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6-3. Solid State Switching Components
Optical Switches
There are two types of optical switches: phototransistors and optocouplers. Phototransistors can
be used in two modes depending on the application. It can be used as either a light activated
transistor or as a light activated diode. In either mode, light is used to turn it on and allow current
to flow.
The optocoupler consists of a light emitting diode and a phototransistor in the same package.
They are electrically isolated. When the diode is turned on by an external signal, it radiates light.
This light falls on the phototransistor base junction that results in the device turning on.
Optocoupler Dynamic Testing
The Tracker 2700’s DC Source can perform a dynamic test of optocouplers. Apply the DC
Source's output to the control input of a switching device and connect Tracker 2700's test leads
across the component's switch terminals. Observe the optocoupler's signature for on and off
states.
Figure 6-33. Diagram of an Optocoupler
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