For CLC and CRC filtering, it is best to have high-frequency capacitors at both ends of the resistor and inductor. Could you please tell me how to configure the high-frequency capacitors?

snowblind123

For CLC and CRC filtering, it is best to have high-frequency capacitors at both ends of the resistor and inductor. Could you please tell me how to configure the high-frequency capacitors? [Copy link]

 

For CLC and CRC filtering, it is best to use high-frequency inductors at both ends of the resistor and inductor, and then connect them to electrolytic capacitors. If both ends are electrolytic, it will introduce noise from the inductor and resistor.

The combination of high-frequency capacitor 0.1uf + large-capacity high-frequency capacitor has the lowest noise. Could you please tell me how to configure the high-frequency capacitor?

chunyang

This statement is problematic. There is no such thing as "electrolytic capacitors at both ends will cause noise from inductance and resistance", and a 0.1uF capacitor cannot be considered a "high-frequency capacitor".

What the original poster said should be the power supply filtering under normal circumstances. Whether the 0.1uF decoupling capacitor is necessary must be analyzed based on the load and the previous power supply. In addition, in common low-voltage power supply circuits, CLC, especially CRC filtering, is rarely used now.

se7ens

CRC is equivalent to a C plus an RC filter, and the effect is limited

maychang

"If the two ends are electrolytic, it will cause noise from inductance and resistance."

This is because the electrolytic capacitor electrode foil is wound, and there are internal parasitic inductance and internal parasitic resistance. When AC current flows through the capacitor, it will of course generate voltage on this parasitic inductance and parasitic resistance. Whether it is necessary to connect high-frequency capacitors in parallel depends on the specific situation.

他们逼我做卧底

chunyang published on 2022-5-19 13:00 This statement is problematic. There is no such thing as "electrolytic capacitors at both ends will cause noise from inductance and resistance". A 0.1uF capacitor is not considered a &ld ...

What kind of filtering method is used in common low-voltage power supply circuits nowadays?

maychang

They forced me to be an undercover agent. Published on 2022-5-19 15:22 What kind of filtering method is used in the common low-voltage power supply circuit now?

"What kind of filtering method is used in the common low-voltage power supply circuit nowadays?"

A low-power, low-voltage power supply is usually a flyback switching power supply, which uses only one electrolytic capacitor at its output.

chunyang

They forced me to be an undercover agent. Published on 2022-5-19 15:22 What kind of filtering method is used in the common low-voltage power supply circuit now?

In most cases, electrolytic capacitor filtering is sufficient, and 0.1uF decoupling capacitors are placed next to sensitive devices in digital devices or mixed analog and digital circuits.

snowblind123

maychang published on 2022-5-19 16:09 "What kind of filtering method is used in the common low-voltage power supply circuit now? 】 Low-power low-voltage power supply is usually a flyback switching power supply, which...

Why does TI's reference design use high-frequency capacitors like this? I don't understand.

snowblind123

maychang published on 2022-5-19 16:09 "What kind of filtering method is used in the common low-voltage power supply circuit now? 】 Low-power low-voltage power supply is usually a flyback switching power supply, which...

Why does TI's reference design use high-frequency capacitors like this? I don't understand.

snowblind123

chunyang posted on 2022-5-19 16:15 In most cases, electrolytic capacitor filtering is sufficient, and 0.1uF decoupling capacitors are placed next to sensitive devices in digital devices or mixed analog circuits.

Why do TI reference designs have high frequency capacitors regardless of power?

maychang

snowblind123 posted on 2022-5-20 13:43 Why does TI's reference design use high-frequency capacitors like this? I don't understand

On the 6th floor, I said that "usually" only one electrolytic capacitor is used. On the 7th floor, Chunyang said "in most cases". That means there are exceptions.

Chunyang on the 7th floor said "0.1uF decoupling capacitors are placed next to sensitive devices in digital devices or mixed analog circuits". The picture you posted only shows a small-capacity capacitor placed at the power output. There must be several small-capacity capacitors next to the power-consuming chips. Doing so will of course reduce the ripple, but the cost will definitely increase.

maychang

snowblind123 posted on 2022-5-20 13:43 Why does TI's reference design use high-frequency capacitors like this? I don't understand

The second picture you posted uses two resistors, one R1 is 100k and one R2 is 1.0k.

snowblind123

maychang posted on 2022-5-20 13:56 On the 6th floor, I said that "usually" only one electrolytic capacitor is used. On the 7th floor, chunyang said "in most cases". ...

A lot of high-frequency capacitors are used in power frequency rectification filtering and input. How are these capacities obtained? The cost is increased by a few cents. Why is it that people rarely use high-frequency capacitors for input and output filtering? I have never seen anyone use 0.1uf.

chunyang

snowblind123 posted on 2022-5-20 13:55 Why do TI reference designs basically have high-frequency capacitors regardless of power?

If you look at it more, you will find that what you said about "all have" is a minority of cases, and it is obvious that the statement of "all have" is not valid. Even in your several figures, not all of them are CLC and CRC filter structures.

When to use it requires specific analysis of the specific situation, and the circuit noise and load sensitivity must be examined. The reason why it is said "in most cases..." is that it is not used based on the circuit noise and load sensitivity. Just like someone wears a sheepskin coat, and in some places even many people wear sheepskin coats, but you can't say that this is what humans should wear every day. There are summer clothes and winter clothes. Even in winter, sheepskin coats are not necessarily the only clothes to wear.

maychang

snowblind123 posted on 2022-5-20 14:20 A large number of high-frequency capacitors are used in power frequency rectification filtering and input. How are these capacities obtained? The cost is only increased by a few cents, so why do we lose...

"A large number of high-frequency capacitors are used in power frequency rectification, filtering, and input."

I have never seen "a large number of high-frequency capacitors" used at the input of a power frequency rectifier filter. Can you take a look at the picture?

snowblind123

chunyang posted on 2022-5-20 14:23 If you look more closely, you will find that what you said about "both" are rare cases. Obviously, the statement that "both" are not true...

These manufacturers' reference designs basically have high-frequency capacitors. I have visited several forums and have never seen anyone use high-frequency capacitors. I think the "few cases" are because they don't know how to use them. I have disassembled many power supplies and they do not have high-frequency capacitors on the input and output. Strictly speaking, these power supplies are not qualified and have great noise interference, but they will not break down. Some of the inputs in the above pictures are CLC structures

chunyang

snowblind123 posted on 2022-5-20 14:35 These manufacturers' reference designs basically have high-frequency capacitors. I have visited several forums and have never seen one that uses high-frequency capacitors. "A few...

Your conclusion is too hasty, and you won't think so in a few years. Pay attention to what I said in the previous post - the circuit noise and load sensitivity must be examined.

snowblind123

chunyang posted on 2022-5-20 14:50 Your conclusion is too hasty. You will not think so in a few years. Pay attention to what I said in the previous post - it is necessary to examine the circuit noise and...

Why not? A few ceramic capacitors, just a few cents more cost, not only noise and load, maybe in a few years I won't think so, anyway, I think few people in the world will use high-frequency capacitors, including big companies like Apple, except for chip manufacturers like TI.

snowblind123

maychang posted on 2022-5-20 14:31 "A large number of high-frequency capacitors are used in the input of the power frequency rectifier filter." I have never seen a large number of high-frequency capacitors used in the input of the power frequency rectifier filter...

It's in the picture above.

chunyang

snowblind123 posted on 2022-5-26 10:30 Why not? A few ceramic capacitors, just a few cents more cost, not only noise and load, maybe in a few years I won't think so, anyway, I think...

Knowing when to use it, when not to use it, and the reasons behind it, is the real skill.