AP1694A

Document number: DS37094 Rev. 1 - 2

8 of 15

www.diodes.com

May 2014

© Diodes Incorporated

AP1694A

A Product Line of

Diodes Incorporated

Application Information Based on Buck Structure

The AP1694A uses constant on time control method within one AC cycle to achieve the high power factor. When the dimmer is connected to the

driver, although a part of input voltage is cut off by the dimmer, the system still operates as constant on time mode, in this way good dimmer

compatibility can be realized.

T1

OUT

+

VCC

FB

OUT

CS

GND

U1 AP1694A

C3

R7

R5

R6

R4

D1

C4

R3

Q1

BD1

C1

L1

R8

D2

R1

RI

SGND

R2

R9

RF

L

N

C2

Z1

Q2

F1

TVS1

Figure 1. Typical Buck Application Circuit

When the dimmer is connected, and the conduction angle of the dimmer is



can be got as below:

_

1

sin( )

1

( , )

( , )

28

2

0

cs ref

o

pk

V

if

II

R

else



 

 

 











 

 



（

）

In consider of the dead zone of the buck structure, the output current DC value can be calculated as below:

_

0

1

( , )

o mean

o

I

k

I

d



  







Where,

_

cs ref

V

is the reference of the current sense, and the typical value is 1V.



is the phase of the input voltage.

k is the current modification coefficient , and the value is approximate to be 0.7.

When no dimmer is connected with the driver (

0

s_ref

_

1

8

c

o mean

V

Ik

R



  