How to ensure the steady-state and dynamic current balance of super junction power mosfet in parallel applications?
Publish Time: 2025-03-27
Super junction power mosfet has been widely used in power electronic systems for its low on-resistance, high breakdown voltage and excellent switching performance. Especially in situations where large current handling is required, the use of MOSFETs in parallel has become a common solution to disperse current, reduce power consumption and limit the maximum junction temperature. However, the problem of steady-state and dynamic current balance in parallel applications has become the key to ensuring system performance and reliability.In terms of steady-state current balance of parallel MOSFETs, it mainly depends on the matching of device parameters. The on-resistance RDS(on) of super junction power mosfet is a key factor affecting current distribution. Choosing MOSFETs with similar RDS(on) can significantly reduce the problem of current unevenness. In addition, the consistency of transconductance GFS is also crucial, which affects the current control capability of MOSFET. Choosing devices with consistent GFS helps to achieve more uniform current distribution. When designing the PCB, the layout of the parallel MOSFET should be made symmetrical as much as possible, and the source, drain and gate trace lengths of each device should be consistent to reduce the current unevenness caused by trace impedance differences.Dynamic current balancing is more complex because it involves the switching process of the MOSFET. In parallel applications, due to differences in the threshold voltage Vth and switching time of the devices, some MOSFETs may turn on early or turn off late, resulting in uneven current. To solve this problem, a series of measures need to be taken. First, select MOSFETs with similar Vth values and switching times to reduce changes during transients. Second, a small resistor is connected in series with the gate of each MOSFET, which not only suppresses gate oscillations but also helps balance the gate drive current, thereby achieving a more uniform switching process. In addition, ensuring that the gate drive circuit can drive the parasitic capacitance of multiple MOSFETs without overheating is also key to achieving dynamic current balancing.In practical applications, the effect of heat dissipation conditions on current balancing also needs to be considered. Super junction power MOSFETs generate a lot of heat when working. If the heat dissipation conditions are inconsistent, it will cause RDS(on) changes, which in turn affects current distribution. Therefore, it should be ensured that the heat dissipation conditions of each MOSFET are the same, and they can be installed on a common heat sink or copper plane to maintain the same temperature.To further improve the current balancing performance of parallel MOSFETs, advanced control strategies can also be used. For example, a current sensor is used to detect the current of each MOSFET, and the gate voltage is adjusted through feedback control to achieve dynamic current sharing. Although this method will increase the complexity of the circuit, it can significantly improve the performance and stability of the system.In short, to ensure the steady-state and dynamic current balance of super junction power mosfet in parallel applications, it is necessary to comprehensively consider multiple aspects such as device selection, PCB design, gate drive circuit, heat dissipation conditions, and control strategy. Through scientific design and rigorous testing, the performance of parallel MOSFETs can be fully utilized to meet the needs of high current applications.
