PS2625 datasheet(17/38 Pages) NEC

17 / 38 page

Expression (6) indicates that the current transfer ratio (CTR) is significantly affected by the value of ICBL • RBE. For example, if

the forward current IF of the light-emitting diode is smaller (that is, ICBL is smaller) or if the base-emitter resistance RBE is smaller,

the reduction rate (rate of IC') becomes greater.

The above CTR reduction must be considered when inserting a resistor between the emitter and the base of the phototransistor

of the optocoupler to increase the switching speed. The performance of the optocoupler might become unstable because the

CTR will be affected by time elapse or temperature change (even if it is initially stable).

Fig. 3-3 shows the

∆CTR-RBE characteristics.

Normalized to 1.0

at RBE =

IF = 1 mA, VCE = 5V

CTR = 274%

CTR =166%

1.0

0.8

0.6

0.4

0.2

100

200

300 400 500

1000

Base Emitter Resistance RBE (k

Ω)

Base Emitter Resistance RBE (k

Ω)

Base Emitter Resistance RBE (k

Ω)

Figure 3-3.

∆CTR-RBE Characteristics

CTR = 274%

CTR =166%

1.0

0.8

0.6

0.4

0.2

100

200

300 400 500

1000

Normalized to 1.0

at RBE =

IF = 10 mA, VCE = 5V

CTR = 274%

CTR =166%

Normalized to 1.0

at RBE =

IF = 5 mA, VCE = 5V

1.0

0.8

0.6

0.4

0.2

100

200

300 400 500

1000

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