With the continuous popularization and development of electronic devices, switching power supplies (SPS) play a crucial role in various applications. Switching power supplies, with their advantages of high efficiency, compact size, and light weight, are widely used in communication equipment, computers, home appliances, industrial control, and other fields. In the design and implementation of switching power supplies, optocouplers (Optocoupler) serve as a critical electronic component with an irreplaceable role. This article will delve into the function and importance of optocouplers in switching power supplies.

Switching power supplies utilize the rapid switching characteristics of switching elements (such as MOSFETs, IGBTs, etc.) to regulate input voltage through techniques like pulse width modulation (PWM), thereby generating a stable output voltage. Compared to traditional linear power supplies, switching power supplies offer higher energy conversion efficiency, effectively reducing energy loss, and can provide the same output power in a smaller form factor.

The operating principle of switching power supplies is relatively complex, involving multiple circuits and control stages. As one of the key components, optocouplers are primarily used to achieve electrical isolation and signal transmission.

As the demand for power supplies in modern electronic devices continues to grow, switching power supplies (SPS) have become the mainstream choice in power supply design due to their high efficiency, compact size, and lightweight advantages. In the design of switching power supplies, signal transmission and electrical isolation are critical, and optical isolators, as excellent electrical isolation components, are widely used in switching power supplies. This article will explore the working principle, application scenarios, advantages, and development trends of optical isolators in switching power supplies.

An optical isolator is a component that uses light signals for electrical isolation, typically consisting of a light-emitting diode (LED) and a photodetector (such as a phototransistor or photodiode). The primary function of an optical isolator is to achieve electrical isolation between the input and output circuits while transmitting control signals, thereby preventing high-voltage circuits from affecting low-voltage circuits.

The operation of an optocoupler is relatively simple. When an input signal activates the LED, the LED emits a light signal. This light signal propagates through a transparent medium (such as air or optical fiber) to the photodetector, which converts the light signal into an electrical signal and outputs it. This process achieves electrical isolation, effectively preventing high voltage from interfering with the control circuit.

A switching power supply is a power supply method that rapidly switches current and voltage using switching components (such as MOSFETs, IGBTs, etc.). Its operating principle involves controlling energy conversion by switching the conduction and cutoff of switching components, thereby achieving voltage regulation and power adjustment. Switching power supplies offer advantages such as high efficiency, compact size, and lightweight design, and are widely used in fields such as computers, communication equipment, and consumer electronics.

Optocouplers achieve electrical isolation between input and output circuits through an “electric-to-optical-to-electric” conversion mechanism, preventing high-voltage circuits from interfering with or damaging low-voltage control circuits. This isolation feature significantly enhances power supply safety and reliability, particularly critical in high-voltage differential scenarios (such as between the input and output terminals of a switching power supply). For example: Isolating high-power and low-power sections: Preventing high-power circuits from interfering with low-power control signals. ‌Protecting user safety: By isolating high-voltage outputs from low-voltage control circuits, the risk of electric shock is reduced. As a bridge for control signals, optocouplers convert low-voltage control signals (such as PWM signals) into optical signals transmitted to the high-voltage side, driving the switching actions of power devices (such as MOSFETs or IGBTs). Their advantages include: ‌Interference resistance: Optical signals are unaffected by electromagnetic noise, ensuring the accuracy of control signals. ‌Fast response: The high bandwidth characteristics of optocouplers support the high-frequency regulation requirements of switching power supplies.

In the feedback loop, optocouplers transmit sampled signals of output voltage or current to the control chip to achieve closed-loop regulation. For example: ‌Voltage feedback: By continuously monitoring the output and adjusting the PWM duty cycle, voltage stability is maintained. ‌Current limiting: In case of overcurrent, the optocoupler triggers a protection mechanism to cut off the output. Optocouplers act as a fast signal transmission medium in protection circuits, detecting abnormal conditions (overvoltage, overcurrent, etc.) and triggering protective actions: ‌Overvoltage protection: The optocoupler transmits fault signals to the control end, cutting off the power supply output.

‌Isolation from noise interference: Prevents false triggering of protective mechanisms. The introduction of optocouplers also enhances the overall performance of switching power supplies: Efficiency improvement: Reduces switching losses and optimizes energy conversion. Stability enhancement: Reduces output fluctuations through noise isolation and rapid feedback. Summary: Optocouplers integrate isolation, control, protection, and feedback in switching power supplies, making them core components for ensuring safe, stable, and efficient power supply operation. With technological advancements, their role will further expand into intelligent power management applications.

