Diode data parameters and distinction between positive and negative poles
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Diode data parameters and distinction between positive and negative poles

Posted Date: 2024-02-08

Diodes are mainly composed of two different semiconductor materials, they are called P-type semiconductor and N-type semiconductor. These two materials are combined in a specific way to form the structure of the diode.

P-type semiconductor material: P-type material is formed by doping trivalent elements (such as boron, aluminum, etc.) into pure silicon or other semiconductor materials. These trivalent elements introduce small numbers of holes (positive charge carriers) into the semiconductor material.

N-type semiconductor material: N-type material is formed by doping pentavalent elements (such as phosphorus, arsenic, etc.) into pure silicon or other semiconductor materials. These pentavalent elements introduce excess electrons (negative charge carriers) into the semiconductor material.

When P-type and N-type semiconductor materials come together and combine, an interface called a PN junction is formed. In the P region of the PN junction, holes are the dominant carriers; in the N region, electrons are the dominant carriers. When the diode is in a forward biased state, that is, positive voltage is applied to the P region and negative voltage is applied to the N region, current can flow through the PN junction, forming a forward current. When the diode is in a reverse biased state, that is, a negative voltage is applied to the P region and a positive voltage is applied to the N region, the current can hardly flow through the PN junction, forming a small reverse current.

Therefore, the material composition of the diode is to form a PN junction between the P-type semiconductor and the N-type semiconductor, and the characteristics of the PN junction are used to achieve one-way conduction of current.

Diode data parameters

When using diodes, be careful not to exceed the maximum ratings for voltage, current, temperature, etc.

Diode Maximum Rating

The maximum rating indicates the limit guaranteed by the manufacturer to the user. Use beyond the limit may cause damage. Damage may result. The following parameters are usually specified:

(1) Reverse peak voltage VRRM. It usually indicates the maximum allowable AC voltage when an AC voltage with a frequency of 50Hz is applied to the diode.

(2) Reverse DC voltage VR. Indicates the maximum reverse DC voltage that can be continuously loaded on the diode.

(3) Forward peak current IFM. It usually indicates the maximum allowable AC current when an AC current with a frequency of 50Hz is applied to the diode.

(4) Continuous forward current I0. Indicates the maximum value of DC current that can flow continuously in the forward direction applied to the diode. (A high temperature will cause the diode to be damaged, so it is necessary to specify the maximum forward current)

(5) Inrush current IFSM. Indicates the maximum value of the instantaneous current that allows the diode to conduct in the forward direction at one time. The power-on time is specified as a condition and is generally set to 1s.

(6) Allowable loss P. Limit value of electric power loss due to heat generated for zener diodes, etc.

(7) Maximum Zener current Iz. The maximum value of the Zener current that the Zener diode can conduct in the reverse direction is determined by the allowable loss (power) and the Zener voltage.

How to distinguish the positive and negative poles of a diode

A diode is a semiconductor device with two electrodes, one of which is called the positive electrode (anode/collector) and the other is called the negative electrode (cathode/emitter). Here are several ways to distinguish the positive and negative poles of diodes:

1. Observe the device identification: Most diodes will be marked with identification, such as model number, letters or symbols. On the logo, there are usually symbols representing positive and negative poles, such as arrows, plus signs, lines, triangles, etc. The positive symbol is common and usually indicates the direction of current flow.

2. Look at the package shape: The package shape of the diode can also provide some clues. Generally speaking, the positive electrode is usually connected to a larger metal contact surface, while the negative electrode is usually connected to a smaller metal contact surface. For example, general-purpose diodes (such as glass-encapsulated diodes) usually have a longer metal pin that connects to the anode (positive pole) and a shorter pin that connects to the cathode (negative pole).

3. Use a multimeter to measure conductivity: Set the multimeter to the diode test position (diode test or diode forward voltage amplification) and perform a conductivity test. Under normal circumstances, when a forward voltage passes through, the current will flow from the anode to the cathode, showing a small positive current value. If reverse voltage passes, the current value should be infinite (open circuit).

Review Editor: Huang Fei


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