PS2602 datasheet(15/38 Pages) NEC

15 / 38 page

NOTES ON USE OF OPTOCOUPLER BASE PIN

This chapter explains the reduction of a current transfer ratio of an optocoupler whose base and emitter are connected by a

resistor (RBE) and other optocouplers that seem to be significant in the treatment of the base pin of an optocoupler.

EQUIVALENT CIRCUIT (FOR PS2601 OPTOCOUPLER)

Fig. 3-1 shows an equivalent circuit of a single-transistor optocoupler such as the PS2601.

: Junction capacity of LED

CBE : Base-emitter capacitance

: Resistor serially connected to LED

ICBL : Collector-base photocurrent generated by the light of the LED

C1-2 : Input-output capacitance

: Amplifying transistor

DEFINITION OF CURRENT TRANSFER RATIO (CTR)

A current transfer ratio (CTR) of an optocoupler indicates the rate of an output current IC of its phototransistor to a forward input

current (IF) flowing through its light-emitting diode (LED). The CTR is expressed by:

CTR =

x = 100 (%) ................(2)

where IC = ICBL•hFE ..............................(3)

(hFE: D.C. current amplification factor of the phototransistor)

Figure 3-1. Equivalent Circuit (for PS2601 Optocoupler)

C1-2

CCB

CBE

ICBL

PS2602 Datasheet(PDF) 15 Page - NEC