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8.1.2 Open Collector Method
• NPN type (N type)
NPN type uses an NPN transistor at the output and when the transistor is turned ON, load current flows inward. Also
referred to as 'SINK type'.
The 2 external connection methods have been marked in figure 8-2. The first is when the NPN output provides a
passage to the load current. The other end of the load must be connected to the (+) voltage. This is also the case
when the solenoid valve is turned ON/OFF using the NPN output.
The other is when the NPN outlet is connected to the (+) voltage of an external input with pull-up resistor and delivers
the ON/OFF signal of the outlet. In this case, the (+) voltage level can be changed according to the pull-up power. This
method is usually used to connect open collector type sensors.
Figure 8-2. NPN output method connection
• PNP type (P type)
The PNP type uses an PNP transistor at the output and when the transistor is turned ON, load current flows in. Also
referred to as 'SOURCE TYPE'.
Figure 8-3 is a PNP output connection method. The NPN output supplies the current towards the load current. The
other end of the load must be connected to the ground. It is mostly used to turn ON/OFF the power supply of a load
circuit like LED.
Figure 8-3. PNP output method connection
