A switching power supply is short for a switching regulated power supply. It generally refers to an AC-DC converter that takes AC voltage as input and outputs DC voltage. The power switching transistors inside a switching power supply operate in a high-frequency switching state, consuming very little energy. The power supply efficiency can reach 75%~90%, which is twice that of a conventional linear regulated power supply (linear power supply).
Switching power supplies are a widely used type of power supply in modern electronic devices, characterized by high-efficiency conversion and stable output. Optocouplers, as photoelectric conversion devices, play a crucial role in switching power supplies. This article from Advanced Opto Semiconductors will introduce the basic principles and specific applications of optocouplers in switching power supplies, as well as their significant contributions to the safety and stability of the power supply.
An optocoupler is a device composed of a photodiode and input/output circuitry. In switching power supplies, the basic principle of an optocoupler is to convert the electrical signal from the input circuit into an optical signal using a photodiode, and then use the optical signal to control the operating state of the output circuit. This photoelectric conversion method can achieve functions such as circuit isolation, voltage transformation, and current amplification, thereby improving the stability and safety of the power supply.
1. Application of optocouplers in switching power supplies
Electrical isolation: Optocouplers play a crucial role in electrical isolation within switching power supplies. By isolating the input and output circuits through optical signals, interference and damage from high-voltage circuits to low-voltage circuits can be effectively prevented. This isolation improves the reliability and safety of the power supply, protecting users and equipment.
Control Switch: Optocouplers also serve as important control switches in switching power supplies. By inputting optical signals, the switching state of the power supply can be controlled, achieving precise control of the power output. This control method improves the power supply's response speed and stability, adapting to the operating requirements under different load conditions.
Feedback control: Switching power supplies typically require a feedback mechanism to stabilize the output voltage. Optocouplers can be used to isolate and transmit feedback signals, ensuring their accuracy and stability. This feedback control allows the switching power supply to maintain a stable output voltage under varying input voltage and load conditions, meeting diverse application requirements.
2. The significant contribution of optocouplers to switching power supplies
Enhanced safety: Through electrical isolation, optocouplers protect low-voltage circuits from interference and damage from high-voltage circuits, reducing the risk of power failures and fires, and improving power supply safety.
Enhanced stability: The application of optocouplers in control switching and feedback control enables switching power supplies to maintain a stable output voltage under different load conditions. This stability improves the power supply's efficiency and reliability, and reduces the impact of power supply noise and fluctuations on equipment.
Achieving high-efficiency conversion: Optocouplers have high photoelectric conversion efficiency, enabling efficient power conversion and transmission. This improves the energy utilization rate of switching power supplies, reduces energy consumption and waste, and meets the requirements of energy conservation and environmental protection.
An optocoupler transmits electrical signals using light as a medium. The input electrical signal drives a light-emitting diode (LED) to emit light of a specific wavelength, which is then received by a photodetector to generate a photocurrent. This photocurrent is then amplified and output. This completes the electro-optical-electro-electrical conversion, thus achieving the functions of input, output, and isolation.
In switching power supply circuits, the main function of optocouplers is to achieve photoelectric conversion and isolation, thus preventing mutual interference between input and output.
The role of optocouplers varies in different switching power supply designs. In general isolated power supplies, optocoupler isolation feedback is a simple and low-cost method. However, in many cases, insufficient understanding of the working principle of optocouplers and improper optocoupler connections can lead to circuit malfunctions.
When designing an optocoupler in a switching power supply circuit, the following principles must be followed:
1. Select an optocoupler that conforms to relevant domestic and international standards for isolation breakdown voltage, based on the isolation withstand voltage between the product's input and output.
Second, linear optocouplers should be preferred because the CTR value has good linear adjustment within a certain range.
2. The ideal range for the current transfer ratio (CTR) is 50% to 200%. This is because when the CTR is too low, the LED in the optocoupler requires a larger operating current, which increases the optocoupler's power consumption; when the CTR is too high, it may affect normal output during circuit startup or sudden load changes.
In a switching power supply circuit, the optocoupler is powered by the secondary voltage of a high-frequency transformer. When the output voltage is lower than the voltage of the Zener diode, the optocoupler is turned on to increase the duty cycle and thus increase the output voltage; conversely, when the output voltage is higher than the Zener diode, the optocoupler is turned off to decrease the duty cycle and thus decrease the output voltage.
If the secondary load of the high-frequency transformer is overloaded or the switching circuit is faulty, there will be no power supply from the optocoupler. The optocoupler will then control the switching circuit to prevent it from oscillating, thus protecting the switching transistor from being damaged and burned out.
Here are some recommended products from different series of Meco Optocouplers, distributed by Gongcai.com; product models include: MPC30XX-4L series, MPC101X series, MPC354, MPC356, MPH-314, MPH-341, MPC816, MPC817, as well as MPCM501, 6N137, etc.
The MPH-341 and MPH-314 series optocouplers are ideal for driving power inverters and inverters and MOSFETs for motor control; they contain an LED optically coupled to an integrated circuit with a power output stage; the optocouplers maintain their operating parameters within a temperature range of -40°C to +110°C.
MPH-314 operating range: 10 to 30 volts (VCC) with a maximum peak output current of 1.0A; low voltage lockout protection with hysteresis; and a maximum propagation delay of 110 ns.
The MPH-341 operates within a 15 to 30 volt (Vcc) range with a 3.0A peak output current, capable of directly driving most IGBTs with higher ratings up to 1200 V/200 A. For higher-rated IGBTs, the MPH-341 series can be used to drive discrete power stages that drive IGBT gates. An optocoupler, also known as an optocoupler, is a device that converts optical signals into electrical signals. In switching power supplies, optocouplers play a crucial role, improving not only the stability and reliability of the power supply but also enhancing its safety.
Switching power supplies are an indispensable part of modern electronic devices. They convert input alternating current (AC) into stable direct current (DC), providing the power required by various electronic devices. In switching power supplies, optocouplers are mainly used to achieve power isolation and feedback control.
First, optocouplers enable power supply isolation. In switching power supplies, a certain degree of isolation is required between the input and output terminals to prevent electrical shocks and faults from affecting the equipment. Optocouplers transmit information via optical signals, completely isolating the input and output terminals, thereby ensuring the safety and stability of the power supply.
Secondly, optocouplers also play a role in feedback control in switching power supplies. Switching power supplies require feedback control to stabilize the output voltage, and optocouplers are the key component for achieving this function. Optocouplers can convert changes in output voltage into optical signals, and then transmit these signals back to the control terminal, thereby achieving precise control of the output voltage. This feedback control method can effectively reduce output voltage fluctuations and improve the stability and reliability of the power supply.
Besides the two functions mentioned above, optocouplers offer several other advantages in switching power supplies. For example, they have a fast response speed, allowing for rapid adjustment of the output voltage in response to changes. Furthermore, optocouplers are small in size and weight, facilitating installation and use.
