Chapter I: Basic Components
Resistance, the English name of resistance, often abbreviated as R, which is one of the basic nature of the conductor, and conductor size, material, temperature. Ohm's law says, I = U / R, then R = U / I, the basic unit of resistance is the
Impede current flow. In fact, the "resistance," says a character in the electronic products are usually referred to the resistance means that such a resistor element. Master of the apprentice, said: "Find a 100-ohm resistor to!" Refers to a "resistance" as the 100 ohm resistor, Ohm's often referred to as Europe. Said resistor are commonly used unit of Europe 1000 (kΩ), megohm (MΩ).
First, the type of resistor
There are many types of resistors are usually divided into three categories: fixed resistors, variable resistors, special resistance. In electronic products, up to a fixed-resistor applications. And the fixed resistor can be divided into a lot of material for its manufacturing category, but commonly used, there is a common RT-type carbon film resistors, RJ-type metal film resistor, RX-type wound resistors, there are widely used in recent years began to sheet resistance. Model Naming is very laws, R on behalf of resistance, T-carbon film, J-metal, X-wound, is the first letter of alphabet. Old electronic products in the domestic, they often can see the appearance of the resistance of coated masking, that is, RT type. The red color of the resistance, is the RJ type. Old electronic products in general, the resistance of green majority. Why? This involves the product cost problem, because although the high precision metal film resistors, temperature characteristics of good, but manufacturing costs are also high, while the carbon film resistors special low price, but also to meet the requirements of civilian products.
Of course, there are power resistors divided. Common are 1 / 8 watt "color ring carbon film resistors", which is the electronics and electronics manufacturing using the most. Of course, in a number of micro-products, will use 1 / 16 watt resistor, and its tall, little more. Furthermore, is the mini-sheet resistance, which is the family of a patch element, previously more common in imports of micro-products, are now electronic enthusiasts can also buy the (wireless listening device to do?)
Second, the identification resistor
These direct labeling of the resistance, in the new bought, it is very easy to identify specifications. However, in the assembly of electronic products, steps must be taken into account for future maintenance of the convenience, to mark towards the easy-to-face to see places. Therefore, when the foot bend, with particular attention. In the manual assembly, multi-working procedure that is not a big problem, but automatic production line machines are not that clever. Moreover, the resistor components getting smaller and smaller, direct labeling of the tag is difficult to see. Therefore, the international practice, "Color Ring mark law." In fact, the "color ring resistance" occupy a resistor element of the mainstream. "Color ring resistance," the name suggests, is to use different colors on the resistor ring to represent the resistance specifications. Some are said to use four-color rings, and some with 5. Different from Yao? Yes. 4 ring resistance, generally carbon film resistors, with the three-color rings to represent resistance, using a color wheel that error. 5 rings are generally resistance metal film resistors, in order to better express precision, using four-color ring, said resistance, and the other color ring is also said that error.
Color ring resistance on behalf of the rules is the last lap error, for the four-ring resistance, before the second ring on behalf of RMS, the third ring on behalf of the th power multiplied by the number. Do not be afraid, remember the color and digital on-line 啦, others do not mind. There is a secret: the face of a color ring resistance, find gold or silver at one end, and it is down, from scratch, reading color rings. For example, the first ring is brown, and the second link is black, the third ring is red, the fourth ring is gold, then its resistance value is 1,0, the third ring is the number of Tim zero, this Resistance 2 Tim zero, so it is the actual resistance is 1000Ω, the 1kΩ.
3, variable resistor
, Also known as variable resistor potentiometer, electronic equipment on the volume potentiometer is a variable resistor. However, are generally considered potentiometer can be manually adjusted, while the variable resistors are generally small, often mounted on the circuit board is not adjustable. Variable resistor has three pins, two of which the value of a fixed resistor between the pins, and that the resistance value is called the variable resistor. The third pin with any resistance value between the two pins you can arm with the axis of rotation change. In this way, the circuit can adjust the voltage or current, to adjust results.
