We are in the power supply filter circuit can see all kinds of capacitor
, 100 uf, 10 uf, nf, 100 10 nf different values, so these parameters is how to determine?
50 hz工宽带电路中使用的普通电解电容器,其脉搏电压频率仅为100 hz,充放电时间的毫秒数量级。
Frequency 'features, requires the open within the working frequency power supply should have the equivalent impedance of low, for the work of semiconductor devices at the same time produce high-frequency spike has good filtering effect.
High-frequency aluminum electrolytic capacitor and the form of multicore, the aluminum foil is divided into short segments, with multiple leads connected in parallel to minimize the impedance component of capacitive reactance.
Digital circuit to run stable and reliable, the power must be 'clean' energy supplement, and must be in a timely manner, namely filtering decoupling must be better.
What is a filter for decoupling, a simple say is don't need the chip current storage energy, when you need current I can timely replenish energy again.
Don't talk to me said, 'the duty is not to DCDC? Yes, they can fix in low frequency, but the high-speed digital system are different.
Let's look at a capacitor, capacitance effect of simple said is the storage charge.
We all know to add in the power supply capacitor filter, on each chip power foot placed a 0.
1 uf capacitance decoupling.
And so on, how do I see to some of the power of the chip board feet beside the capacitance is 0.
Uf 1 or 0.
01 uf, what to pay attention to it.
To understand the way way to understand the actual characteristics of capacitance.
And the actual manufactured capacitance is not so simple, analysis of the integrity of the power supply when we commonly used capacitance model as shown in the figure below.
Figure in the ESR is the equivalent series resistance capacitance, ESL is the series equivalent inductance capacitance, capacitance C is the true ideal.
The ESR and ESL is decided by the capacitance of the manufacturing process and material, can't eliminate.
We know that the capacitance of capacitive reactance Zc = 1 / C omega, inductive reactance of inductance Zl = L, omega,
,实时电容性复阻抗为z = esr + jωl -
1 / jωC = ESR + j2πf L -
The effect of capacitance lose filtering.
Mentioned above is the capacitor equivalent series inductance capacitance of manufacturing processes and materials, the actual patch of ceramic capacitor ESL from several tenths of nH to nH, the smaller the encapsulation ESL.
Capacitor filter curve from above we also see that is not flat, it is like a 'V', that is a frequency selective characteristics, in the time we want it to be as flat as possible (
And sometimes hope for it, the more the pointed the better (
Filtering or trap)
Impact of this feature is the capacitor quality factor Q, Q = 1 / omega CESR, ESR, the greater the Q the smaller, the curve becomes more smooth, whereas the ESR is smaller, the greater the Q, the curve becomes more pointed.
In the input stage of DCDC or they often larger capacity of tantalum capacitor filter.
In close to the chip put some 10 uf and 0.
1 uf capacitance to decoupling, ceramic capacitor has a very low ESR.
Said so much, that what we placed near the pin of the chip is 0.
01 uf, the following list for your reference.
So, later don't see what all zero.
1 uf capacitance, some high speed the zero in the system.
1 uf capacitance don't work.
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