PS2625 datasheet(27/38 Pages) NEC

27 / 38 page

Standard characteristics

VCE = 5V

600

500

400

300

200

100

0.1

0.5

Sample A

Sample B

Forward Current IF (mA)

Figure 9. CTR vs. IF Characteristics (Standard Value)

Response Characteristics

The response characteristics of optocouplers are the same as those phototransistors. The fall time tf is expressed by:

tf RL•hFE•CCB

RL: Load resistance

hFE: Amplification factor

CCB: Collector-base capacitance

If RL is too high, tf becomes too high to be fit for high-speed signal transmission. Select the proper load resistance for the desired

signal rate. Similarly, the collector current must fully satisfy the minimum value of the CTR, CTR vs. TA characteristics, and CTR

vs. time characteristics. Otherwise, the phototransistor will operate unsaturated, causing lower response characteristics and

malfunction.

Figures 10 to 13 show the response-time vs. forward current characteristics and response-time vs. VCC characteristics, using load

resistance and ambient temperature as parameters.

CTR vs. IF Characteristics (IF: Forward Current Flowing Through the LED)

The current transfer ratio (CTR) depends upon the magnitude of a forward current (IF). When IF goes lower or higher than a

proper magnitude, the CTR becomes smaller. Figure 9 shows the CTR vs. IF characteristics.

Note that rate changes of CTRs are very diffrent at low IF magnitude (approx. 5 mA), middle IF magnitude (approx. 5 mA), and

high IF magnitude (approx. 20 mA). Namely, the CTR depends heavily upon the magnitude of forward current IF in lower and

higher current ranges.

For low-input and high-output switching, see Chapter 4.

PS2625 Datasheet(PDF) 27 Page - NEC