4, special resistance
Photosensitive resistance is a resistance to outside light intensity (shade) and change the components, the smaller the light the stronger the resistance, light resistance of the weaker the greater. Its shape and the circuit symbol shown in Figure 2. If Photoresistor pins of two pens connected to the multimeter on the table, with a multimeter R × 1k block the light of measurements in different photosensitive resistance is: The photosensitive resistance to move from the dark in a drawer under the sun or lighting , the meter reading will change. In complete darkness Department, the photosensitive sheet resistance of up to a few megohm or more (infinite resistance multimeter instructions, that the pointer does not move), while in strong light, the resistance can be reduced to a few thousand or even a 1000 Europe Europe following.
With this feature, you can create a variety of light control of a small circuit. Most street lights in fact run out of control switch automatic control, and one of the important components is the light-sensitive resistor (or a photosensitive three tubes, a feature similar to the semiconductor device with amplification). Photosensitive resistor is deposited on the ceramic base layer of cadmium sulfide (CdS) film made of, actually a kind of semiconductor components. The new village, voice-activated lights in the daytime will not be lit corridor, but also because photosensitive resistance at work. We can use it to produce electronic herald the break of chicken in the morning when dawn WoWo call.
Thermistor is a special semiconductor devices, and its resistance value as its surface temperature changes in the level of change. It was originally is to enable electronic devices in different environmental temperatures to work properly used, is called temperature compensation. The new motherboard has a CPU temperature, over-temperature alarm function is to use a thermistor.
Electronics manufacturing need to use a wide variety of capacitors, which, respectively, in the circuit play different roles. Similarity with the resistor, usually referred to it as capacitance, with the letter C, said. As the name suggests, the capacitor is "Charge storage containers." Despite the wide variety of capacitors, but their basic structure and principles are the same. Two pieces of metal in close proximity middle of a substance (solid, gas or liquid) by separated, would constitute a capacitor. Two plates of metal known as the intermediate material called the dielectric. Capacitor is also divided into a fixed capacity and capacity variable. But the common is a fixed-capacity capacitor, electrolytic capacitor is the most common and porcelain capacitors.
Different capacitor charge storage capacity is not the same. To provide for plus 1 volt DC voltage capacitors when the charge amount stored in the capacitor is called capacitance. The basic unit of capacitance Farah (F). But in fact, Farah is a very popular unit, because the capacity of capacitors are often much smaller than a Farah, often microfarads (μF), sodium Act (nF), PF (pF) (pF also known as pico-France ), etc., their relationship is this: 1 farad (F) = 1000000 microfarads (μF) 1 microfarads (μF) = 1000 nF (nF) = 1000000 pF (pF)
In the electronic circuit, the capacitor is used through the exchange while blocking DC, is also used to store and release charge in order to act as a filter, smoothing the output pulse signal. Small-capacity capacitor, usually the use of high-frequency circuits, such as radios, transmitters and oscillator. Large-capacity capacitor is often used for filtering and storage charge. But also a feature of the general 1μF capacitors are electrolytic capacitors above, while the 1μF capacitor below mostly porcelain capacitors, of course, there are also other, such as monolithic capacitors, polyester capacitors, mica capacitors of small capacity. There is aluminum electrolytic capacitors, which is full of electrolytes, and leads to two electrodes, as a positive (+), negative (-) pole, and other capacitors, unlike those in the circuit can not pick the wrong polarity, while the other capacitors are there is no polarity.
The two capacitor electrodes were connected to the power of positive and negative, on a moment even if the power disconnect between the two pins will still be residual voltage (after school tutorials, you can use multimeter observation), we say capacitor stored charge. Established between the capacitor plate voltage, savings from energy, a process known as the capacitors charge. Capacitor charge at both ends of the wires have a certain voltage. The charge storage capacitor to the circuit release procedure, known as the capacitors discharge.
