NSI45090DDT4G

http://onsemi.com

5

Comparison of LED Circuit using CCR vs. Resistor Biasing

ON Semiconductor CCR Design

Resistor Biased Design

Constant brightness over full Supply Voltage

(more efficient), see Figure 10

Large variations in brightness over full Automotive Supply Voltage

Little variation of power in LEDs, see Figure 11

Large variations of current (power) in LEDs

Constant current extends LED strings lifetime, see Figure 10

High Supply Voltage/ Higher Current in LED strings limits lifetime

Current decreases as voltage increases, see Figure 10

Current increases as voltage increases

Current supplied to LED string decreases as temperature

increases (self-limiting), see Figure 2

LED current decreases as temperature increases

Single resistor is used for current select

Requires costly inventory

(need for several resistor values to match LED intensity)

Fewer components, less board space required

More components, more board space required

Surface mount component

Through-hole components

Figure 10. Series Circuit Current

Figure 11. LED Power

16

15

14

13

12

11

10

9

40

60

80

120

0

20

15

16

14

13

12

11

10

9

100

200

300

400

Circuit Current with

CCR Device

Circuit Current

with 83.3 W

Representative Test Data

for Figure 8 Circuit, Current

2 oz Copper Area

500

LED Power with

CCR Device

LED Power

with 83.3 W

Representative Test Data

for Figure 8 Circuit, Pd of

2 oz Copper Area

0

600

700

100

800

140

There are two methods to measure current regulation:

incoming inspection of a CCR where test times are a

minimum. (t < 300

is applicable for application verification where the CCR will

be operational for seconds, minutes, or even hours. ON

effect can be minimized during circuit design with the

correct selection of board material, metal trace size and

weight, for the operating current, voltage, board operating

Characteristics table).