Why diodes can only be turned on forward

This can only be explained by the p-n junction material inside the diode (which also has this structure in triodes).

When the p-n junction is not applied with an applied voltage, the diffusion motion and the drift motion are in dynamic equilibrium, and the current through the p-n junction is zero.

When the positive pole of the power supply is connected to the P region and the negative terminal is connected to the N region, it is called adding forward voltage or forward bias to the PN junction, because the PN junction is a high-resistance region, and the resistance of the P and N regions is very small, so the forward voltage is almost all added to both ends of the PN junction. An external electric field is generated on the p-n junction in the opposite direction to the inner electric field, and under its propulsion, the electrons in the n-region are to diffuse to the left and neutralize with the positive ions in the original space charge region, narrowing the space charge region. Similarly, the holes in the p-region should spread to the right and neutralize with the negative ions in the original space charge region, narrowing the space charge region.

As a result, the internal electric field is weakened, and the original dynamic equilibrium of the pN junction is destroyed. So the diffusion motion overtakes the drift motion, and the diffusion continues. At the same time, the power supply continuously replenishes the positive charge to the p-region and the negative charge to the n-region, resulting in a large forward current IF in the circuit.

Moreover, if increases as the forward voltage increases.

When the positive terminal of the power supply is connected to the n-region and the negative pole is connected to the p-region, it is called adding a reverse voltage or reverse bias to the PN junction. The direction of the applied electric field generated by the reverse voltage is the same as that of the internal electric field, which strengthens the electric field in the pn junction, and pulls away the many sons (holes) in the p region and the many sons (free electrons) in the n region from the vicinity of the pn junction, which further widens the pn junction, increases the resistance of the pn junction, breaks the original equilibrium of the pn junction, and the drift motion under the action of the electric field is greater than the diffusion motion. At this time, the current through the p-n junction, mainly the drift current formed by the few tons, is called the reverse current ir.

Because at room temperature, the number of minority carriers is not much, so the reverse current is very small, and when the applied voltage changes within a certain range, it hardly changes with the change of the applied voltage, so the reverse current is also called the reverse saturation current. When the reverse current is negligible, the PN junction is considered to be in a cut-off state.

It's a very speechless question. The diode itself was invented based on the unidirectional conductive characteristic.

The condition under which the diode is turned on is greater than the dead zone voltage.

1. Correct connection direction: When connecting the diode, the positive pole must be connected to the positive pole of the power supply, and the negative pole must be connected to the negative pole of the power supply.

2. The voltage must be greater than the forward bias voltage: under the action of the external power supply, the positive voltage of the diode must be greater than the forward bias voltage of the diode in order to be turned on.

3. The concentration of forward doping should be high: the concentration of forward doping has a great impact on the on-voltage of the diode, and the higher the concentration, the lower the on-voltage.

4. Ensure that the temperature is moderate: when the temperature of the diode is too high or too low, it will cause the electrical performance parameters of the diode to change, resulting in the diode cannot be turned on.

When the above conditions are satisfied, the diode will be turned on forward, and the current will flow from the positive electrode to the negative electrode in the form of carrying current, so that the circuit can be closed.

A diode is one of the simplest electronic components, which has the characteristics of forward conduction and reverse cut-off, and its main functions are as follows:

1. Rectification: The diode can convert alternating current into direct current, that is, by using the different forward conduction and reverse cut-off characteristics of the diode, and adding the appropriate number of components to the circuit, the rectification of alternating current can be realized.

2. Protection: The diode can be used as a protection element in the circuit to protect the load circuit from bad signals such as overvoltage and overcurrent. For example, in DC circuits, by connecting a diode in series, the diode automatically cuts off the excess voltage when the voltage is too high, which can also prevent the negative effects of management errors.

3. Voltage stabilization: The reverse cut-off characteristics of the diode can be used to produce a regulated power supply. This kind of circuit is characterized by stable voltage, small fluctuation, good stability and anti-interference ability.

4. Detection: The diode can be used to detect in high-frequency circuits and convert the modulated signal into the original signal. This method is widely used in radios, televisions and other equipment.

5. Light emitting: In some diodes, when the PN junction emits light, it is also called a light-emitting diode (LED). It can be used for indications or signal prompts, and can also be used as a backlight for displays.

To sum up, diodes are widely used in various fields such as electronic circuits, communications, automatic control, and computers.

Firstly, the potential difference between the two ends of the diode is analyzed, so as to determine whether the forward voltage or the reverse voltage is added to the two ends of the diode. If the voltage is reversed, the diode is in the cut-off state.

