Introduction and Function of Photoelectric Sensors 

The photoelectric sensor achieves functions such as object detection and distance measurement through the emission, reflection or obstruction of light signals. It is widely used in industrial automation (production line counting), intelligent logistics (AGV navigation), security monitoring (infrared alarm), and other scenarios.

Principle of Photoelectric Sensor

A typical collimated type / diffuse reflection type photoelectric sensor, its core is the "light → electrical signal conversion circuit", combined with LED status indication and transistor-driven load (such as relays), and using the photoelectric effect to achieve the detection of physical quantities: 

1. Transmitting end: Generates optical signals (such as infrared LEDs, laser diodes); 

2. Receiver: The photosensitive components (such as photodiodes and phototransistors) convert the optical signal into an electrical signal; 

3. Signal processing circuit: Amplifies and shapes the electrical signal, and outputs it to the MCU or control system.

（Typical system block diagram of photoelectric sensor）

Design of Static Surge Protection Scheme

Lebao Electronics adopts the "categorized protection" strategy, establishing a protection system from the power supply end to the signal interface. 

Power supply end (brown wire + blue wire) protection 

· Risk: The 10-30V power supply is vulnerable to surge impacts (such as hundreds of volts of pulses induced by lightning strikes), which can directly damage the main circuit. 

· Leiditech's recommended solution: Connect a small-sized, high-power TVS diode SMBJ33CA in parallel between the brown wire and the blue wire: 

It covers a working range of 10 to 30V, leaving some margin. 

Peak pulse power (Pₚ): 400W (in accordance with the IEC 61000-4-5 standard surge test) 

Response time ≤ 1ns (fast clamping). 

(2) Protection of the signal output terminals (black line, orange line) 

· Risk: Static electricity at the load end (such as sparking at relay contacts) can reverse and invade, causing breakdown of the transistor collector. 

· Solution: In the area between the black line, orange line and blue line, small-volume ESD diodes SD36C (SOD323 ultra-small package) are paralleled to provide protection against electrostatic surge, covering a power supply voltage range of 10-30V, meeting IEC61000-4-2, level 4, contact discharge 30kV, and air discharge 30kV. 

(3) Protection of the input terminal (powder line) 

Solution: A small-sized ESD diode ESDA05CP30 is connected in parallel between the pink line control terminal and the blue line. This effectively protects the main control MCU and complies with IEC 61000-4-2, level 4, with a contact discharge of 30kV and an air discharge of 30kV.

Leiditech is committed to becoming a leading brand in electromagnetic compatibility solutions and component supply, offering products such as ESD, TVS, TSS, GDT, MOV, MOSFET, Zener, and inductors. Leiditech has an experienced R&D team that can provide personalized customization services based on customer needs, offering the best solutions to customers.