PS2621 datasheet(20/38 Pages) NEC

20 / 38 page

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)

CTR-relative-value vs. RBE characteristics

15% down (with respect to initial value, RBE =

×)

(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)

15% down (with respect to initial value ta = 25

°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)

Accordingly, the CTR value including reduction of CTR by time elapse, temperature change, and insertion of RBE must be 21.6 %

or more.

IF = 5 mA

TA = 25˚C

IF = 20 mA

TA = 25˚C

IF = 5 mA

TA = 60˚C

Normalized to CTR

test conditon

IF = 5 mA, VCE = 5V

1.2

1.0

0.8

0.6

0.4

0.2

010

Time (Hr)

Figure 4-2. Change of CTR with

Time (PS2601)

Ambient Temperature TA (

°C)

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

TA Characteristics

Normalized to 100

at TA = 25˚C

IF = 5 mA, VCE = 5 V

1.2

1.0

0.8

0.6

0.4

0.2

-55 -40

-20

100

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