Is inductance or magnetic beads used to isolate the digital power supply from the analog power supply?

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Is inductance or magnetic beads used to isolate the digital power supply from the analog power supply? [Copy link]

 

 

Is inductance or magnetic beads used to isolate the digital power supply from the analog power supply?

chunyang

Generally, magnetic beads can be used, which are cheaper.

bigbat

It is related to the load change of your circuit. If the load is relatively stable, use magnetic beads, and if the load changes greatly, use inductors.

lugl4313820

It is related to the load change of your circuit. If the load is relatively stable, use magnetic beads, and if the load changes greatly, use inductors.

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Gen_X

The current is small and it is just isolation at higher frequencies, so the ferrite beads are sufficient.

RC was also used in the past.

wangerxian

chunyang published on 2022-10-12 17:13 Generally, magnetic beads can be used, which is cheaper.

Do inductors and magnetic beads have the same function? Are they just used in different environments?

bigbat

Magnetic beads have a strong ability to block high-frequency DC. Inductors have a relatively large "inductance" and poor DC passing ability. They can block interference signals with large current changes. However, they can also cause circuit oscillations. This is not conducive to the operation of analog signals. Inductors must have a large capacitance to absorb voltage.

chunyang

wangerxian posted on 2022-10-13 09:18 chunyang posted on 2022-10-12 17:13 Generally, magnetic beads can be used, and the price is lower. Do inductors and magnetic beads have the same function? It's just that the use environment...

Please note that ferrite beads are a type of inductor, so your statement is logically invalid and cannot be explained this way at all.

wangerxian

chunyang posted on 2022-10-13 12:11 Note that magnetic beads are a type of inductor, so your statement is not logically valid and cannot be said at all.

So in what situations can magnetic beads be used?

chunyang

wangerxian posted on 2022-10-13 13:06 So in what situations can magnetic beads be used?

The essence of magnetic beads is an inductor, which is characterized by a wide operating spectrum and low price, but the inductance is unstable. Not only is the manufacturing discreteness large, but it is also a function of frequency. Therefore, magnetic beads are not used in traditional inductor applications, such as LC oscillators, but are mainly used to suppress high-frequency noise. Here, the large eddy current loss of magnetic bead inductors is utilized. It is for this reason that magnetic bead inductors are listed separately and are not classified as traditional inductors in general contexts. Therefore, they are called "magnetic beads" and their nominal values are also expressed in "ohms", that is, equivalent impedance, rather than "henry", that is, inductance.

chunyang

As mentioned in the original post, stringing a magnetic bead in the power supply circuit of the digital part and the power supply circuit of the analog part is a typical application - high-frequency noise suppression. The signal edge of the digital circuit will generate a lot of noise, that is, an ideal square wave is composed of a sine wave of the same frequency plus its infinite harmonics of each order. Digital noise may affect the normal operation of the analog circuit, especially the analog circuit with micro-signals and high gain. If the power supply is directly connected, the noise generated by the digital circuit will affect the analog circuit through the coupling of the power supply circuit. At this time, a magnetic bead is strung between the power supply circuits of the analog circuit and the digital circuit. According to the characteristics of the magnetic bead - the higher the frequency of the signal, the greater the loss through the magnetic bead (in a quadratic function relationship), the high-order harmonic noise generated by the digital circuit is absorbed by the magnetic bead, thereby reducing the impact of digital noise on the analog circuit. Of course, magnetic beads are used more in signal circuits, also to suppress high-frequency noise. In addition, magnetic beads can also be used in dealing with ESD, in conjunction with ESD suppression components, one is blocking (the role of magnetic beads) and the other is sparse (TVS, clamping diodes, small capacitors, etc.).

qwqwqw2088

Isolation of digital power and analog power

The essence is the isolation between digital ground and analog ground

The original poster should ask whether the isolation between the digital ground and the analog ground is a ferrite bead or a 0 ohm resistor.

wangerxian

chunyang posted on 2022-10-13 13:29 The essence of magnetic beads is an inductor, which is characterized by a wide working spectrum and low price, but the inductance is unstable. Not only is the manufacturing discreteness large, but the frequency...

I see. I used magnetic beads in previous projects, but I didn't know that the inductor symbol was the so-called magnetic beads. Now I understand.

chunyang

wangerxian posted on 2022-10-13 14:11 I understand. I used magnetic beads in previous projects, but I didn’t know that the inductor symbol used the so-called magnetic beads. Now I understand.

As mentioned before, magnetic beads are a type of inductor. Of course, the inductor symbol must be used in the circuit diagram, but the parameters must be expressed in ohms. When you see an inductor in ohms, you naturally know that it is a magnetic bead.

chunyang

qwqwqw2088 posted on 2022-10-13 13:51 The isolation between digital power supply and analog power supply is essentially the isolation between digital ground and analog ground. The original poster should ask about the isolation between digital ground and analog ground...

This is indeed referring to the power supply loop rather than the ground loop. Magnetic beads may not be used to isolate ground loops, but it is very common to use magnetic beads to isolate power supply loops.

吾妻思萌

Magnetic beads, 0Ω resistors, and inductors are all OK, but they are more expensive.

fjdeepblue

Generally, magnetic beads are used, and the characteristics of magnetic beads and inductors are different.