34
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 ...
- 443k
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/...
- 707
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 ...
- 383k
17
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 ...
16
votes
Accepted
Ripple voltage filtering capacitor
I've included a snapshot, of sorts, so that you can see what's happening better:
On the main diagram, I expanded out a rectangle and placed it over to the right side so that you might see a little ...
- 77.4k
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, ...
- 71.9k
14
votes
Accepted
How to filter out the switching noise from a DC/DC converter
The Measurement Technique
As mentioned in the comments by some of the folks, the first thing I would make sure is appropriate is the measurement technique. Measuring power supply noise accurately ...
- 5,574
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 ...
- 23.4k
13
votes
Accepted
How to know if this is a band-pass filter?
Long way around the barn, but I'll get there....
Sallen & Key: "A Practical Method of Designing RC Active Filters"
I want to start out by reflecting on the TR-50 paper by R. P. Sallen &...
- 77.4k
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}...
- 170k
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. ...
- 383k
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 ...
- 20.9k
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.
- 137k
9
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 ...
- 31.3k
9
votes
How to filter out the switching noise from a DC/DC converter
After receiving so many good answers, I started to test them all. This is my report.
Input inductor should be as close to the IC as possible
(Comment by Lars Hankeln)
The inductor was definitively ...
- 1,043
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 ...
- 78k
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 ...
- 443k
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 ...
- 162k
8
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:
...
- 77.4k
8
votes
How to know if this is a band-pass filter?
For this particular circuit, you know that there must be some mid-band frequency that does pass, because there is some frequency where
$$j\omega L = -\frac{1}{j\omega C}$$
and therefore the impedance ...
- 128k
7
votes
Accepted
Loading effect of two stages of RC filter
You have come up with an equation without thinking much about the circuit. When you have two RC pairs cascaded, as a passive filter, you will have the following circuit:
simulate this circuit – ...
- 2,644
7
votes
Why, in a passive circuit with a sinusoidal input, do all voltages and currents have the same sinusoidal behavior as the input?
It happens because a sinewave is just one line in the frequency spectrum and no matter what you do with it using a linear filter or amplifier, all that happens is that the phase or amplitude shifts.
...
- 443k
7
votes
Low Pass Filter Wrong Pole Location
It's just a conversion from radians to degrees. The expression for a capacitor's impedance uses units of radians/sec. for frequency. The simulator is reporting frequencies in Hertz. 10 rad/sec is 1....
- 2,580
7
votes
How to filter out the switching noise from a DC/DC converter
I'll try to solve as many problems as I can before going to the first PCB.
Except... most of the problems you have are due to the assembly technique. It is entirely inappropriate for the application.
...
7
votes
How to know if this is a band-pass filter?
I'm not able to tell if it passes mid-range frequencies or not.
Well, you were nearly there with your first line of algebra that produced this: -
$$Z_{parallel} = \dfrac{jωL}{1−ω^2LC}$$
The next step ...
- 443k
7
votes
How to know if this is a band-pass filter?
I will start with an intuitive explanation: At DC the capacitance is an open-circuit, while the inductor is a short, hence \$v_o=0V\$. At very high frequencies the inductor will act as an open-circuit,...
- 1,367
7
votes
Accepted
What is this following filter circuit called? (For amplifiers)
The way the capacitors are currently drawn is a bit confusing, and reflects their physical wiring rather than their actual configuration.
It is helpful to redraw the circuit slightly, so the two ...
- 18.8k
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 ...
- 4,028
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 ...
- 1,870
Only top scored, non community-wiki answers of a minimum length are eligible