Industry news

2016August

How to design the LED constant current drive circuit design

From: www.szbako.com Data:02/08/2016

The basic circuit of


, the constant voltage power supply (

1

left) by feedback resistors

RFB1

and

RFB2

,

when the load current changes,

VFB

changes, "/p>

DC/DC

regulator by detecting the changes of

VFB

, the output voltage is maintained at a fixed level:

V0= (VFB* (RFB1+RFB2) /RFB1) (1)

in figure

1

right in the circuit,

DC/DC

regulator

FB

is the high impedance input current flows through the

IF

LED

:

IF=VFB/RFB (2)

graph

1

is

IF

with a constant,

DC/DC

regulator sensing

VFB

, then adjust the

LED

is The end voltage, so that the current flowing through the

LED

to remain constant. This is the use of

DC/DC

regulator

FB

feedback to achieve constant pressure to the principle of constant current conversion.

in general, the changes of

VFB

regulator

DC/DC

have a perception that once selected

LED

, the size of the current

IF

also is indeed

VFB

fall permitted in the regulator

DC/DC

.

to

VFB

equal to

1.25V

as an example, suppose

IF

respectively

15mA

,

350mA

and

700mA

, sampling resistor power dissipation will were less than

20mW

,

400mW

and

800mW

.

for

1W