First, applied to the power circuit, to achieve bypass, to lotus, filter and energy storage capacitor role.
The following classification details:
Filtering is a very important part of the role of CBB80 Lighting Capacitor . Almost all of the power circuit will be used. From the theory (that is, assuming that the capacitor is pure CBB80 Lighting Capacitor ), said the larger the CBB80 Lighting Capacitor , the smaller the impedance, the higher the frequency. But in fact more than 1uF capacitor mostly electrolytic capacitors, there is a lot of inductance components, so the frequency is high but the impedance will increase.
Sometimes see a capacitor with a larger CBB80 Lighting Capacitor in parallel with a small capacitor, then a large capacitor through low frequency, small CBB80 Lighting Capacitor through high frequency. The role of the capacitor is through the high resistance low, high frequency resistance through the high frequency. The larger the CBB80 Lighting Capacitor , the easier it is to pass the lower frequency, and the higher the CBB80 Lighting Capacitor , the easier it is to pass. Specifically used in filtering, large CBB80 Lighting Capacitor (1000uF) filter low frequency, small CBB80 Lighting Capacitor (20pF) filter high frequency.
Have friends will filter capacitor compared to "reservoir". As the voltage at both ends of the capacitor does not change, we can see that the higher the signal frequency is the greater the attenuation, the image can be said that a capacitor like a pond, will not be due to a few drops of water to join or evaporation caused by changes in water. It changes the voltage into the current changes, the higher the frequency, the greater the peak current, thus buffering the voltage. Filtering is the process of charging and discharging.
The bypass capacitor is an energy storage device that provides energy to the local device, which can equalize the output of the regulator and reduce the load demand. Like a small rechargeable battery, the bypass capacitor can be charged and discharged to the device. To minimize the impedance, the bypass capacitor should be as close as possible to the load device's power supply pin and ground pin. This can well prevent ground potential elevation and noise due to excessive input values. The ground is a ground drop at a voltage drop when passing through a high current glitch.
3) to lotus root
To lotus, also known as lotus root. From the circuit, it is always possible to distinguish between the driven source and the driven load. If the load CBB80 Lighting Capacitor is relatively large, the drive circuit to charge the capacitor, discharge, in order to complete the signal transition, in the rising edge of the steep time, the current is relatively large, so the drive current will absorb a large supply current, Of the inductor, the resistance (especially the chip pin inductance, will produce a rebound), this current relative to the normal situation is actually a noise, will affect the normal work of the previous level. This is coupling.
To the lotus capacitor is to play a role in the battery to meet the current changes in the drive circuit to avoid the coupling between the interference. Combining the bypass capacitor with the decoupling capacitor will be easier to understand. Bypass capacitor is actually to the coupling, but the bypass capacitor is generally refers to the high-frequency bypass, that is, to the high-frequency switching noise to improve a low impedance leakage path.
High-frequency bypass capacitors are generally relatively small, according to the resonant frequency is generally 0.1u, 0.01u, etc., and decoupling capacitors are generally larger, is 10uF or greater, according to the distribution parameters in the circuit, and the drive current to determine the size of the change. Bypass is the interference in the input signal as the filter object, and decoupling is the output signal interference as a filter object to prevent the interference signal back to power. This should be their essential difference.
4) energy storage
The energy storage capacitor collects the charge through the rectifier and transfers the stored energy through the converter lead to the output of the power supply. Aluminum electrolytic capacitors (such as EPCOS B43504 or B43505) with voltage ratings of 40 to 450 VDC and CBB80 Lighting Capacitor values between 220 and 150 000 uF are more commonly used. Depending on the power requirements, the device may be in series, in parallel, or in the form of a combination. For power sources with a power level of more than 10 kW, a larger tank-type screw terminal capacitor is typically used.
2, applied to the signal circuit, the main completion of the coupling, oscillation / synchronization and the role of time constant:
For example, the transistor amplifier emitter has a self-bias bias resistor, which also makes the signal pressure drop to the input to form the input and output signal coupling, this resistance is to produce a coupling element, if the resistance in the two Side of a capacitor in parallel, due to the appropriate capacity of the capacitor on the AC signal smaller impedance, thus reducing the resistance generated by the coupling effect, so called the capacitor for the decoupling capacitor.
2) oscillation / sync
Including RC, LC oscillator and crystal load CBB80 Lighting Capacitor belong to this category.
3) Time constant
We know the role of the capacitor after the following to talk about
Capacitor in the use of the precautions
A. What is a good capacitor?
(1) the greater the CBB80 Lighting Capacitor the better.
Many people in the replacement of capacitors often love to use large-capacity capacitors. We know that the greater the CBB80 Lighting Capacitor , the stronger the ability to provide current compensation for the IC. Not to mention the increase in the capacity of the capacitor to bring the volume larger, increase the cost of the same time also affect the air flow and heat. The key lies in the existence of parasitic inductance on the capacitor, the capacitor discharge circuit will resonate at a certain frequency. At the resonant point, the impedance of the capacitor is small.
