8

STABILIZING OUTPUT LEVELS

current. The current is amplified as a collector current and could make the output level of the phototransistor unstable. To

PS2603) 2601

Solid line: PS2601

Dotted line: PS2603

10000

Ω

Ω

1000

100

10

1

0.1

- 20

0

20

40

60

80

100

Ω

°C)

ELIMINATION OF INDUCED NOISE

Generally, machine-controlling equipment generates induced noise which may cause malfunctions. This unwanted noise in input

signals can be isolated by means of optocouplers. However, if the noise is too strong, it may be switched to the output through

Insert a capacitor (preferably 100 pF) between the base and the emitter of the phototransistor of the optocoupler. This capacitor

delays response and suppresses malfunctions.

Graph 6-(a) to 6-(d) show how an external noise (surge voltage of 1000 V/

µs at rise time) is eliminated as the capacitance of the

base-emitter capacitor.

A fluctuation in the collector-emitter voltage caused by the on/off operation of a power switch at the output of the optocoupler

if an input signal was applied to the optocoupler. Graph 7-(a) shows the waveforms. This unwanted instantaneous induction

Figure 2-6.

Figure 2-7.