19

A design example of an optocoupler circuit that operates for at least ten years is shown below (using Fig. 3-3, 4-2 and 4-3). The

major causes of CTR reduction area as follows:

(From Fig. 3-3)

×)

(From Fig. 4-2)

CTR change with time (10 years, Ta = 60

°C)

40% down (with respect to initial value, 0 year)

(From Fig. 4-3)

CTR-relative-value vs. ambient-temperature characteristics

(Ta = 60

°C)

°C)

Considering the above characteristics and safety factor = 2 (twice margin), the recommended CTR is:

21.6 x 1.4 x 1.15 x 1.15 x 2 = 80%.................(15)

(Reference)

or more.

Normalized to CTR

test conditon

1.2

1.0

0.8

0.6

0.4

0.2

0

010

10

10

10

23

4

5

Time (Hr)

Figure 4-2. Change of CTR with

Time (PS2601)

°C)

Figure 4-3. CTR-Relative-Value vs.

Normalized to 100

1.2

1.0

0.8

0.6

0.4

0.2

0

-55 -40

-20

20

40

60

80

100

0