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Hello everyone, in this lesson we will learn the characteristics of diodes

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There are actually many characteristics of diodes

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Moreover, when the diode works in different states, its characteristics are also different.

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Here we only talk about the characteristics of the diode when it works in the forward direction

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When the diode works in the forward direction,

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the most important characteristic is the one-way conductivity

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This means that the diode only allows current to flow from the positive pole to the negative pole,

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and does not allow current to flow from the negative pole to the positive pole

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There is another characteristic of the diode when it works in the forward direction,

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that is, there is a forward voltage drop

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Forward voltage drop is also called threshold voltage

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The threshold voltage of the silicon tube is 0.7 volts,

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and the threshold voltage of the germanium tube is 0.3 volts

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When understanding the forward voltage drop of a diode,

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a diode can be compared to a highway toll booth

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When passing through this toll booth, we need to pay 100 yuan

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If we brought 500 yuan, we only have 400 yuan left after passing through this toll booth

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If we have 50 yuan with us, we cannot pass through this toll booth

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Speaking of diodes, if this is a silicon tube

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The voltage drop across the silicon tube is 0.7 volts

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Input a voltage of 3 volts, and only 2.3 volts are left after passing through the diode

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According to these two characteristics of the diode, we can get the conduction condition of the diode

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That is, the positive pole is greater than the negative pole,

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and the voltage difference between the positive and negative poles is greater than the forward voltage drop

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The third characteristic is used after the diode is turned on

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That is, after the diode is turned on, the positive pole is greater than the negative pole

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We need to combine the following two circuit diagrams to understand the voltage drop of the diode

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We must first know that the voltage at the ground point and the power supply point will never change

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The point of grounding is always 0 volts,

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and the point connected to the power supply is always the voltage of the power supply

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Assuming both diodes are silicon diodes, they both have a voltage drop of 0.7 volts

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When the circuit diagram on the left is not working, the positive pole of the diode is 5 volts,

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and the negative pole is 0 volts.

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The positive pole is greater than the negative pole,

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and the voltage difference between the positive and negative poles

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is greater than the forward voltage drop of the diode

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Then the diode can conduct

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After conduction, the positive pole will only be 0.7 volts greater than the negative pole

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Observe the circuit diagram and connect the power supply to the anode of the diode

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Then the positive pole is always the power supply voltage, 5 volts

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In order to meet the third characteristic of the diode,

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the cathode voltage of the diode will become 4.3 volts

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Let's look at the circuit diagram on the right

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When the circuit is not working, the positive pole is 5 volts and the negative pole is 0 volts.

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The positive pole is greater than the negative pole,

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and the positive and negative voltage difference is greater than the voltage drop of the diode

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Then the diode can conduct

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We continue to observe this circuit

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It can be seen that the negative pole of the diode is directly grounded,

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so the negative pole voltage is always 0 volts

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In order to meet the third characteristic of the diode, only the anode voltage of the diode can change

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Positive voltage becomes 0.7 volts