The Birth of a Capacitor
Time：2021.10.09
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The Birth of a Capacitor
In 1746, the physicist Massenbruck of Leiden University in the Netherlands invented a "condenser" capacitor with power storage function. Since the capacitor was born in the Dutch city of Leyden, people called it "Leyden jar", which began the history of human use of capacitors.
The invention of the Leyden bottle provides an effective method for the scientific community to store electricity, provides a new and powerful means for further in-depth study of electrical phenomena, and plays an important role in the dissemination and development of electrical knowledge.
The improved Leiden bottle at that time was like this. The inner and outer walls of the glass bottle were pasted with metal foil, and a metal rod was inserted into the top cover of the Leiden bottle. Its upper end was connected to a metal ball, and its lower end passed through. The metal chain is connected to the inner wall. In this way, the Leiden bottle is actually an ordinary capacitor. If its outer wall is grounded and the metal ball is connected to a charge source, a considerable amount of charge will accumulate between the inner and outer walls of the Leiden bottle. When the Leiden bottle is discharged, a considerable current can pass.
How capacitors work: water towers as a metaphor
In a sense, capacitors are a bit like batteries. Although the two work in completely different ways, they can both store electrical energy. However, the principle of a capacitor is much simpler than that of a battery, and it cannot generate electrons-it just stores electrons. Like batteries, capacitors also have two electrodes. Inside the capacitor, the two electrodes are connected to two metal plates separated by a dielectric. The dielectric can be air, paper, plastic, or any other non-conductive substance that prevents the two metal poles from contacting each other.
The capacitor in the electronic circuit is shown in the figure:
Let us see what happens when we connect the capacitor and the battery together:
After charging, the capacitor has the same voltage as the battery (if the battery voltage is 1.5 volts, the capacitor voltage is also 1.5 volts). Small capacitors have lower capacity, but large capacitors can hold a large amount of charge. For example, a capacitor the size of a soda can can hold enough charge to light a flashlight bulb for several minutes. When you see lightning in the sky, what you see is a huge capacitor. One pole is the dark cloud in the sky, and the other pole is the earth. The lightning is between the two "poles" of the dark cloud and the earth. The phenomenon of charge release. Obviously, such a huge capacitor can hold a lot of charge!
Below, let us assume that you connect the capacitor to the circuit as follows:
You have a battery, a light bulb, and a capacitor. If the capacitor is very large, then you will see that after the battery is connected, current flows from the battery to the capacitor to charge it, and the bulb will be lit at this time. The bulb will gradually dim, and finally, once the capacitor reaches its capacity, the bulb will immediately go out. Later, you can remove the battery and replace it with a piece of wire. Current will flow from one pole of the capacitor to the other. At this time, the light bulb will be bright again, but the good times will not last long, and the light bulb will gradually dim again soon. Finally, the capacitor is discharged (the number of electrons on the two poles of the capacitor are equal), and the bulb goes out again.
In summary, the function of a capacitor can be described visually with a water tower connected to a water pipe. Water towers can be used to "store" water pressure-when the water supply system pumps supply more water than the town needs, the excess water will be stored in the water tower. Then, when the water demand is high, the excess water will flow out of the water tower to maintain the water pressure. Capacitors store electrons in the same way and can release them later. This is how the capacitor works.
Capacitor's physical business card
In the International System of Units, the unit of capacitance is Farah, abbreviated as law, and the symbol is F. Commonly used capacitance units are millifarad (mF), microfarad (μF), nanofarad (nF) and picofarad (pF) (picofarad) Also known as Pico Method) etc.,
The conversion relationship is:
1 Farad (F) = 1000 millifarads (mF) = 1000000 microfarads (μF)
1 microfarad (μF) = 1000 nanofarad (nF) = 1000000 picofarad (pF)
Related formulas:
For a capacitor, if the potential difference between the two levels is 1 volt with 1 bank of electricity, the capacitance of this capacitor is the 1 method, that is: C=Q/U, but the size of the capacitance is not determined by Q or U, that is: C =εS/4πkd. Among them, ε is a constant, S is the area of the capacitor plate, d is the distance between the capacitor plates, and k is the electrostatic force constant.
