AN2946 datasheet(17/38 Pages) STMICROELECTRONICS

Part #	AN2946

Description	Solar-LED streetlight controller with 25 W LED lamp driver

PDF	38 Pages

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Manufacturer	STMICROELECTRONICS [STMicroelectronics]

Direct Link	http://www.st.com

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17 / 38 page

AN2946

Hardware design

Doc ID 15473 Rev 2

17/38

Figure 17.

V-I curve and PSC

According to Equation 1 and Equation 2, the maximum power point (MPP) occurs at

Usc = 0.5 × Udc. A different R value results in different output power at the MPP delivered to

the charger. From Table 2 as long as Udc is 36 V, Usc is kept at18 V no matter what the R

value is. Table 3 shows the result with fixed R and variable Udc. Usc is always half of Udc

during steady state. Thus the test diagram shows the way to find the MPP during the test.

Table 2.

Test results for different values of R (Vdc = 36 V)

Ω]

Usc [V]

Isc [A]

Uba [V]

Iba [A]

Charger

efficiency [%]

4.6

18.0

3.90

13.08

5.03

93.7

5.2

18.0

3.45

13.08

4.41

94.0

6.0

18.0

3.00

13.03

3.88

93.6

7.1

18.0

2.53

12.81

3.31

93.1

8.8

18.0

2.05

12.54

2.76

93.8

11.6

18.0

1.55

12.34

2.10

92.9

17.3

18.0

1.04

12.07

1.43

92.2

34.0

18.0

0.53

11.96

0.69

86.5

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