Identification, classification and measurement of Diodes

Keywords: Identification, classification and measurement of Diodes

I,Symbol:"D, Vd, ZD"

Ordinary diode voltage regulator Diode

Light Emitting Diode photosensitive diode (photoelectric)

Fast Recovery Diode
Ii. Classification of level 2 pipes:

There are two types by material: one isSilicon Diode, And secondDiode. According to the manufacturing process, it is divided into a surface contact diode and a point junction diode. The following types are used: Rectification diode, detection diode, light emitting diode, voltage regulator diode, photosensitive (photoelectric) diode, switching diode, and fast recovery diode.

Difference between silicon and GE tubes: The on-voltage is different,The on-going voltage of the silicon tube is 0.7 V, and the on-going voltage of the GE tube is 0.3 V.(Forward bias voltage). Most of the materials used on the motherboard are silicon tubes.

III,Diode composition:

The diode is made of two semiconductor materials with different characteristics. One is a P-type semiconductor, and the other is a n-type semiconductor. The two semiconductors are connected by a special process, a pn junction is formed on the same interface. The positive pin is derived from the P material and the negative pin is derived from the N material.

Diode shape:

Two diode encapsulation methods are available.:

Plastic-enclosed diode glass Diode

Diode recognition:

Most of the diodes used on the motherboard are SMD diodes, which have red glass tubes and rectangular SMD shapes. These diodes generally have a special mark at one end, and the marked end is the negative electrode of the diode.

Iv. Features of Diodes:

Forward conduction, reverse cutoff(Unidirectional conduction)

Forward conduction:If the positive voltage of the diode is higher than the negative voltage (positive bias voltage), as long as the positive voltage reaches a certain value, the diode is turned on. After the diode is turned on, it is equivalent to a conductor, the resistance between the two pins of the diode is very small, which is equivalent to connection. The current flow direction is from the positive pole to the negative pole, the current cannot flow from the negative pole to the positive pole, otherwise the diode is damaged.

Reverse deadline:If the voltage added to the positive pole of the diode is lower than the negative voltage (reverse bias voltage), the diode is in the cutoff state, and the resistance between the two pins of the diode is very high, which is equivalent to an open circuit. As long as it is a reverse voltage, there is no current flow in the diode. If the reverse voltage is too large, the diode will break down and the current flows from the negative pole to the positive pole, which indicates that the diode is damaged.

Voltage Regulator diode has reverse breakdown characteristicsThe fast recovery diode is equivalent to two voltage regulator diodes.

V. Role of diodes:

Detection, rectification, voltage regulation, limit, switch, clamp, etc.

1. Rectification diode:

The function of a rectification diode is to convert an AC power supply into a pulsating direct current, which uses the unidirectional conductivity of the diode.

For the rectification circuit, due to the unidirectional conductivity of the diode, the diode VD is turned on when the AC voltage is normal for half a week. When the output voltage is negative for half a week, the diode VD ends and no output is made. After the pulse voltage rectified by diode VD is filtered by RC Filter, It is DC voltage.

2. Detection diode:

The detection diode is a device that detects low-frequency signals superimposed on high-frequency carriers. It has high detection efficiency and good frequency characteristics.

3. switching diode:

Based on the characteristics of one-way conduction of diodes, the current starting and stopping operations can be performed in the switching circuit.

4. Voltage Regulator diode:

A voltage regulator diode uses the reverse breakdown of a PN Junction to achieve voltage regulation. The voltage basically does not change with the current, the voltage regulator value of a voltage regulator diode is the voltage breakdown value (the voltage regulator value is selected based on the Load Voltage ).

, R1 provides throttling protection to protect the voltage regulator diode vd1. The purpose of this circuit's diode access is to stabilize the DC voltage of circuit. The working principle of this voltage regulator circuit is: the DC voltage + V is added to the vd1 through the resistance R1. Because the + V is greater than the vd1 Voltage Regulator value, the vd1 is in the breakdown state and the voltage is grounded, in this way, the voltage at both ends of vd1 remains unchanged, that is, the voltage at point A remains unchanged, so that the DC voltage supply circuit is stable.

5. Fast Recovery Diode (equivalent to two voltage regulator diodes ):

The function of voltage regulation protection in the circuit. This diode has good switching characteristics and short reverse recovery time. It is usually used as a rectification diode in a switching power supply.

6. LEDs:

Light Emitting Diode (LEDs) is a device that uses semiconductor materials, such as phosphating and phosphorus, to directly convert electric energy into light energy, it also features unidirectional conduction of common diodes.

7. photosensitive diode:

Converts light energy into electrical energy for optical control facilities.

Vi. measurement and determination of Diodes

1. diode Measurement

The multimeter is hit to the beeching diode, the red table pen is connected to the positive pole of the diode, and the black pen is connected to the negative pole of the diode. At this time, the positive resistance of the diode is measured, that is, the positive pressure drop value of the diode. The Forward Voltage Drop values of different diodes vary according to their internal materials.

2. Good or bad judgment

The positive pressure drop value reading at-is normal. If it is 0, it indicates that the diode is short-circuited or broken down. If it is 1, it indicates that the diode is open. Replace the table pen for another test. The reading value should be 1, that is, infinity. If not 1, the diode is damaged.

When the forward pressure drop is around 200, It is a voltage regulator diode. The two readings of the fast recovery diode are both normal at around 200.

Fast Recovery Diode Measurement Method

Vi. Principle of replacement of Diodes

1. the diode on the motherboard can be replaced as long as the size and appearance are the same, such as the red glass tube.

2. the diode between different purposes cannot be used as an alternative, and the diode cannot be used as an alternative.

3. Among the fast recovery diodes, rbyr1535, pbyr2045, and pbyr2545 can be used interchangeably, And the other models must be replaced by the original models.

4. When replacing the diode, you must recognize the positive and negative poles and cannot reverse the circuit. Otherwise, the circuit will not work properly.

5. When the diode is an open-circuit fault, you can directly use a new diode in parallel (soldered to the pin solder joints of the original diode ).

6. When you suspect that the diode is broken down or the performance is poor, remove the original diode and then weld the new diode.