize CC mode operation by constant primary peak current and fixed diode conduction duty cycle.

Multiple Segment Constant Peak Current

As to the original PFM PSR system, the switching frequency decreases with output current decreasing, which will encounter audible noise issue

since switching frequency decreases to audio frequency range, about less than 20kHz.

In order to avoid audible noise issue, the AP3983R uses 2-segment constant primary peak current control method. At constant voltage mode,