AL1697

Document number: DS38223 Rev. 3 - 2

9 of 13

www.diodes.com

January 2016

© Diodes Incorporated

AL1697

Dimming Control

largest conduction angle, the device still has the adjustability to control the output current constant before COMP voltage is adjusted to the

maximum 4V, so for most of the dimmer, the output current is almost the same with the no dimmer condition at the largest conduction angle. If the

conduction angle is decreased, the COMP pin voltage will continue to increase quickly till to the maximum level (typical 4V), the device will output

resistor (R6).

we can get the following equation:

__

_

()

2

I N

RMS

ON

MAX

PEAK

DIM

V

Sin

t

I

L







From the buck-boost output current equation, we can get the output current when dimming:

_

_

_

0

_

1

25

()

2

( )

11

2

2

( )

REF

ON

ON

MAX

O

IN

RMS

PEAK

DI M

IN

RMS

O

V

if t

t

R

I

V

Sin

I

d

else

V

Sin

V













 





















Where,

Conduction Angle (deg)

Output Current (%)

100

0

180

Critical Conduction Angle



0

Figure 3. Dimming Curve

Dimmer Compatibility

Passive Bleeder Design

The passive bleeder is designed to supply latching and holding current to eliminate dimmer misfire and flicker.

DB1

C1

L1

R1

FR1

L

N

C2

Passive

Bleeder

Damping

Figure 4. LED Driver Schematic with Passive Bleeder