The principle of diodes and the guidance of positive and negative diodes

The diode is forward-conducted, and the reverse is switched off.

Diodes are semiconductors that have unidirectional conductivity and can only go from the positive to the negative pole of the power supply.

Diode Symbol:

The head of the diode triangle (with a vertical bar) is the negative pole.

3.The horizontal line crosses the triangle, and the vertex of a bright pin is the negative pole, and the side that is empty and coincidental is the positive pole.

Ideal diodes, where the forward current is exponentially related to the voltage. However, when the actual diode is applied with a forward voltage, the forward voltage is small at the beginning of the forward characteristic, which is not enough to overcome the blocking effect of the electric field in the PN junction, and the forward current is almost zero, which is called the dead zone. The forward voltage that cannot turn the diode on is called the dead zone voltage.

When the forward voltage is greater than the dead zone voltage, the electric field in the PN junction is overcome, the diode is turned on positively, and the current rises rapidly with the increase of voltage. The increase is very fast, so the voltage drop on the diode is actually very small, otherwise it will burn out due to too much current. The terminal voltage of the diode remains almost constant when turned on over the current range of normal use, and this voltage is called the forward voltage of the diode.

When the forward voltage at both ends of the diode exceeds a certain value, the internal electric field is quickly weakened, the characteristic current increases rapidly, and the diode is forward-conducted.

In an ideal diode, when the applied reverse voltage does not exceed a certain range, the current through the diode is the reverse current formed by the drifting movement of a few carriers. Since the reverse current is small, the diode is in a cut-off state. This reverse current is also known as the reverse saturation current or leakage current.

The reverse saturation current of a diode is highly affected by temperature. Generally, the reverse current of silicon tube is much smaller than that of germanium tube, and the reverse saturation current of low-power silicon tube is in the order of Na, and the reverse saturation current of low-power germanium tube is in the order of A. As the temperature increases, the semiconductor is heatedly excited, and the number of minority carriers increases, and the reverse saturation current also increases.

When the voltage does not reach the reverse breakdown voltage, the current of the diode is always equal to the directional saturation current. However, when the voltage is high enough to a certain extent, the diode is broken down in the opposite direction, and the current increases dramatically.

There are two types of reverse breakdown: Zener breakdown and avalanche breakdown. Some diodes can be restored to their original state after removing the reverse voltage after breakdown, such as the regulator diode working in the reverse breakdown zone. Some reverse breakdown will burn out directly.

Solution: The voltage at both ends of the diode and the resistor = the sum of the two supply voltages = 5V (the current is positive clockwise), if it is assumed that there is no voltage drop on the resistor, then the diode has a positive voltage drop, so it is on. Then the VO voltage is equal to the sum of the voltage drop of the diode (ideally 0) plus the 5V electric coarse source voltage, considering the direction of the service, so VO=-5;Finally concluded:

The diode is a positive conductor and answers the old one, vo=-5v

The characteristic of diodes is that they are conductive in one direction. In a circuit, current can only flow in from the positive pole of the diode and out from the negative pole. Forward characteristics of the diode:

In electronic circuits, the positive pole of the diode is connected to the high potential end and the negative terminal is connected to the low potential end, and the diode will be turned on, and this connection method is called forward bias.

Two methods:1Looking at the two contacts of the diode, the long one is the negative pole, and the other end is the positive pole;

2.Looking at the logo, one end with the sign is the negative pole and the other end is the positive pole.

1. For ordinary diodes, you can look at the surface of the tube body, and one end with a white wire is the negative electrode.

2. For light-emitting diodes, the long pin is positive, and the short one is negative.

3. If the pins are cut to the same length, the small metal inside the LED body is the positive electrode, and the large sheet is the negative electrode.

4. If the eyes are short-sighted and cannot see clearly, you can also turn on the multimeter, turn the knob to the on/off gear, and connect the red and black watch pens to the two pins respectively. If there is a reading, one end of the red pen is positive; If the reading is "1", one end of the black pen is positive.

1. The long leg of the light-emitting diode is positive, and the short leg is negative. If the feet are the same length, the big point inside the LED is the negative electrode, and the small one is the positive electrode. Some light-emitting diodes have a facet with a lead near the facet as a negative pole.

2. In the multimeter: red pen connection "+ black pen connection" - "When measuring the light-emitting diode, the low resistance cannot be measured, and the RX10K file can be used to measure, and the two meter pens are in contact with the two stages of the diode. If the resistance is small, the black pen is connected to the positive pole, and if the resistance is large, the black pen is connected to the negative pole.

When the light-emitting diode is connected to a TTL component, a 470R step-down resistor is generally connected in series to prevent damage to the device.

3. The crystal diode is composed of a PN junction, two electrode leads and a tube shell. Crystal diodes are encapsulated with wires on both sides of the PN junction. The letter symbol of the crystal diode is that the direction of conduction of the junction is from p-type semiconductor to n-type semiconductor, that is, P to N conduction (P is the positive electrode, N is the negative electrode).

The PN junction is forward-conductive and reverse-cut-off, and has the characteristics of single-phase conductivity.