32 votes
Accepted

Active low-pass filters --- good to what frequencies?

I believe your analysis to be good. I've made sallen-key 4th order filters that cut-off around 3 MHz with absolutely no worry about performance. I don't see that 10 MHz is unachievable. It's all ...
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  • 378k
24 votes
Accepted

Why, in a passive circuit with a sinusoidal input, do all voltages and currents have the same sinusoidal behavior as the input?

I've been pouring my brains out and eventually I've found a nice mathematical approach to prove this and decided to answer my own question. In such a circuit, solving for any voltage/current across/...
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20 votes
Accepted

What is the reason to connect 4 resistors of the same value as 2s2p? (image)

Dissipation (4x) or pulse power capability (4x) since cost can go up much faster than those capabilities— or redundancy (no single failure will cause a short or open). The latter strategy is used in ...
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15 votes
Accepted

Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?

is there any disadvantage of using a high-value resistor with a low-value capacitor or vice versa? Yes. High impedance brings to mind: High-value resistors create high-impedance nodes. That wouldn't ...
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14 votes

What is the reason to connect 4 resistors of the same value as 2s2p? (image)

As the others have said, it's most likely about dissipation and pulse power. But there is also cost. If you already have a reel of 10R chip resistors of one value loaded on the pick and place machine, ...
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  • 57.5k
13 votes

In terms of costs of mass production: is it better to try to reduce resistances' tolerance or capacitors' tolerance?

Generally it is much cheaper to get tight tolerance resistors than capacitors. You might find that even 5% resistors are mostly within 1% since the manufacturing process for resistors has become very ...
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  • 19.5k
12 votes
Accepted

How to create large inductors (1H) for audio use?

The primary of a smallish power transformer is on the order of 1 H. Magnetizing current for such a transformer is on the order of 0.35 A, which means that its inductive impedance is $$Z = \frac{V}{I}...
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  • 164k
11 votes

Why, in a passive circuit with a sinusoidal input, do all voltages and currents have the same sinusoidal behavior as the input?

This is only true for LTI (Linear Time-Invariant) circuits. If you have a non-ideal component (and they all are to one degree or another) you will see harmonics of the input frequency in the output. ...
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11 votes

What is meant by filter order of a passive filter?

The order of a circuit depends on the polynomial degree of its denominator. That degree itself depends on the number of independent state variables. State-variable are associated with energy-storing ...
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10 votes

What is the reason to connect 4 resistors of the same value as 2s2p? (image)

Four smaller and cheaper resistors that can dissipate less can be used instead of single larger and more expensive resistor that can dissipate more.
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  • 87.1k
8 votes

RC Lowpass Filter between Amplifier and ADC input

If you are reading the ADC just once per second then you need to eliminate frequencies above 0.5 Hz to prevent aliasing. If you think your system will have noise at, say 10 Hz, then that noise will ...
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8 votes

Active low-pass filters --- good to what frequencies?

My first question: really? A mere 100kHz is already too high for active filters to be practical? No, 100kHz is nothing, but it all depends on the opamp. At some point the Gain Bandwidth Product is ...
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  • 63.3k
8 votes

High capacitance C0G (NPO) capacitor

I need to build a LC high-pass filter that \$\color{red}{\text{cuts at 30 kHz}}\$ with a fixed L value of 2.5 µH. As the cut-off frequency is 1/sqrt(LC), that means I need a capacitance of 440µF to ...
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  • 378k
8 votes

Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?

What you're talking about is choosing the impedance of the filter. If you were operating the filter between a zero source impedance and an infinite load impedance, then you would be completely free to ...
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  • 140k
7 votes

Why, in a passive circuit with a sinusoidal input, do all voltages and currents have the same sinusoidal behavior as the input?

It happens because a sinewave is just one line in the frequency spectrum and no matter what you do with it using a linear filter or amplifier, all that happens is that the phase or amplitude shifts. ...
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  • 378k
7 votes

Low Pass Filter Wrong Pole Location

It's just a conversion from radians to degrees. The expression for a capacitor's impedance uses units of radians/sec. for frequency. The simulator is reporting frequencies in Hertz. 10 rad/sec is 1....
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  • 2,530
7 votes

Passive RC filter second order with resistors in parallel - How to calculate the cutoff frequency?

Symbolic analysis with KCL I'll add my own tidbit. Using the freely available SymPy tool: ...
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  • 68.9k
6 votes
Accepted

Loading effect of two stages of RC filter

You have come up with an equation without thinking much about the circuit. When you have two RC pairs cascaded, as a passive filter, you will have the following circuit: simulate this circuit – ...
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6 votes

Why, in a passive circuit with a sinusoidal input, do all voltages and currents have the same sinusoidal behavior as the input?

The basic reason is that the constituent equations of ideal R, L and C components are linear, time invariant equations involving only derivatives and integrals (both linear operations) and that sine ...
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6 votes
Accepted

Parallel RC filter on SCR gate

R2 is a "gate-cathode resistor". Visually, the schematic makes it look like R2 is about C2, but it's really about the SCR's performance. A gate-cathode resistor allows some of the SCR anode current ...
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  • 1,850
6 votes

How to create large inductors (1H) for audio use?

They were wound like transformers, as Dave Tweed mentioned. But they were of specific construction that is different from typical power transformers: the laminations were thinner, so they would be ...
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  • 35.8k
6 votes

Why does the capacitor need to be small in RC filter circuits?

Basically, lower valued capacitors can use dielectric materials that have better performance. Less variability due to temperature and bias voltage. Less variability over time. Higher working voltage ...
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  • 121k
6 votes
Accepted

Derive the transfer function

I use a concept of outflowing and inflowing currents, which is how Spice programs develop their matrices as well, when developing my KCL equations. I place the first on the left side and the second on ...
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  • 68.9k
6 votes

Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?

Accurate, stable, high quality signal capacitors can be expensive, difficult to find, or outright not available. Often 100nF is the upper limit and that's already stretching it. Really high value ...
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  • 46k
6 votes

Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?

The general trend is: Higher resistor, smaller cap: less load on source, higher output noise, potentially reduced output voltage if load impedance is low. Small resistor, large cap: less noise and ...
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  • 10.2k
6 votes

Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?

You select filter components not "according to ... wish" but to meet the transfer function specifications. On board Resistors For opamp based circuits: ...
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  • 1,131
6 votes

Is there any advantage or disadvantage of using high value capacitor instead of high value resistor in filter?

In many cases, there is another restriction which will cause additional selection limits. Keyword: Component spread. All second-order filter stages require a minimum of 2 resistors and 2 capacitors ...
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  • 22.5k
6 votes
Accepted

Can I attenuate ripple noise from a R-78E3.3-0.5 with an LC filter?

Is perhaps the R-78E3.3-0.5 a bad choice in my application because I only draw 10mA of its potential 500mA. Would the R-78E3.3-0.5 produce a higher (and thus easier to attenuate) ripple frequency in ...
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  • 378k
6 votes

What is the reason to connect 4 resistors of the same value as 2s2p? (image)

Sometimes that configuration is used to protect against failures in the 4 resistor network, compared to a single resistor. If you have a single resistor, the primary failure modes are 1) an open or 2) ...
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  • 7,169

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