Cirrus-logic AN374 Manual do Utilizador descarregar pdf (Página 22)

AN374

22 AN374REV2

Step 2) Translate into LED current profile at room temperature

The translation is as shown in Figure 13.

Variables K

and K

represent the luminous efficacy of the LED, and variables m

and m

are arbitrary

constants. The plot in Figure 13 illustrates the relationship between CCT and output currents, lumens, and

output power.

The data points 1, 2, and 3 are recreated under thermal equilibrium with the target LED light engine at room

temperature to obtain the LED current profiles for each channel across the entire range of the target lumen

output. The NTC temperature recorded on the final measurement is used on the driver. At the end of this

procedure, the following are obtained: the current versus dim, forward voltage versus dim, NTC resistance

versus dim, current ratio versus dim, and the LED light engine power profile data at room temperature.

Step 3) Validate data across various ambient temperatures

Finally, the same step needs to be completed across different ambient temperatures. All the measurements

should be performed when the system has reached thermal equilibrium. Once the data is taken, the sample

data is shown in Figures 14 and 15.

, I

Red

, m

, I

White

Red

/ I

White

Ratio of the 2

Channel’s Lumens

Sum of Each

Channel’s Lumens

Approximated

Using Current

Approximated

Using Current

0.02

650

1.0

0.02

2700

1600

Dim Dim Dim

1.0

0.02 1.0

0.02

Ratio

1.0

0.02 1.0

0.02

Ratio

1.0

, P

Red

+ K

, P

White

, P

Red

, P

White

Brightness (lm)

Relative Brightness (lm)

CCT (K)

Figure 13. Translate Data and CCT Lumen Dependence on Output Current

0.02

Red

(A)

Dim

1.0

amb

= 5°C

amb

= 25°C

amb

= 40°C

amb

= 55°C

Figure 14. Red Current Across Dim at Various Ambient Temperatures

1 2 ... 17 18 19 20 21 22 23 24 25 26 27 ... 34 35

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