AP1685MTR-G1 データシートの表示（PDF） - Diodes Incorporated.

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AP1685MTR-G1

OFFLINE, HIGH PF, HIGH EFFICIENCY LED DRIVER IC

Diodes Incorporated. 

A Product Line of

Diodes Incorporated

AP1685

Application Information

The AP1685 is designed for single voltage application, and it features high power factor correction (PFC), low total harmonic distortion (THD), low

BOM cost and good EMI performance. The device can be widely used in non-dimmable LED application such as GU10, bulb lamps, down lamp,

etc. The AP1685 adopts constant on time control method within one AC cycle to achieve the high power factor and low THD. The control scheme

is very simple, the power factor correction effectiveness is obvious, and the constant current control is also good enough.

L1

C1

F1

AC

VR1

Input

DB1

R9

C2

D2

R2

D1

R4

C3

R5

VCC FB

R1

RI

Drain

R6

S

GND CS

U1 AP1685

R7

R8

+

OUT

C4

T1

Figure 1. Typical Application Circuit

Design Parameters

Setting the Current Sense Resistor R8

As the AP1685 adopts constant on time control method, the current of the inductance will follow the input voltage to get a sinusoidal wave. The

current sense pin CS of the AP1685 will sense the peak current of the inductance by sensing the voltage dropped on the current sense resistor R8,

and the constant current control is realized by controlling the peak current. In buck structure, when the VO is higher than VIN, no energy will be

transferred from input to output which is called dead zone, and considering the dead zone of buck structure, the output current can be calculated

as below:

I o _ mean



k



1





Vcs_ ref

R8

Where,

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

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

So, the current sense resistor R8 is determined:

R8  k  V cs_ ref

  Io _ mean

Transformer Selection (T1)

The non-isolated buck circuit in Figure 1 is usually selected, and the system is operating at boundary conduction mode. The system’s operating

frequency does not keep constant, the minimum switching frequency at the crest is set as fmin, and then the buck inductance value L can be got:

(

L

2 Vin _ rms Vo )  R8 Vo

Vcs_ ref  2 Vin _ rms  f min

Where,

VO is the output voltage.

Vin_rms is the RMS value of the input voltage.

AP1685

Document number: DS37311 Rev. 1 - 2

8 of 14

www.diodes.com

September 2014

© Diodes Incorporated

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