An optocoupler, also known as an optical isolator or optical coupler, is an electronic component that uses light as a medium to transmit electrical signals. Its core components include a light-emitting device (typically an infrared light-emitting diode, LED) and a light-receiving device (a photoresistor or photoconductive semiconductor), which are encapsulated within the same housing. When an electrical signal is applied to the input end, the light-emitting device emits light, and the light-receiving device converts this light into a photocurrent, which is then output through the output end. This process achieves the conversion from “electricity” to ‘light’ and back to “electricity.” Due to its compact size, long lifespan, contactless design, strong anti-interference capability, excellent insulation properties, and unidirectional signal transmission characteristics, the optocoupler has found widespread application in digital circuits.

The optocoupler, or optocoupler device, plays a crucial role in switching power supplies.

1. Signal isolation: In complex power systems, the input and output terminals may be at different potentials. Optocouplers utilize their unique structure to convert electrical signals into optical signals, effectively isolating the electrical signals at both ends of the power supply. This prevents noise interference and signal distortion, significantly enhancing the reliability and stability of the circuit.  

2. Signal Transmission: Another important function of optocouplers is to convert electrical signals at the input end into optical signals, which are then converted back into electrical signals via photodetectors for output. This process enables signal transmission across different potentials, ensuring accurate information flow within the power supply system.

3. Voltage Regulation: By precisely controlling the current at the input terminal of the optocoupler, the voltage at the output terminal can be accurately regulated. This function is particularly important in switching power supplies, as it ensures voltage stability in the circuit, thereby protecting subsequent circuit components from voltage fluctuations.

Working Principle of the Optocoupler

The working principle of the optocoupler is based on the photoelectric conversion effect, with its internal structure primarily consisting of a light-emitting diode (LED) and a phototransistor. When the LED receives a current, it emits light of a specific wavelength, which is then received by the phototransistor and converted into an electrical signal for output. This process completes the electrical-to-optical-to-electrical conversion, thereby achieving signal isolation and transmission.

In the context of a switching power supply, the operation of the optocoupler can be broken down into the following steps:

1. Signal input: The control signal from the power supply system is first transmitted to the LED of the optocoupler.

2. Photoelectric conversion: When the LED receives current, it emits light, which is then detected by the phototransistor and converted into an electrical signal.

3. Signal output: The converted electrical signal is transmitted from the optocoupler's output terminal, further controlling or regulating the operating state of the switching power supply.

Optocoupler feedback circuit

In switching power supplies, optocouplers are also frequently used in feedback circuits. A feedback circuit is a control system that detects the output voltage or current, compares it with a set value, and then adjusts the power supply's operating state based on the comparison result to maintain stable output voltage or current.

The primary role of the optocoupler in feedback circuits is to isolate and transmit feedback signals. Through the optocoupler, the feedback circuit can detect changes in output voltage or current in real-time and with high accuracy, and feed this information back to the control system, thereby achieving precise control over the power supply's output.

In summary, optocouplers play a crucial role in switching power supplies. It not only effectively isolates and transmits signals but also participates in voltage regulation and feedback control, thereby enhancing the stability and reliability of the power supply system. As technology continues to advance, the performance and application areas of optocouplers will also continue to expand and improve.

The Role of Optocouplers

Optocouplers, electronic components that transmit electrical signals using light as a medium, play a crucial role in digital circuits. Its functions encompass six key points, which we will explore in detail below.  

(1) Application in Logic Circuits  

Optocouplers play a vital role in logic circuits, utilizing their unique optoelectronic conversion functionality to perform logical processing of digital signals.  

(2) Application as Solid-State Switches  

Another important application of optocouplers is as solid-state switches, where their high sensitivity and long lifespan make them excel in switching circuits.

(3) Application in trigger circuits

In trigger circuits, optocouplers can respond quickly and trigger related circuits, achieving precise timing control.

(4) Application in pulse amplification circuits

Additionally, optocouplers are widely used in pulse amplification circuits, where their strong pulse amplification capabilities ensure stable signal transmission.

(5) Applications in Linear Circuits

Optocouplers also play a crucial role in linear circuits, where their high precision and stability enable outstanding performance in analog signal processing.

(6) Applications in Special Environments

Furthermore, optocouplers can operate reliably in special environments such as high temperatures, high humidity, or strong electromagnetic interference, demonstrating their superior reliability.