So the impedance of the discharge circuit is minimal, the effect of supplemental energy is also the best. But when the frequency exceeds the resonance point, the impedance of the discharge circuit began to increase, the capacitor capacity to provide current capacity began to decline. The larger the CBB80 Lighting Capacitor of the capacitor, the lower the resonant frequency, the smaller the frequency range that the capacitor can effectively compensate for the current. From the perspective of the ability to ensure that the capacitor provides high frequency current, the bigger the CBB80 Lighting Capacitor is, the better the point of view is that the general circuit design has a reference value.
(2) the same capacity of the capacitor, the more parallel the smaller the better CBB80 Lighting Capacitor
Pressure value, temperature, value, ESR (equivalent resistance) is a few important parameters of the capacitor, the ESR is naturally the lower the better. ESR and CBB80 Lighting Capacitor of the capacity, frequency, voltage, temperature and so have a relationship. When the voltage is fixed, the larger the capacity, the lower the ESR. In the board design using a number of small capacitors and even more with the PCB space constraints, so that some people think that the more parallel the small resistance, ESR lower, the better the effect. Theoretically, but to take into account the resistance of the capacitor pin solder joints, the use of multiple small capacitors in parallel, the effect is not necessarily prominent.
(3) ESR lower, the better the effect.
In combination with our improved power supply circuit above, the input CBB80 Lighting Capacitor is larger for the input CBB80 Lighting Capacitor . Relative capacity requirements, the requirements of the ESR can be appropriately reduced. Because the input capacitor is mainly voltage, followed by the MOSFET to absorb the switching pulse. For the output capacitor, the pressure requirements and capacity can be appropriately reduced a little. ESR requirements are higher, because here to ensure that the amount of sufficient current through. But here to note that the ESR is not as low as possible, low ESR capacitor will cause the switch circuit oscillation. And the complexity of the vibration circuit will lead to an increase in cost. Board design, there is generally a reference value, which as a component selection parameters, to avoid the vibration circuit caused by the increase in costs.
(4) a good capacitor represents a high quality.
"Only CBB80 Lighting Capacitor theory" was flourishing, some manufacturers and the media also deliberately put this thing into a selling point. In the board design, the circuit design level is the key. And some manufacturers can use two-phase power supply than some manufacturers to use four-phase power supply more stable products, blindly using high-priced capacitors, not necessarily make good products. Measure a product, must be all-round multi-angle to consider, must not be the intention of the capacitor intentionally exaggerated.
B. Capacitor blasting face interview
Explosive pulp types: divided into two categories, the input capacitor burst and the output capacitor burst pulp.
For the input capacitor, that is, I said C1, C1 received by the power supply to filter the current. The input capacitor is related to the quality of the input current. Excessive burr voltage, peak voltage is too high, the current is not stable and so the capacitor is too frequent charge and discharge over a long time in such a working environment of the capacitor, the internal temperature rise soon. Above the discharge limit of the discharge will occur burst pulp.
For the output capacitor, I said C2, the power module after the adjustment of the current filter. Here the current through a filter, more stable, the possibility of occurrence of explosive pulp is relatively small a lot. But if the ambient temperature is too high, the capacitor is also prone to burst pulp. Burst, reported also. The use of garbage things to burst, retribution ah. For those who are in the past, see their present fruit;
Electrolytic capacitor burst pulp reasons:
Capacitor burst pulp for many reasons, such as the current is greater than the allowable steady wave current, the use of voltage beyond the operating voltage, reverse voltage, frequent charge and discharge. But the most straightforward reason is high temperatures. We know that the capacitor has an important parameter is the temperature value, refers to the capacitor inside the electrolyte boiling point. When the internal temperature of the capacitor reaches the boiling point of the electrolyte, the electrolyte begins to boil, and the internal pressure of the capacitor rises. When the pressure exceeds the bearing limit of the discharge port, So that the temperature is the direct cause of the capacitor burst pulp.
Capacitor design life of about 20,000 hours, affected by the ambient temperature is also great. Capacitor life with the increase in temperature decreases, the experiment proved that the ambient temperature for each rise of 10 ℃, the capacitor life will be halved. The main reason is that the temperature to accelerate the chemical reaction leaving the media degradation over time failure, so that the end of the capacitor life. In order to ensure the stability of the capacitor, the capacitor in the board before going through a long period of high temperature environment test. Even at 100 ℃, high-quality capacitors can work thousands of hours.
At the same time, we mentioned the life of the capacitor is the capacitor in the use of the process, the CBB80 Lighting Capacitor capacity will not exceed 10% of the standard range changes. CBB80 Lighting Capacitor life refers to the problem of CBB80 Lighting Capacitor capacity, rather than the design life arrived after the occurrence of explosive pulp. Just can not guarantee the CBB80 Lighting Capacitor of the design capacity standards.
Therefore, a short period of time, the normal use of the board capacitor on the case of explosive pulp, which is the capacitor quality problems. In addition, the abnormal use of the situation may also occur in the case of explosive powder. Such as hot-swappable computer accessories will lead to local circuit board current, voltage changes, resulting in capacitor failure.
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