In modern semiconductor industry power electronic control systems, MOSFETs (Field-Effect Transistors) are widely used in motor control systems of motor drives, power tools, and home appliances due to their high efficiency and fast switching characteristics. Because motor drives typically require efficient power control and regulation, motors place a series of stringent requirements on MOSFETs, including voltage withstand capability, on-resistance, switching speed, and thermal management. This article will discuss in detail the key requirements of motors for MOSFETs. 1. High Voltage Withstand Capability Voltage fluctuations in motor drive systems are significant, especially during motor start-up, stopping, or load changes, which may generate high voltage spikes (such as back electromotive force). Therefore, MOSFETs need to have high voltage withstand capability to withstand these transient voltages without breakdown or failure. Especially in high-power motor applications, the voltage withstand capability of the MOSFET usually needs to be a safety margin higher than the motor's operating voltage, typically 1.2 to 1.5 times the motor voltage. Solution: Select a MOSFET suitable for the motor's operating voltage. Common rated voltage ranges are 30V to 1500V. For high-voltage motor applications, selecting high-voltage MOSFETs (such as 900V or 1200V) can effectively prevent damage caused by overvoltage. 2. Low On-Resistance (Rds(on)) The on-resistance of a MOSFET directly affects its power loss and efficiency in the on-state. In motor drive systems, MOSFETs need to withstand large currents; therefore, low on-resistance is crucial for reducing switching losses and improving system efficiency. Lower on-resistance reduces power loss, heat generation, and improves system energy efficiency. Solution: When selecting MOSFETs, products with low on-resistance (Rds(on)) should be prioritized, especially for high-current motor drive systems. Modern power MOSFETs utilize advanced process technology to effectively reduce on-resistance and improve efficiency. 3. High Switching Frequency In motor drives, the switching speed of the MOSFET has a significant impact on system performance and efficiency. Especially in high-frequency PWM (Pulse Width Modulation) control modes, MOSFETs need a high switching frequency to maintain system stability while precisely controlling motor speed and torque. Higher switching frequencies enable motor drive systems to provide sufficient power output in a smaller size and weight. Solution: Select MOSFETs with faster switching speeds, such as those with low gate charge (Qg) and good switching characteristics. Furthermore, proper drive circuit design is also crucial for increasing the switching frequency, ensuring the MOSFET can respond quickly at the operating frequency. 4. Low Switching Losses Motor drive systems frequently switch the switching state (on and off) of MOSFETs during operation, incurring switching losses. Especially under high-frequency PWM control, switching losses increase significantly, affecting overall efficiency and generating excessive heat. Therefore, low switching losses are particularly important for MOSFET selection. Solution: Select MOSFETs with low switching loss characteristics, such as those using soft-switching or zero-voltage switching (ZVS) technology. These MOSFETs typically have lower switching times and transition losses, helping to reduce system power loss and heat accumulation. 5. Thermal Management Capability Power MOSFETs in motor drive systems typically need to withstand large currents and power losses, leading to increased device temperature. Insufficient heat dissipation can cause MOSFETs to fail due to overheating. Therefore, good thermal management design is crucial. The thermal resistance and package design of MOSFETs directly affect their heat dissipation efficiency. Solution: Select MOSFETs with good thermal performance, especially in high-power applications. Package types (such as TO-220, TO-247, etc.) need to have sufficient heat dissipation capacity. Furthermore, the system design needs to consider appropriate heat dissipation solutions, such as heat sinks, fans, or liquid cooling systems, to ensure that the MOSFET's temperature is maintained within a safe range during operation. 6. Electromagnetic Interference (EMI) Immunity Electromagnetic interference (EMI) is a common problem in motor drive systems, especially during high-frequency switching operations, which can generate significant electromagnetic noise. MOSFETs may generate high-frequency noise during switching. If this noise cannot be effectively suppressed, it may affect the stability of the entire system and even cause malfunctions in other sensitive circuits. Solution: Select MOSFETs with good EMI immunity and combine them with appropriate EMI suppression measures, such as filters and shielding, to reduce the impact of noise on the system. In addition, reasonable PCB layout and grounding design are also important means of reducing EMI. 7. High Temperature Resistance Motor drive systems may operate in high-temperature environments, especially in applications such as power tools or electric vehicles, where system temperatures can rise significantly. MOSFETs require high high-temperature resistance to prevent performance degradation or failure due to overheating. Solution: Select MOSFETs with a wide operating temperature range. Typically, MOSFETs in motor drive systems need to operate from -40°C to +150°C. Furthermore, using high-temperature stable materials and packaging designs can enhance the high-temperature resistance of MOSFETs. Motor requirements for MOSFETs encompass multiple aspects, including voltage withstand capability, on-resistance, switching speed, switching losses, thermal management capabilities, electromagnetic interference immunity, and high-temperature resistance. For different application scenarios, designers need to select appropriate MOSFET types and combine them with good circuit design and heat dissipation solutions to ensure the efficient and stable operation of the motor drive system. By optimizing the selection and use of MOSFETs, the performance of the motor drive system can be improved, its lifespan extended, and the overall system efficiency enhanced.
