How to reduce the switching loss of the switch tube

The following are some effective ways to reduce the switching loss of the switch tube:

1. Choose the right switch tube. Switch tubes made of wide bandgap semiconductor materials such as silicon carbide (SiC) and gallium nitride (GaN) are good choices. Compared with traditional silicon-based switches, they have higher electron mobility, lower on-resistance and faster switching speed. For example, the on-resistance of silicon carbide MOSFET can be much lower than that of silicon-based MOSFET with the same withstand voltage level. This reduces the conduction loss. Due to its fast switching speed, it can reduce the voltage and current overlap time during the switching process, thereby reducing the switching loss. These wide bandgap semiconductor switches can also operate at higher temperatures and frequencies, which helps to improve the power density and efficiency of the switching power supply. For example, in high-frequency switching power supply applications, gallium nitride switches can work effectively at frequencies of hundreds of kHz or even several MHz, while traditional silicon-based switches have very large switching losses at such high frequencies.

2. Optimize the drive circuit of the switch tube and adjust the drive resistance. The drive resistance in the drive circuit has an important influence on the switching speed of the switch tube. By appropriately increasing the drive resistance, the turn-on and turn-off speed of the switch tube can be slowed down, and the voltage and current change rate (dv/dt and di/dt) during the switching process can be reduced, thereby reducing the switching loss. However, too large a drive resistance will also increase the turn-on and turn-off delay of the switch tube, affecting the working efficiency of the power supply. Therefore, it is necessary to optimize and adjust according to the characteristics of the switch tube and the specific circuit parameters. For example, in a switching power supply with MOSFET as the switch tube, the original drive resistance is 10Ω, and the switching loss is high. After adjusting the drive resistance to 20Ω through experiments, it is found that the turn-on and turn-off speed of the switch tube slows down, and the switching loss is reduced by about 30%, but at the same time, the turn-on and turn-off delays increase slightly, and the overall impact on the power supply performance needs to be considered comprehensively. Using active clamping drive technology, the active clamping drive circuit can effectively control the voltage spike of the switch tube during the turn-off process and reduce the switching loss. At the moment when the switch is turned off, the active clamping circuit can limit the voltage of the switch to a safe range, avoiding excessive voltage spikes that increase the loss of the switch. For example, in some flyback switching power supplies, after using active clamping drive technology, the turn-off voltage spike of the switch can be reduced from the original hundreds of volts to a reasonable range, greatly reducing the turn-off loss of the switch, while improving the reliability of the switch.

3. Application of soft switching technology Zero voltage switching (ZVS) and zero current switching (ZCS) Zero voltage switching technology refers to turning on the switch when the voltage is zero, and zero current switching technology refers to turning off the switch when the current is zero. Realizing ZVS or ZCS can significantly reduce switching losses. For example, in a resonant converter, by reasonably designing the parameters of the resonant circuit, the switch can be switched under zero voltage or zero current conditions. Taking the LLC resonant converter as an example, it uses the transformer leakage inductance and resonant capacitor to form a resonant network, which can achieve zero voltage switching of the switch. In this converter, when the switch is turned on, the voltage across the switch has dropped to zero. At this time, when the switch is turned on, there is almost no overlap of voltage and current, and the switching loss can be reduced to a very low level. Quasi-resonance technology Quasi-resonance technology is a soft switching technology improved on the basis of traditional hard switching circuits. It introduces resonance in the switching process of the switch so that the switch can be switched under conditions close to zero voltage or zero current. For example, in a quasi-resonance flyback converter, after the switch is turned off, the leakage inductance and parasitic capacitance of the transformer are used to form resonance, so that when the switch is turned on next time, the voltage across the switch has resonated to a lower value, thereby reducing the turn-on loss.

4. Optimize the circuit topology structure using a dual switch structure In some topologies, such as a dual-tube forward converter, two switches are used in series. This structure can distribute the voltage to the two switches when the switch is turned off, reduce the voltage stress on each switch, and thus reduce the turn-off loss. At the same time, the dual-tube structure can also improve the reliability of the converter because the probability of two switches failing at the same time is relatively low. Choose the right converter topology. Different converter topologies have different effects on the switching loss of the switch tube. For example, the phase-shifted full-bridge converter can achieve soft switching of the switch tube and reduce switching loss by controlling the phase shift between the bridge arms. Compared with the traditional hard-switched full-bridge converter, the phase-shifted full-bridge converter can reduce the switching loss by about 30% - 50% in medium and high power applications, effectively improving the efficiency of the power supply.