An ideal diode doesn't conduct any current at all if its cathode is more positive than its anode (or, by convention, the voltage across it is negative). On the other hand, an ideal diode conducts with no resistance at all if the anode is more positive than its cathode (or the voltage across the diode is positive). A diode whose anode is more positive than its cathode is also said to be 'forward-biased', while one whose cathode is more positive than its anode is 'reverse-biased'.
Of course, in the real world, there is no such thing as an ideal diode. A real diode would only start to conduct when the voltage across it exceeds a value referred to as its cut-in voltage (also known as 'break point', 'offset', 'threshold', or 'forward' voltage).
When the diode voltage is below the cut-in voltage, there is almost no current flowing through a diode. Once the diode voltage exceeds the cut-in voltage, the current flowing through the diode increases sharply with the voltage.
The typical cut-in voltage for a silicon diode is about 0.6 V while a germanium diode has a typical cut-in voltage of about 0.2 V.
A real diode also exhibits some resistance when it is conducting. In fact, the 'on' resistance of a diode is not a fixed value - it roughly varies with the current inversely. A real diode also exhibits a certain amount of current through it when it is reverse-biased. This current is known as its reverse-bias current, or simply reverse current. It is also referred to as 'leakage' current.
If the reverse-bias voltage applied to a diode becomes large enough, the diode junction begins to break down, allowing the diode to conduct even in reverse-bias. This phenomenon occurs at what is known as the reverse breakdown voltage, which is very much larger than the forward cut-in voltage of the diode. For a silicon diode, for instance, the reverse breakdown voltage would be typically around 50 V.
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An ideal diode doesn't conduct any current at all if its cathode is more positive than its anode (or, by convention, the voltage across it is negative). On the other hand, an ideal diode conducts with no resistance at all if the anode is more positive than its cathode (or the voltage across the diode is positive). A diode whose anode is more positive than its cathode is also said to be 'forward-biased', while one whose cathode is more positive than its anode is 'reverse-biased'.
Of course, in the real world, there is no such thing as an ideal diode. A real diode would only start to conduct when the voltage across it exceeds a value referred to as its cut-in voltage (also known as 'break point', 'offset', 'threshold', or 'forward' voltage).
When the diode voltage is below the cut-in voltage, there is almost no current flowing through a diode. Once the diode voltage exceeds the cut-in voltage, the current flowing through the diode increases sharply with the voltage.
The typical cut-in voltage for a silicon diode is about 0.6 V while a germanium diode has a typical cut-in voltage of about 0.2 V.
A real diode also exhibits some resistance when it is conducting. In fact, the 'on' resistance of a diode is not a fixed value - it roughly varies with the current inversely. A real diode also exhibits a certain amount of current through it when it is reverse-biased. This current is known as its reverse-bias current, or simply reverse current. It is also referred to as 'leakage' current.
If the reverse-bias voltage applied to a diode becomes large enough, the diode junction begins to break down, allowing the diode to conduct even in reverse-bias. This phenomenon occurs at what is known as the reverse breakdown voltage, which is very much larger than the forward cut-in voltage of the diode. For a silicon diode, for instance, the reverse breakdown voltage would be typically around 50 V.
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