AL1696

Document number: DS38304 Rev. 1 - 2

10 of 14

www.diodes.com

October 2015

© Diodes Incorporated

AL1696

2

2

PEAK

L

em

LI

N

AB







Where,

In order to get a high power factor and good dimmer compatibility, the system should operate in constant on time mode at valley of input voltage. It

can be realized by setting the maximum on time, which is set by on external resistor connect to RT pin.

_

_

25

6

REF

ON

MAX

RT

REF

CR

t

V





Where,

Dimmer Compatibility

Passive Bleeder Design

The passive bleeder is designed to supply latching and holding current to get rid of dimmer

’s misfire and flicker.

DB1

C1

L1

R1

FR1

L

N

C2

Passive

Bleeder

Damping

DB1

Figure 2. LED Driver Schematic with Passive Bleeder

The passive bleeder includes a capacitor (C2, in hundreds of nF) to provide latching current and a resistor (R1) to limit the current spike. Because

a large C2 will affect the PF, THD and efficiency negatively, the value of the capacitor (C2) should be selected carefully. Generally, a capacitance

from 100nF/400V to 330nF/400V is recommended. R1 is used to limit the latching current. If R1 is too big, the latching current will be not enough

and the TRIAC dimmer will be misfired, resulting in LED flicker. If R1 is too small, it will result in greater power dissipation. Generally

, a 200Ω to

2KΩ resistor is recommended for R1.

Passive Damping Design

FR1 is to limit the spike current caused by quick charging of C2 when dimmer on. Normally, FR1 will be chosen

from 20Ω to 100Ω for low line like