Terminology Explanation of Diode Parameters

Terminology Explanation of Diode Parameters

The polar capacitance of a diode

We know that diodes have the characteristic of easily passing current from P-type to N-type semiconductors, but not easily passing in the opposite direction. The combination of these two characteristics creates the function of a capacitor, which is to accumulate charge. Accumulation of electric charge requires discharge. Discharge can occur in any direction. Strictly speaking, the statement that diodes only have current flowing in one direction is not valid. This situation is evident at high frequencies. Therefore, it is better to have a small capacitance at the anode of the diode.

Maximum rated value

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The maximum reverse peak voltage VRM, even without reverse current, will eventually damage the diode as long as the reverse voltage is continuously increased. This type of reverse voltage that can be applied is not an instantaneous voltage, but a repeatedly applied forward and reverse voltage. The maximum value of the AC voltage applied to the rectifier is a critical factor specified.

The maximum reverse voltage VR mentioned above is the peak voltage repeatedly applied, and VR is the value obtained when a continuous DC voltage is applied. For DC circuits, the maximum DC reverse voltage is important for determining the allowable and upper limits.

Maximum surge current Isurge

Excessive forward current allowed to flow. It is not a normal current, but an instantaneous current, and this value is quite large.

Maximum average rectified current IO

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The maximum value of the average rectified current flowing through the load resistor in a half wave rectification circuit. This is a very important value during design.

Maximum AC input voltage VI

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The effective value of a sinusoidal AC voltage applied to a half wave rectifier circuit (resistive load). This is also a very important parameter when choosing a rectifier. The maximum peak forward current IFM is the maximum current value that flows forward, which is also an important parameter in designing rectifier circuits.　　Maximum power P

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When current flows through a diode, it absorbs heat, causing its own temperature to rise. The maximum power P is the maximum value of power. Specifically, it is the product of the voltage applied across the diode and the current flowing through it. This limit parameter is particularly important for voltage regulators and variable resistance diodes.

Reverse current IR

Generally speaking, there is no reverse current flowing through a diode. In fact, when a certain reverse voltage is applied, there will always be a current flowing through, which is the reverse current. It goes without saying that good diodes have smaller reverse currents.

Reverse recovery time

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When changing from forward voltage to reverse voltage, the ideal situation is that the current can be instantly cut off, but in reality, it usually requires a slight delay. The amount that determines the current cutoff delay is the reverse recovery time. Although it directly affects the switching speed of the diode, it does not necessarily mean that a small value is enough.