AP1695

Document number: DS37312 Rev. 1 - 2

8 of 15

www.diodes.com

June 2014

© Diodes Incorporated

AP1695

A Product Line of

Diodes Incorporated

Application Information Based on Buck Structure

The AP1695 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.

VCC

RI

GND

S

Drain

FB

L

N

RF

BD1

ZD1

L1

C1

C2

R6

R4

R5

R1

R7

R8

T1

U1

C3

F1

TVS1

LED+

LED-

D2

R10

C4

+

R9

R2

R3

D1

Q2

5

4

1

7

6

CS

2

3

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



  