We would are inclined to take the phrase “diode” without any consideration if we’re pondering of a “diode” as only a two-lead or two-terminal system that will get used on this or that place for this or that goal. It could possibly change into a bit humbling to ponder simply what number of varieties of diodes we even have at our disposal and what they’re used for.
Let’s take a quick, if super-simplistic, look. The schematic symbols proven for every case should not the one relevant symbols I’ve ever seen. In some instances, there are image variations in use, however these few proven right here will simply should suffice for now.
1. Rectifier Diode (energy, sign)
It is a system that merely carries {an electrical} present in a single course and blocks present stream within the different course. It may be a small and acquainted system just like the 1N4148 or one thing fairly huge like a 1N4045 275A 100-V rated diode for a bridge rectifier for wind turbine generator service, or larger nonetheless. It can be a bit of pencil lead touching a rusty razor blade, a stiff wire (a cat’s whisker) making some extent contact on a block of galena, or a low-power, point-contact germanium diode just like the 1N34A.
2. Schottky Diode (scorching service)
This type of diode is made by forming a junction between a steel (many several types of steel can be utilized) and a few semiconductor materials. It has the benefit of a decrease ahead voltage drop than a semiconductor-to-semiconductor diode and little or no storage cost, leading to a very quick turn-off time.
3. Step Restoration Diode
This system is a semiconductor-to-semiconductor diode with a helpful quantity of saved cost that permits a quick conduction time within the reverse course. Time issues proper and you’ll trigger the reverse conduction to halt on the 270° level of an enter RF sinusoid when the storage cost very abruptly runs out. Extraordinarily abrupt present halts make this system a very nice harmonic generator in frequency multiplier functions.
4. PIN Diode (P-type semiconductor, intrinsic semiconductor, N-type semiconductor)
This system is a semiconductor-to-semiconductor diode with a helpful quantity of saved cost that permits intentional conduction time within the reverse course. For prime sufficient frequencies, sometimes 1 GHz and up, this diode’s dynamic impedance could be various by controlling the DC bias present. That variable impedance is beneficial for making programmable sign attenuators.
5. Picture Diode
A photograph diode will generate {an electrical} output in response to stimulation by mild. Some units may even be used to detect ultraviolet and/or X-rays.
6. Gentle Emitting Diode (LED)
A lightweight-emitting diode will generate mild in response to stimulation by {an electrical} present. Some diode units can generate seen mild, as pink, yellow, amber, inexperienced, blue, or white, whereas others can generate infrared or ultraviolet. My dentist makes use of a hand-held ultraviolet LED mild to hurry up the setting strategy of dental cement. I questioned him about that. He used to reveal dental cement to an ultraviolet lamp.
7. Laser Diode
A laser diode makes use of a PIN diode construction to pump the intrinsic area within the heart of that diode into laser motion inside an optical cavity. Certainly one of this stuff is hiding inside that laser pointer of yours, and one other one is in your CD participant.
8. Zener Diode
A Zener diode is an strange diode, however one whose reverse voltage attribute has a intentionally low breakdown threshold. There’s little or no present stream via the Zener diode in response to the appliance of a reverse bias voltage till that reverse bias voltage will get excessive sufficient to cross the breakdown threshold and induce a considerable present stream. Voltage regulation is a sensible software of this impact.
9. Transient Absorbing Diode
A transient-absorbing diode may be very very similar to a Zener diode, however with the power to face up to transient intervals of excessive energy throughout breakdown. Safety of digital circuitry from in any other case damaging voltage transients is the sensible goal of those units.
10. Again Diode
A again diode is a diode whose reverse breakdown threshold may be very low, even decrease than the ahead voltage drop of different diodes and even decrease than the ahead voltage drop of the again diode itself. Low-level RF detection is the sensible software for these units.
11. Varactor Diode
A varactor diode is a diode that’s usually operated with reverse voltage utilized. The capacitance throughout the reverse-biased system varies inversely with the utilized reverse bias voltage. RF tuning, particularly the tuning of voltage-controlled oscillators, is the most typical sensible goal of those units.
12. Tunnel Diode (Esaki)
Tunnel diodes are diodes whose voltage versus present attribute is discontinuous. They’ve “voltage-controlled damaging resistance” properties. As I personally recall, they have been invented in 1957 and have been as soon as thought to herald a brand new age in semiconductor know-how. Heathkit even made a tunnel diode DIP oscillator, superseding its earlier grid dip oscillator product. Right now, tunnel diodes are nonetheless accessible, though not too generally used.
13. Gunn Diode
Gunn diodes are single-material semiconductors with no PN junction; however, they exhibit a damaging resistance property that may be exploited to make a microwave oscillator. The dearth of a PN junction makes some people object to the phrase “diode” as a descriptor for these units, however the time period has change into a widely known colloquialism, so who am I to attempt to change issues?
14. Present Limiting Diode
This system may not be known as a “diode” both, however as with the Gunn diode, there’s a generally used colloquialism. This system can be a junction discipline impact transistor (JFET) with the gate tied to the supply. The voltage versus present attribute curve is that of a JFET with Vgs of zero, which, when the system is pulled out of JFET saturation by a sufficiently excessive voltage, behaves as a relentless present driver.
15. Vacuum Diode (Sure, we’re taking a look at tubes too.)
We could have come full circle at this level. This system is thermionic and, similar to its solid-state counterparts, it would conduct present solely in a single course. Assume 5Y3GT and 35Z5GT. If these half numbers don’t look acquainted, go forward and look them up.
16. Mercury Vapor Diode
A detailed cousin to the vacuum diode, these units have an inside environment of heated mercury. The truth is, you must enable sufficient time (60 seconds if I recall appropriately) for the filament to make the mercury scorching sufficient to change into a vapor earlier than you attempt to press the diode into precise service. Additionally, the system should be operated solely within the vertical place with the bottom pins on the backside and the plate cap on high. When this tube is doing its factor, the ionized mercury glows blue. Consider the 866A, and once more, if that half quantity doesn’t look acquainted, go forward and look it up.
17. Xenon Gasoline Diode
One other vapor-dependent diode, however this time the environment is xenon. There isn’t a must warmth the xenon earlier than use, as it’s already a fuel. When this tube is doing its factor, the ionized xenon glows a considerably yellowish-white coloration. Consider the 3B28 and once more, if that half quantity doesn’t look acquainted, go forward and look it up.
18. Magnetron
A magnetron is basically an informed vacuum tube diode used for producing microwave alerts. (Please see “Magnetron.”)
19. Chilly Cathode Gasoline Voltage Regulator
This system isn’t usually known as a “diode”, nevertheless it meets my thought of being one. It’s crammed with an ionizable fuel, which, when it does get ionized, the plate-to-cold-cathode voltage tends to be secure. It’s rather a lot like a zener diode in that sense, nevertheless it has one troublesome trait of which to bear in mind. The “putting voltage” for which ionization begins is sort of a bit greater than the regular state voltage beneath regular state fuel ionization. That yields a damaging resistance property, which, when you put capacitance in parallel with this system, yields leisure oscillation. When this tube is doing its factor, its fuel has a violet glow. Assume 0A2 (That first character is a numeral zero, not a letter “oh”.) and but once more, if that half quantity doesn’t look acquainted, go forward and look it up.
I simply occur to have a type of readily available:
20. Mogen Diode
An imaginary system dreamed up by the late Bob Pease. No additional dialogue needed.
John Dunn is an electronics marketing consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York College (MSEE).
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