Give a real-life examples, we see commercially available rectifier power supply after you unplug and plug the above light-emitting diodes will continue to light for a while, and then gradually extinguished, it is because the capacitance inside the pre-stored energy, and then released. Of course, this was originally used as a filtering capacitor. As for the capacitor filter, I wonder if you have no use Rectifier Walkman to listen to the experience, the general low quality of power supply due to cost savings for manufacturers to consider using a smaller capacity of the filter capacitor, resulting in a buzzing sound in headphones. At this time in power at both ends and connected to a large-capacity electrolytic capacitor (1000μF, attention to positive then positive), generally improve performance. HiFi stereo enthusiasts production, we must use at least 1 million micro-method above to filter capacitor, filter capacitor greater the output voltage waveform closer to DC, and the role of large energy storage capacitors, making sudden arrival of large-signal, the circuit there is sufficient energy is converted to a strong powerful audio output. At this time, a bit like the role of large reservoir capacitors, making the original output of the turbulent flow smoothly, and can guarantee that when the lower reaches of a large number of water supply.
Electronic circuit, only in the capacitor charging process, the only current flowing through the charging process is completed, the capacitor is a DC can not, in the circuit acts as a "DC-blocking" role. Circuit, capacitors are often used for coupling, bypass, filtering and so on, are using it, "Link exchange, DC-blocking" features. So Why is alternating current through capacitor do? Let's take a look at the characteristics of alternating current. Alternating back and forth not only the direction of alternating current, its size is also changed according to the law. Capacitor connected to the AC power, the capacitor continuously charged and discharged, the circuit will flow with the alternating current changes of the same charge current and discharge current.
Capacitor Selection involves many problems. The first is pressure problem. Added to both ends of a capacitor voltage exceeds its rated voltage, capacitor breakdown will be damaged. Voltage electrolytic capacitors generally sub-file for the 6.3V, 10V, 16V, 25V, 50V, etc..
Inductor in the electronic production although the use was not very large, but they are in the circuit are equally important. We believe that the inductors and capacitors, just as a kind of energy storage components, it can power into a magnetic field can, and store energy in a magnetic field. Used for symbol inductance L said it was the basic unit is the Henry (H), commonly used millihenry (mH) as a unit. It is often and capacitors to work together, constitute the LC filters, LC oscillators. In addition, it is also the use of inductance properties, creating a choke ring, transformers, relays, etc..
Precisely the characteristics of inductors and capacitors feature the contrary, it has to stop alternating current to direct current through the adoption of features.
On the radio there are a lot of small inductance coil, almost all with the enameled wire around the coil into the hollow core or in the skeleton, on the winding core made of. An antenna coil (which is used enameled wire wound on the magnetic bar made of), intermediate frequency transformer (commonly known as the weeks), input and output transformers and so on.
Physical map and the circuit symbols shown in Figure
Transformer is in the insulation around the core and the skeleton on the composition of the copper coil wire. Insulated copper wire wrapped around the plastic frame, each frame needs two sets of input and output winding coil. Isolation between the coil with the insulating paper. Will be around a good number of core sheets inserted in the plastic skeleton in the middle. This enables the coil inductance was significantly increased. Transformers use electromagnetic induction principle from one of its winding windings to another child transmission of electric energy. Transformer in a circuit that has important functions: coupling AC signal while blocking DC signals, and can change the input and output voltage ratio; the use of transformer impedance of the circuit to be a good match at both ends in order to maximize the transmission signal power.
High-voltage power transformers is to become a civilian electricity, while many of our electrical appliances are using the low-voltage DC power supply to work, need to use power transformer to 220V AC electricity transform into a low-voltage alternating current, and through the diode rectifier, capacitor filter, the formation of DC power supply work. TV picture tubes require tens of thousands of volts to work, is a "line output transformer," the supply.
Of course, the power transformer has its many flaws, such as power and volume is proportional to heavy, low efficiency, and now being a new type of "electronic transformer" replaced. Electronic transformer is generally "switching power supply", the computer requires several groups of voltage is the switching power supply, and color TV, the display is in use, without exception, switching power supply.
Electromechanical relay is a switch, it is enamelled copper wire in a circle around the core on the hundreds of thousands of ring to ring, mid-stream when the coil over-current, the circular iron core produces a magnetic field, the upper core band Circle contact with iron tablets Xi Zhu, so that the first contact and turned off the second switch contacts. When the coil power, the core loss of magnetic properties, due to the flexibility of the role of contact with copper to make iron from iron core to restore the contact with the first one connected. Therefore, we can use a small current to control the other circuit switching. The entire relay made of plastic or plexiglass dust cover protects some or all sealed to protection against electric shock oxidation.