Diode
What's diode
A diode is a two-terminal device that allows current to flow in one direction, known as the forward direction, when the anode of the diode has a higher positive potential than the cathode. In this state, the diode is said to be forward biased. If the polarity of the voltage is reversed, the diode is now reverse biased, and it will attempt to block current flow, within its rated limits. Diodes are often used as rectifiers to convert alternating current into direct current. They may also be used to suppress voltage spikes or protect components that would be vulnerable to reversed voltage, and they have specialized applications in high-frequency circuits.
A Zener diode can regulate voltage, a varactor diode can control a high-frequency oscillator, and
tunnel diodes, Gunn diodes, and PIN diodes have high-frequency applications appropriate to their
rapid switching capability. An LED (light-emitting diode) is a highly efficient light source, which is
discussed in other article. A photosensitive diode will adjust its ability to pass current depending on the light that falls upon it,
A Zener diode can regulate voltage, a varactor diode can control a high-frequency oscillator, and
tunnel diodes, Gunn diodes, and PIN diodes have high-frequency applications appropriate to their
rapid switching capability. An LED (light-emitting diode) is a highly efficient light source, which is
discussed in other article. A photosensitive diode will adjust its ability to pass current depending on the light that falls upon it,
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| Figure 26-1. diode symbols |
The basic diode symbol is modified in various ways to represent variants, as shown in Figure 26-2.
At top : Each symbol in the group of six indicates a Zener diode. All are functionally identical.
Bottom-left : Tunnel diode.
Bottom-center : Schottky diode.
Bottom-right : Varactor.
A triangle with an open center does not indicate any different function from a triangle with a solid center. The direction of the arrow always indicates the direction of conventional current, from positive to negative, when the diode is forwardbiased, although the functionality of Zener diodes and varactors depends on them being reverse-biased, and thus they are used with current flowing opposite to the arrow symbol. The bent line used in the Zener symbol can be thought of as an opened letter Z, while the curled line used in the Schottky diode symbol can be thought of as a letter S, although these lines are sometimes drawn flipped left-to-right.
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| Figure 26-2. Commonly used schematic symbols for specialized types of diodes. |
A range of rectifier and signal diodes is shown in Figure 26-3. (Top: Rectifier diode rated 7.5A at 35VDC. Second from top: Rectifier diode rated 5A at 35VDC. Center: Rectifier diode rated 3A at 35VDC. Second from bottom: 1N4001 Rectifier diode rated 1A at 35VDC. Bottom: 1N4148 signal switching diode rated at 300mA.) All values are for forward continuous current and RMS voltage.
Each cylindrical diode is marked with a silver stripe (a black stripe on the 1N4148) to identify its cathode, or the end of the diode that should be “more negative” when the component is forward
biased. Peak current can greatly exceed continuous current without damaging the component. Datasheets will provide additional information.
+to+300mA+.jpg "Diodes ranging in continuous forwardcurrent capability") |
| Figure 26-3. Diodes ranging in continuous forwardcurrent capability from 7.5A (top) to 300mA |
