The impact of reverse recovery time of diodes on device performance

1, Overview of reverse recovery time of diodes
The reverse recovery time of a diode refers to the time required for the diode to switch from a forward conducting state to a reverse blocking state. This time includes storage time (ts) and descent time (tf), i.e. tr=ts+tf. During the storage time, the reverse current remains high and the diode has not completely turned off; The descent time is the time when the reverse current gradually decreases to the specified value (usually 0.1 times the maximum reverse recovery current).
The reverse recovery time is actually caused by the charge storage effect. When the diode conducts in the forward direction, the charge at the PN junction interface accumulates, forming a stored charge. When the diode needs to switch to the reverse blocking state, these stored charges need to be depleted in order for the diode to completely turn off. Therefore, the reverse recovery time is the time required for the stored charge to be depleted.
2, The impact of reverse recovery time on device performance
Limit working frequency
The reverse recovery time of a diode has a significant impact on its operating frequency. In AC circuits, diodes need to complete the state switching from forward to reverse within each cycle. If the reverse recovery time accounts for a relatively large proportion of the entire cycle, then at high frequencies, the diode is not sufficient to effectively complete state switching, resulting in limited performance.
For example, in rectification applications, the ideal state is to make the reverse recovery time of the diode much shorter than its operating cycle. If the reverse recovery time is too long, it will cause the diode to fail to operate normally at high frequencies, thereby limiting the operating frequency of the entire device.
Increase switch losses
The longer the reverse recovery time of a diode, the longer it will allow current to flow in reverse for a period of time when it switches from a conducting state to a blocking state. This will cause the diode of the transistor or MOSFET connected in series to start conducting before it is completely turned off, resulting in switching losses. This type of loss is particularly significant in switch mode power supply applications.
Switching losses not only reduce the efficiency of equipment, but also increase its heat generation, which may lead to issues such as overheating protection. Therefore, in applications such as switching power supplies, special attention should be paid to the reverse recovery time of diodes, and diodes with shorter reverse recovery times should be selected to reduce switching losses.
Affects electromagnetic interference (EMI)
At the moment when the diode is turned off, the current in the circuit cannot immediately stop. Due to the presence of inductance, these currents will continue to flow and attempt to maintain their original path, thereby forming high voltage spikes in the circuit. These high voltage spikes can cause interference to other parts of the circuit, known as electromagnetic interference (EMI).
The longer the reverse recovery time of a diode, the more complex the current oscillation waveform generated, and the more severe the electromagnetic interference. Therefore, in high-speed switch circuits, special attention should be paid to the impact of the reverse recovery time of diodes on electromagnetic interference. By optimizing circuit layout, selecting appropriate diodes, and reducing switching frequency, electromagnetic interference can be effectively reduced.
Affects heat dissipation design
Due to the increased switching losses caused by reverse recovery time, the temperature rise of the diode itself increases. When designing, appropriate heat dissipation measures must be considered to ensure that the diode can operate normally within the allowable temperature range. If the heat dissipation design is improper, it may cause the diode to overheat and be damaged.
In addition, the reverse recovery time can also affect the thermal stability of the diode. Under high temperature conditions, the reverse recovery time of diodes may increase, further exacerbating switch losses and temperature rise issues. Therefore, when designing, it is necessary to consider the thermal stability of the diode and the comprehensive effect of heat dissipation measures.
3, Measures to optimize the reverse recovery time of diodes
Choose the appropriate diode
When selecting a diode, special attention should be paid to its reverse recovery time parameter. Choosing diodes with shorter reverse recovery time based on specific application requirements and working conditions can effectively reduce switching losses and electromagnetic interference.
Optimize circuit design
By optimizing circuit design, it is possible to reduce the current oscillation and voltage spikes of diodes during the switching process, thereby reducing electromagnetic interference and switching losses. For example, current waveforms can be smoothed and voltage spikes can be reduced by adding components such as inductors and capacitors.
Reduce the switching frequency
If allowed, reducing the switching frequency can effectively reduce the number of diode switches and switching losses. However, it should be noted that reducing the switching frequency may affect the overall performance and efficiency of the device. Therefore, a trade-off needs to be made between performance and efficiency.
Strengthen heat dissipation design
In order to ensure that the diode can operate normally within the allowable temperature range, it is necessary to strengthen the heat dissipation design. The heat dissipation efficiency can be improved by adding components such as heat sinks and fans, thereby reducing the temperature rise and switching losses of diodes.

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