电容在使用中的注意事项

  • 日期:07-13
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A.什么是好电容器。

1.电容越大越好。

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许多人通常更喜欢在更换电容器时使用大容量电容器。我们知道电容越大,提供给IC的电流补偿能力越强。更不用说电容的增加会增加体积,这会增加成本并影响气流和散热。关键是电容上有寄生电感,电容放电回路会在一定频率下产生共振。在谐振点,电容器的阻抗很小。因此,放电电路的阻抗最小,补充能量的效果也最好。然而,当频率超过谐振点时,放电回路的阻抗开始增加,并且电容器供应电流的容量开始减小。电容器的电容越大,谐振频率越低,并且电容器可以有效地补偿电流的频率范围越小。从确保电容器提供高频电流的能力的角度来看,电容器越大,观点就越差。一般电路设计中有参考值。

2.容量相同的电容器,并联的电容器越小越好

耐压值,耐温值,电容值,ESR(等效电阻)等是电容器的几个重要参数,ESR越低越好。 ESR与电容器的容量,频率,电压和温度有关。当电压固定时,容量越大,ESR越低。在电路板的设计中,使用了许多小电容器,并且连接空间有限。因此,有人认为电阻越多,ESR越低,效果越好。从理论上讲,这是考虑到电容引脚焊点的阻抗,采用多个并联的小电容,效果不一定突出。

3. ESR越低,效果越好。

结合上面改进的电源电路,输入电容具有更大的输入电容容量。相对于容量要求,可以适当降低ESR的要求。因为输入电容主要是耐压,其次是MOSFET的开关脉冲。对于输出电容器,可以适当降低耐压要求和容量。 ESR的要求更高,因为有足够的电流吞吐量得到保证。但是,这里应该注意,ESR不是那么低,而低ESR电容会使开关电路振荡。振动吸收电路的复杂性也导致成本增加。在电路板的设计中,这里通常有一个参考值。这用作元件选择参数,以避免由振动阻尼电路引起的成本增加。

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4.良好的电容代表着高品质。

“只有电容理论”曾经是一个突发事件,一些制造商和媒体也刻意将这件事作为卖点。在电路板设计中,电路设计水平至关重要。一些制造商可以使用两相电源来制造比四相电源更稳定的产品。一些高价电容器不一定能成为好产品。为了测量产品,我们必须考虑所有方面和角度,我们不能有意或无意地夸大电容器的作用。

B.电容器爆炸的面对面访谈

爆破类型:有两种类型,输入电容器爆破和输出电容器爆破。

对于输入电容,我的意思是C1,C1滤除电源接收的电流。输入电容与电源输入电流的质量有关。过大的毛刺电压,高峰值电压,不稳定的电流等会使电容过充电和过放电。在这种工作环境中长时间内,内部温度迅速上升。爆炸将超出通风口的限制。

For the output capacitor, as I said C2, the current adjusted by the power module is filtered. Here, the current is filtered once and is relatively stable, and the possibility of bursting is relatively small. However, if the ambient temperature is too high, the capacitor is also prone to bursting. Explosive, newspaper also. The use of garbage is naturally explosive, retribution. For those who want to know the past, see their present results; for those who want to know the future, see their current causes.

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Reasons for electrolytic capacitor explosion:

There are many reasons for capacitor explosion, such as current is greater than the allowable steady current, the use of voltage exceeds the operating voltage, reverse voltage, frequent charge and discharge. But the most direct cause is high temperature. We know that an important parameter of the capacitor is the temperature resistance value, which refers to the boiling point of the electrolyte inside the capacitor. When the internal temperature of the capacitor reaches the boiling point of the electrolyte, the electrolyte begins to boil, the pressure inside the capacitor rises, and when the pressure exceeds the limit of the venting port, the slurry is exploded. Therefore, temperature is the direct cause of capacitor explosion. Capacitor design has a service life of approximately 20,000 hours and is also greatly affected by ambient temperature. The lifetime of the capacitor decreases with increasing temperature. Experiments have shown that for every 10 °C increase in ambient temperature, the lifetime of the capacitor is halved. The main reason is that the temperature accelerates the chemical reaction and the medium deteriorates with time, so the life of the capacitor is terminated. In order to ensure the stability of the capacitor, the capacitor must pass the long-term high-temperature environment test before inserting the board. Even at 100 ° C, high quality capacitors can work for thousands of hours. At the same time, the life of the capacitor we mentioned refers to the capacitance of the capacitor does not exceed 10% of the standard range change during use. Capacitance life refers to the problem of capacitance capacity, rather than bursting after the design life has arrived. There is simply no guarantee of the capacity standard for the design of the capacitor.

xx所以,短时期内,正常使用的板卡电容就发生爆浆的情况,这就是电容品质问题。另外,不正常的使用情况也有可能发生电容爆浆的情况。比如热插拔电脑配件也会导致板卡局部电路电流、电压的剧烈变化,从而引发电容使用故障。

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