Unsa ang Vacuum Diode?

Ano ang Vacuum Diode?

Pahayag ng Vacuum Diode

Ang vacuum diode usa ka tipo sa electronic device nga kontrola ang pagtumong sa electric current sa taas nga vacuum tali sa duha ka electrodes: ang cathode ug anode. Ang cathode usa ka metal cylinder nga gipalabhan og materyales nga mag-emisyon og electrons kapag init, samantalang ang anode usa ka hulog nga metal cylinder nga nag-collect og electrons gikan sa cathode. Ang simbolo sa vacuum diode makita sa ubos.

Ang vacuum diode gihimo ni Sir John Ambrose Fleming sa 1904 ug nailhan usab isip Fleming valve o thermionic valve. Kini ang unang vacuum tube ug ang precursor sa uban pang vacuum tube devices sama sa triodes, tetrodes, ug pentodes, nga giwasto sa electronics sa unang bahin sa ika-20 siglo. Importante ang vacuum diodes alang sa pag-develop sa radio, television, radar, sound recording ug reproduction, long-distance telephone networks, ug analog ug early digital computers.

Prinsipyong Operasyon

Ang vacuum diode operasyon batasan sa thermionic emission, diin ang electrons gipadala gikan sa init nga metal surface. Kapag init ang cathode, ang electrons moka-abot sa vacuum. Ang positibong voltage sa anode natra siya sa mga electrons, padayon ang current mula sa cathode tungod sa anode sa usa ka direksyon.

Pero kung ang positibong voltage nga gipadayon sa anode wala sulay, ang anode wala maka-attract sa tanang electrons gikan sa cathode tungod sa init nga filament. Taliwala ang electrons nag-accumulate sa espasyo tali sa cathode ug anode, formando ang cloud of negative charge nga gitawag og space charge. Ang space charge nag-act isip barrier nga nag-prevent sa mas daghan nga emission of electrons gikan sa cathode ug nag-reduce sa current flow sa circuit.

Kapag ang applied voltage tali sa anode ug cathode gradual nga na-increase, mas daghan pa ang space charge electrons gipadayon sa anode ug create vacant space para sa mas daghan nga emitted electrons. So sa increase of voltage across the anode and cathode, kita mahimo ang increase sa emission rate of electrons ug hence ang current flow sa circuit.

Sa usa ka punto, kung ang tanang space charge neutralized sa anode voltage, wala na gyud obstruction for electron emission from the cathode. Then a beam of electrons starts flowing freely from the cathode to the anode through space. As a result, current flows from the anode to the cathode at its maximum value, which depends only on the temperature of the cathode. This is called saturation current.

Sa lahi-lahi, kung ang anode gipang-negative tali sa cathode, wala gyud emission of electrons gikan sa anode tungod sa cold, dili hot. Ngayon, ang emitted electrons gikan sa heated cathode wala maabot sa anode tungod sa repulsion sa negative anode. A strong space charge will be accumulated between the anode and cathode. Due to this space charge, all further emitted electrons are repelled back to the cathode, and hence no emission takes place. Therefore, no current flows in the circuit. So, vacuum diodes allow current to flow in one direction only: from cathode to anode.

Kapag wala gyud voltage gipadayon sa anode, ideally, wala gyud current. Pero tungod sa statistical fluctuations sa velocity sa electrons, ang uban pa gyud maabot sa anode. Kini nga small current known as splash current.

V-I Characteristics

Ang V-I characteristics sa vacuum diode show ang relationship tali sa voltage gipadayon sa anode ug cathode (V) ug ang current flowing through the circuit (I). The V-I characteristics of a vacuum diode are shown below.

Ang size sa space charge depende kung pila ka electrons ang cathode emits, nga influenced sa cathode’s temperature ug work function. Ang work function usa ka 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.