AP3968/69/70

Document number: DS36759 Rev. 2 - 2

7 of 15

www.diodes.com

December 2013

© Diodes Incorporated

AP3968/69/70

A Product Line of

Diodes Incorporated

Operation Description

+

C1

+

D1

C

FB

CS

GND

AP3968/69/70

Ns

Np

Iout

Vs

CPC

Q1

Figure 1. Simplified Flyback Converter Controlled by

AP3968/69/70

Figure 1 illustrates a simplified flyback converter controlled by AP3968/69/70.

Constant Primary Peak Current

The current rises up linearly at a rate of:

M

L

)

t

(

vg

dt

)

t

(

dip



Ip

0A

See equation 2

Figure 2. Primary Current Waveform

As illustrated in Figure 2, when the current Ip(t) rises up to Ipk, the switch Q1 turns off. The constant peak current is given by:

Rcs

Vcs

Ipk 

…………(2)

2

M

Ipk

L

2

1

Eg







…………(3)

So the power transferring from input to output is given by:

SW

2

M

f

Ipk

L

2

1

P







