Definition of power diode and waveform introduction of power diode dynamic process

A power diode is a semiconductor device capable of unidirectional conduction, allowing current to flow in one direction while exhibiting high resistance in another direction. Power diodes are commonly used in rectifier circuits to convert alternating current (AC) into direct current (DC). In the field of power electronics, power diodes are mainly used for high-power applications such as power conversion, industrial motor drive, wind power generation, and photovoltaic power generation systems.

The structure of a power diode is basically a PN junction composed of a P-type semiconductor and an N-type semiconductor. When a forward voltage is applied to the diode (i.e., the P-type terminal is positive and the N-type terminal is negative), the depletion region of the PN junction narrows and current can flow through the diode. At this point, the AD8275ARMZ-R7 diode conducts, and the magnitude of the current depends on the applied voltage and the characteristics of the diode. When a reverse voltage is applied (i.e., the N-type terminal is positive and the P-type terminal is negative), the depletion region widens, the diode exhibits a high resistance state, and the current is blocked.

The dynamic process of power diodes involves their working state in AC circuits, including two stages: conduction and cutoff. Throughout the entire communication cycle, the working state of the power diode will change with the variation of voltage, generating specific waveforms.

Conduction process:

When the AC input voltage becomes positive, the diode begins to conduct. During this process, the voltage of the diode rises from zero to the threshold voltage (turn-on voltage), at which point the depletion layer disappears and electrons can flow from the N region to the P region, causing the current to rapidly increase. The rate of current rise depends on the forward resistance of the diode and the external circuit. In an ideal state, the current rises in a right angled oblique shape, but in reality, due to the presence of capacitive and inductive effects, the rising edge will have a certain inclination.

Continuity maintenance:

After the diode is fully conductive, the waveform of the current will follow the positive half cycle of the AC voltage. In an ideal situation, the current waveform is the same as the input voltage waveform, but due to the forward voltage drop, the voltage waveform across the diode will actually be a constant voltage value lower than the input voltage.

Deadline process:

When the input voltage enters the negative half cycle, the diode begins to turn off. The current drops rapidly, but due to the presence of parasitic capacitance and inductance in the circuit, the actual current drop curve will have a certain lag and will not immediately drop to zero. The cutoff speed of a diode is affected by the reverse recovery time, which is the time required for the diode to recover from a conducting state to a cutoff state.

Deadline maintenance:

In the cut-off state, the diode is subjected to reverse voltage, which can be very high, requiring the diode to have sufficient reverse withstand voltage capability. In an ideal state, the current should be zero; However, in reality, there may be a weak reverse leakage current in the initial stage.

The dynamic characteristics of power diodes are crucial for their performance in power systems. For example, the design of devices such as inverters, rectifiers, and frequency converters must consider the characteristics of diode switching speed, forward and reverse voltage drop, and withstand voltage. When designing these devices, engineers need to choose appropriate power diodes based on the specific requirements of the application to ensure efficient and reliable operation of the system.