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Vacuum Diode ne çi ye?
Pêşnûmayî ya Vacuum Diode
Vacuum diode tiyêkê têkstîn e ku dêrêka strumê elektrîkî yên di navçeya mezin de rêk bêtirîn anod û katod. Katod yek paralelên metelî ye ku bi malî bikar îne ke heta xwarîn elektronan derbas dade, wêken anod yek paralelên metelî bohik e ku elektronan ji katod ve girîng dikin. Sîmol vacuum diode li jêr hatine nîşandan.
Vacuum diode ji aliyê Sir John Ambrose Fleming li sâl 1904 çêkir kiribû û divê hergê valvaya Fleming an valvaya thermionic name kirin. Wekî pirêmîn vacuum tube û pêşînên zeviyên din vacuum tube yên din, wekî triodes, tetrodes û pentodes, ku bi serkeftîn di elektronîk de li virên salemîn 20emîn hatine kar bi kirin. Vacuum diodes bi rengînîn radyoyê, televîzyon, radar, karanîna û hilberdana sese, şebîkeyên telefonê di demên derdîn, û komputerên analog û serdemîn digitalen werdigire.
Prînsip û Karêk
Vacuum diode di prînsip thermionic emission de kerda dike, ku ji surfaceyê metelî yên xwarîn elektronan derbas dade. Ji ber vê yekê, heta katod xwarîn dibêje, elektronan ji navçeyê derbas dibin. Bi vê rêkê, anod bi voltyajê pozitîf elektronan ji katod ve girîng dikin, ku strum ji katod bi anod ên birêk bêtirîn.
Lê, heta voltyaj pozitîf bi anod veguherî ne ku dest bi bash be, anod dikarin hemû elektronan ji katod derbas nikedin, çimke filamên xwarîn. Biceribandin, qandah elektronan di navçeya anod û katod de digerînin, ku bi vê gerîla negativ charge space charge name kirin. Space charge wekî barêrekarî dike ku elektronan ji katod derbas nikibe û strum di cihazê de gir bike.
Heta voltyaj bi anod û katod veguhertî be, zêdetir elektronan ji space charge bi anod girîng dibin û navçeya têkstîn bi elektronan derbasdibinan bêvegir in. Ji ber vê yekê, bi zêdekirina voltyajê ji anod û katod, em dikarin reyê derbasdibina elektronan û bi vê gerîla strum di cihazê de zêde bikin.
Li dema ku hemû space charge bi voltyaj anod neutraliz bikin, tune nekuşîna bêtirîn ji bo derbasdibina elektronan. Li dema ku elektronan bi sedayek ji katod bi anod ên girîng dibin, strum bi anod bi katod ên bi reyê maxîmumê bêtirîn. Reyê maxîmumê vê yekê ji temperatureyê katod ve dipendike. Ev saturation current name kirin.
Di lêgerîn, heta anod bi negativî ji katod biguhezîn, tune derbasdibina elektronan ji anod nabe, çimke anod xwar nabe. Elektronan ji katod derbasdibinan ji ber repulsion negativ anod bi anod nereşin. Space charge bi şaxshiya navçedîn anod û katod digerînin. Bi vê gerîla, elektronan derbasdibinan ji katod bi katod vegerîn, û tune derbasdibin. Ji ber vê yekê, tune strum di cihazê de bêtirîn. Nalazî, vacuum diodes dikarin strum ji katod bi anod ên bêtirîn.
Heta voltyaj bi anod veguhertî ne, idealman tune strum di cihazê de bêtirîn. Lê, bi ragihandina fluctuation ên statistîkî yên velocity electronan, qandah elektronan heta anod reşin. Strum kêmtir ên bi vê gerîla splash current name kirin.
V-I Characteristics
V-I characteristics of a vacuum diode show the relationship between the voltage applied across the anode and the cathode (V) and the current flowing through the circuit (I). The V-I characteristics of a vacuum diode are shown below.
The size of the space charge depends on how many electrons the cathode emits, which is influenced by the cathode’s temperature and work function. The work function is the minimum energy needed to remove an electron from a metal. Metals with lower work functions need less heat to emit electrons, making them more efficient for this purpose.
This region of the characteristics is called the saturation region, as shown in the figure. The saturation current is independent of the anode voltage and depends only on the cathode temperature.
When no voltage is applied to the anode, there should not be any current in the circuit, but in reality, there is a small current due to statistical fluctuations in the velocity of some electrons. Some electrons are energetic enough to reach the anode even when there is no voltage at the anode. The small current caused by this phenomenon is known as a splash current.
Types of Vacuum Diodes
Rectifier diode
Detector diode
Zener diode
Varactor diode
Schottky diode
Applications of Vacuum Diodes
High-power applications
High-frequency applications
High-temperature applications
Audio applications
Conclusion
A vacuum diode is a type of electronic device that controls the flow of electric current in a high vacuum between two electrodes: a cathode and an anode. The cathode emits electrons when heated by a filament or an indirect heater, while the anode collects electrons from the cathode. The vacuum diode works on the principle of thermionic emission and allows current to flow only in one direction: from cathode to anode.
Vacuum diodes were invented by Sir John Ambrose Fleming in 1904 and were widely used in electronics for the first half of the 20th century. They were essential for the development of radio, television, radar, sound recording and reproduction, long-distance telephone networks, and analog and early digital computers. Vacuum diodes have been replaced by semiconductor diodes in most applications, due to their smaller size, lower power consumption, higher reliability, and lower cost. However, vacuum diodes are still used in some areas where they have advantages over solid-state devices, such as high-power, high-frequency, high-temperature, and audio applications.
Vacuum diodes can be classified according to different criteria, such as frequency range, power rating, cathode/filament type, application, specialized parameters, and specialized functions. Some examples of vacuum diode types are rectifier diodes, detector diodes, zener diodes, varactor diodes, and Schottky diodes.
The vacuum diode is a simple but important device that has played a significant role in the history and development of electronics. It is still relevant today for some applications that require its unique characteristics and performance. The vacuum diode is a testament to the ingenuity and innovation of electronic engineers and scientists who have explored the possibilities and potentials of vacuum tubes.
