The difference between NPN and PNP photoelectric switches lies in their output levels. NPN outputs a low level, while PNP outputs a high level. The type of photoelectric switch is a highly specialized technical issue. What are NPN and PNP photoelectric switches? What are their differences?
1. Difference between NPN and PNP photoelectric switches
Photoelectric sensors have two output types: NPN output type (current inflow) and PNP output type (current outflow). When the current-outflow sensor (PNP output type) is connected, current flows from the power supply through the sensor's output terminal to the load and then to the ground terminal. (When the NPN sensor is connected, current flows from the power supply through the load to the sensor output, then to the ground terminal (GND), and finally to the system ground terminal.) PNP and NPN sensors typically have three output lines: the power supply line VCC, GND, and the OUT signal output line. 1. NPN type: NPN means that when a signal is triggered, the signal output line OUT and GND are connected, which is equivalent to OUT outputting a low level.
2. PNP type: PNP means that when a signal is triggered, the signal output line OUT is connected to VCC, which is equivalent to outputting a high-level power supply line OUT.
An NPN type photoelectric switch means that when a signal is triggered, connecting the signal output line OUT to the 0V line is equivalent to outputting a low level of 0V. For the NPN-NO type, when there is no signal trigger, the output line is paused, meaning the 0V line and OUT line are disconnected. When a signal trigger is present, it outputs the same voltage as the 0V signal trigger, meaning the OUT line is connected to the 0V line, resulting in a low level of 0V. For the NPN-NC type, when there is no signal trigger, it outputs the same voltage as the 0V line, meaning the OUT line is connected to the 0V line, resulting in a low level of 0V. When a trigger signal is received, the output line pauses, meaning the 0V line and OUT line are disconnected, similar to the NPN-NC+NO type. Adding an output line OUT allows for the selection of two output lines with opposite signals as needed.
3. PNP type photoelectric switch
A PNP photoelectric switch is a switch where, when a signal is triggered, the signal output line OUT is connected to the power supply line VCC, equivalent to a high-level power supply output. It is used for high-level power supply lines. For the PNP-NO type, the output line pauses when no signal is triggered, meaning the VCC power supply line and OUT are disconnected. When a signal is triggered, it sends a signal. The voltage of the VCC power supply line is the same, meaning the OUT line is connected to the VCC power supply line, outputting a high-level VCC. For the PNP-NC type, the voltage of the VCC power supply line is the same; without a signal trigger, the OUT line is connected to the VCC power supply line, outputting a high-level VCC. When a trigger signal is received, the output line pauses, meaning the VCC power supply line and OUT line are disconnected. The PNP-NC+NO is essentially another output line OUT, which can be selected as needed.
What are NPN and PNP photoelectric switches? What are their differences? PNP photoelectric switches have a lower pilot voltage and lower reverse withstand voltage; NPN photoelectric switches have a larger pilot voltage drop but higher reverse withstand voltage. If the input is high and the output needs to be low, choose NPN; if the input is low and the output needs to be low, choose PNP; if the input is low and the output needs to be high, choose NPN; if the input is high and the output requires a high level, choose PNP. With NPN, a high base voltage results in a short circuit between the electrode and emitter; with NPN, a low base voltage results in an open circuit between the electrode and emitter, meaning it doesn't work. With PNP, a high base voltage results in an open circuit between the electrode and emitter, meaning it doesn't work; if the base is high voltage, a low potential is applied to the PNP base, short-circuiting the collector and emitter. We commonly use NPN photoelectric switches, i.e., low-level active state; PNP is rarely used.