If the forward voltage is less than the dead zone voltage of the diode, the diode is still in the cut-off state; The diode can only be turned on if the forward voltage is greater than the dead zone voltage.

In the process of judging by the above method, if there are more than two diodes subjected to forward voltages of different sizes, it should be determined that the one with the larger forward voltage should be preferentially turned on, and the voltage at both ends is the forward conduction voltage, and then the working state of other diodes should be judged by the above method.

That is to say, the voltage at both ends of it must reach so much to be regulated, and 12V1W needs 12V, which is its breakdown voltage. If it doesn't reach that big, it's still in reverse cutoff. The Zener diode is made to turn it on in reverse.

Regulator diodes;

Zener diode, English name zener diode, also known as Zener diode. This is a voltage regulator diode that uses the phenomenon that the current can change over a wide range while the voltage remains basically unchanged in the reverse breakdown state of the PN junction. This diode rock residual tube is a semiconductor device with very high resistance until the critical reverse breakdown voltage.

At this critical breakdown point, the reverse resistance is reduced to a very small value, in which the current rolls up roughly while the voltage remains constant, and the Zener diode is binned according to the breakdown voltage, because of this characteristic, the Zener is mainly used as a voltage regulator or voltage reference element. Zener diodes can be connected in series for use at higher voltages, and higher stabilizing voltages can be obtained by connecting them in series.

There are two questions that you need to figure out in order to answer this question.

The first problem you should know is that the forward on-resistance of the diode, which is nonlinear, the greater the current passing through, the smaller the resistance, that is, it is inversely proportional to the current.

The second question is how a multimeter measures resistance. You can think of the inside of a multimeter as a circuit with a battery and a resistor in series, (a 10k leg battery is 9v).

When measuring, the resistance to be measured is connected in series with the internal battery resistance, and then the current flowing through controls the deflection of the pointer to read out the resistance. The range selection of the multimeter resistance is determined according to the size of the internal resistance, the internal resistance of the 1st gear is the smallest, the 10th gear is larger, and so on.

Because the internal resistance of the 1st gear is different from the 100th gear, the diode is a p-n junction.

The voltage applied to the diode by the 1st and 100th multimeters is different.

Through experiments, we can understand what is diode forward conduction.

I use it wrong, I remember that I used *10, and 100 is a bit big, and I can't remember the specific reason.

Through experiments, we can understand what is diode forward conduction.

A forward voltage is given, and it is greater than the on-voltage of the diode!

It is the forward conduction voltage of the silicon tube (the germanium tube is about, and the voltage at both ends of the diode remains basically unchanged after the conduction.

1. The diode is added with external forward voltage (the external reverse voltage cannot be turned on);

2. The forward voltage added must be greater than the dead zone voltage of the diode.

The dead-zone voltage of the diode

When the forward voltage is applied, at the beginning of the forward characteristic, the forward voltage is small 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. This forward voltage, which does not 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 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. It is called the threshold voltage or threshold voltage, and the silicon tube is about, and the germanium tube is about.

The forward conduction voltage drop of a silicon diode is about, and the forward conduction voltage drop of a germanium diode is about.

How diodes workThe crystal diode is a p-n junction formed by a p-type semiconductor and an n-type semiconductor, which forms a space charge layer on both sides of its interface and has a self-built electric field. In the absence of an applied voltage, the diffusion current caused by the difference in carrier concentration on both sides of the PN junction and the drift current caused by the self-generated electric field are equal. When there is a forward voltage bias in the external area, the mutual suppression effect of the external electric field and the self-built electric field increases the diffusion current of the carriers and causes the forward current.

When there is a reverse voltage bias in the outside world, the external electric field and the self-built electric field are further strengthened to form a reverse saturation current i0 that is independent of the reverse bias voltage value within a certain reverse voltage range. When the applied reverse voltage is high to a certain extent, the electric field strength in the charge layer of the pn junction space reaches a critical value, resulting in the multiplication process of carriers, generating a large number of electron-hole pairs, and producing a large reverse breakdown current, which is called the breakdown phenomenon of the diode. The reverse breakdown of the PN junction is divided into Zener breakdown and avalanche breakdown.

Hard City Diode.

There are left and right voltages at both positive and negative ends, and the on-current required for forward passage can also be understood.

When the diode is applied to the forward voltage, as long as the applied voltage is greater than the pn junction on-voltage (silicon tube, the diode is on.

When the forward voltage is greater than the dead zone voltage, the electric field in the PN junction is overcome and the diode is turned on.