Several applications of capacitors
Storage battery: This function is used by the flash. Large lasers also use this technology to obtain very bright instant flash effects.
Eliminate pulsation: If the line that conducts DC voltage contains pulsation or spikes, the large-capacity capacitor can smooth the voltage by absorbing the crests and filling the troughs.
Block DC: If a smaller capacitor is connected to the battery, after the capacitor is charged (when the capacitor has a small capacity, the charging process can be completed instantly), there will be no more current flowing between the two poles of the battery. However, any alternating current (AC) signal can flow through the capacitor unimpeded. The reason is that as the alternating current fluctuates, the capacitor is continuously charged and discharged, as if the alternating current is flowing.
Oscillation circuit: used with inductors: constitute an oscillator.
Capacitor
一. Classification according to structure
Fixed capacitors, variable capacitors and trimmer capacitors.
二. Classified by electrolyte
Organic dielectric capacitors, inorganic dielectric capacitors, electrolytic capacitors and air dielectric capacitors, etc.
三. Classification by purpose
1. High frequency bypass: ceramic capacitors, mica capacitors, glass film capacitors, polyester capacitors, glass glaze capacitors.
2. Low frequency bypass: paper capacitors, ceramic capacitors, aluminum electrolytic capacitors, polyester capacitors.
3. Filtering: aluminum electrolytic capacitors, paper capacitors, composite paper capacitors, liquid tantalum capacitors.
4. Tuning: ceramic capacitors, mica capacitors, glass film capacitors, polystyrene capacitors.
5. High frequency coupling: ceramic capacitors, mica capacitors, polystyrene capacitors.
6. Low frequency coupling: paper capacitors, ceramic capacitors, aluminum electrolytic capacitors, polyester capacitors, solid tantalum capacitors.
7. Small capacitors: metalized paper capacitors, ceramic capacitors, aluminum electrolytic capacitors, polystyrene capacitors, solid tantalum capacitors, glass glaze capacitors, metalized polyester capacitors, polypropylene capacitors, mica capacitors.
The "legend" of supercapacitors
principle
The capacity of supercapacitors is much larger than that of ordinary capacitors. Because of its large capacity and the same external performance as a battery, it is sometimes called a "capacitor battery". Supercapacitors are electric double-layer capacitors. They are the largest electric double-layer capacitors that have been put into mass production in the world. The basic principle is the same as other types of electric double-layer capacitors. They are composed of activated carbon porous electrodes and electrolyte. The electric double layer structure obtains a large capacity.
Features
1. The charging speed is fast, charging for 10 seconds to 10 minutes can reach more than 95% of its rated capacity;
2. Long cycle life, the number of deep charge and discharge cycles can reach 1 to 500,000 times, and there is no "memory effect";
3. Super high current discharge capacity, high energy conversion efficiency, low process loss, high current energy cycle efficiency ≥90%;
4. High power density, up to 300W/KG~5000W/KG, equivalent to 5~10 times of battery;
5. The product raw material composition, production, use, storage and dismantling process are free of pollution, which is an ideal green and environmentally friendly power source;
6. Simple charging and discharging circuit, no need for charging circuits like rechargeable batteries, high safety factor, maintenance-free for long-term use;
7. Good ultra-low temperature characteristics, wide temperature range -40℃～+70℃;
8. The detection is convenient, and the remaining power can be read directly;
9. The capacity range is usually 0.1F--1000F.
The future of capacitors
With its many advantages, super capacitors have been predicted by various media to represent the future development direction of new energy batteries, and the author greatly agrees. With the introduction of multi-touch screens on the Apple iPhone in 2007, capacitive touch technology can be said to have a bright future, and capacitive touch controllers that meet various qualification requirements have also emerged. Because capacitive touch has higher light transmittance and resolution than resistive touch, and can multi-finger touch input function (resistive touch can only be a single finger), the service life is longer than resistive touch, capacitive touch Technology will become the mainstream of technology. Because resistive touch screens can still remain in the market for a while because of their low cost, but as long as the cost of capacitive touch modules decreases and the production yield rate increases, the capacitive touch module market is bound to threaten the future Replace the resistive touch market position.
