AP1694A Datasheet, PDF (8/15 Pages) Diodes Incorporated – OFFLINE, HIGH PF, HIGH EFFICIENCY DIMMABLE LED DRIVER CONTROLLER

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AP1694A
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.
L1
L
RF
N
F1
BD1
C1
TVS1
R9
R2
C2
Z1
R3
D2
Q2
D1
R4
C3
VCC _FB
R1
RI
OUT
SGND
GND ^CS
U1 AP1694A
Q1
R7 _R8
+
C4
OUT
T1
R5
R6
Figure 1. Typical Buck Application Circuit
   When the dimmer is connected, and the conduction angle of the dimmer is
, according to the control principle of the IC, the output current
can be got as below:
I_o
(
,
)

1
2

I
pk
(
,
)

1

2
₀

V_{cs _ ref}
R8
sin( )
i（f 
else
 ）
In consider of the dead zone of the buck structure, the output current DC value can be calculated as below:
 ^{Io _ mean}

k¹


0 ^{Io (, )d}
Where,
V_{cs _ ref} is the reference of the current sense, and the typical value is 1V.
 is the cut off angle of dimmer.
 _{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 ), the output current DC value can be got as:
I_{o _ mean}

k
¹

 ^Vcs_ref
R8
AP1694A
Document number: DS37094 Rev. 1 - 2
8 of 15
www.diodes.com
May 2014
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