The internal structure of MOSFETs and IGBTs differs significantly, which leads to distinct application areas. MOSFETs are typically capable of handling large currents—up to kiloamperes—but their voltage blocking capability is generally not as strong as that of IGBTs. On the other hand, IGBTs can manage high power levels with both high current and voltage, making them suitable for applications where high power is required. While IGBTs can achieve switching frequencies up to 100 kHz in hard-switching scenarios, they are still outperformed by MOSFETs, which can operate at hundreds of kHz, even up to MHz or higher, especially in RF applications.
In terms of application, MOSFETs are commonly used in high-frequency power supplies such as switching power supplies, ballasts, induction heating, inverters, and communication power systems. IGBTs, on the other hand, are more often found in welding machines, inverters, electroplating systems, and high-power induction heating equipment. The performance of a Switch Mode Power Supply (SMPS) largely depends on the selection of power semiconductor devices, including both switching transistors and rectifiers.
Although there is no one-size-fits-all solution when choosing between IGBTs and MOSFETs, a detailed comparison of their performance in specific SMPS applications can help determine the optimal choice. This article explores several key parameters, including switching losses in both hard-switching and soft-switching ZVS (Zero-Voltage Switching) topologies, along with the three main types of power switching losses: conduction loss, turn-on loss, and turn-off loss. It also discusses how the recovery characteristics of diodes influence the conduction switching losses of MOSFETs and IGBTs, especially in hard-switching topologies.
Conduction loss is an important factor in evaluating device performance. In addition to the longer voltage drop time of IGBTs, their turn-on characteristics are similar to those of MOSFETs. However, due to the minority carrier storage effect in the PNP BJT within the IGBT structure, there is a voltage tail during the turn-on phase. This results in a quasi-saturation effect, which delays the collector-emitter voltage from reaching its VCE(sat) value immediately. In ZVS conditions, this can cause the VCE voltage to rise when the load current switches from the anti-parallel diode to the IGBT’s collector.
The Eon energy consumption listed in IGBT data sheets represents the integral of the product of the collector current and VCE over each cycle, measured in joules. It includes various losses associated with saturation and is divided into two components: Eon1 and Eon2. Eon1 refers to the loss without considering the energy related to diode recovery, while Eon2 includes the conduction energy associated with diode recovery. Testing Eon2 typically involves using the same diode as the one in the IGBT package.
In hard-switching circuits, factors like gate drive voltage, impedance, and diode recovery characteristics determine the Eon switching loss. For example, in a conventional CCM boost PFC circuit, the recovery characteristics of the boost diode play a crucial role in controlling Eon energy. Selecting a diode with minimal Trr (reverse recovery time) and QRR (reverse recovery charge), along with soft recovery characteristics, helps reduce electrical noise and voltage spikes caused by the parasitic inductance in the circuit.
For hard-switching applications involving MOSFETs, the body diode recovery is a limiting factor, as it is generally slower than discrete diodes. Therefore, the operating frequency of the SMPS is often constrained by the body diode’s recovery time. In contrast, IGBTs are usually paired with optimized diodes that match their application requirements, allowing for better performance in high-frequency SMPS designs.
In addition to selecting the right diode, adjusting the gate drive source impedance can help control Eon loss. Reducing the impedance increases the conduction di/dt, which reduces Eon loss but may increase EMI. Finding the right balance between Eon loss and EMI requires careful testing and analysis of the device's conversion curve.
Turn-off loss is another critical parameter. Due to the tail current in IGBTs, their turn-off loss is generally higher than that of MOSFETs. This tail current is related to the removal of minority carriers in the PNP BJT structure. The Eoff energy dissipation in IGBTs is influenced by factors such as Miller capacitance, gate drive speed, and parasitic inductance in the circuit. Soft-switching topologies like ZVS and ZCS can significantly reduce these losses, though the benefits are more pronounced in MOSFETs due to their faster switching speeds.
In conclusion, the choice between MOSFETs and IGBTs depends on various factors, including circuit topology, operating frequency, ambient temperature, and physical size. MOSFETs excel in high-frequency applications due to their fast switching and low turn-off losses, while IGBTs are preferred in high-power, hard-switching environments where their robustness and efficiency are advantageous. Ultimately, the decision should be made based on a thorough evaluation of the application’s specific requirements.
Manual Lifting Column,Lifting Machine,Lift Mechanism,Linear Lifting Mechanism
Kunshan Zeitech Mechanical & Electrical Technology Co., Ltd , https://www.zeithe.com