A capacitor, usually ceramic, used to provide instantaneous energy to a local circuit.

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96 views

Decoupling a power supply

I'm building my first biped robot, using a Raspberry Pi as the brain. My problem is, I want to decouple the battery before I use it to power the Pi. The reason I want to decouple the battery is ...
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2answers
72 views

Op Amp Decoupling with a Virtual Ground

I'm designing a low-frequency op. amp. circuit that operates from a single 10V supply. I'm using a TLE2426 "rail-splitter" to generate a virtual ground, 5V above earth ground, which is used as a ...
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1answer
48 views

Review and question about AD9838 circuit

I have tried to come up with a schematic of using AD9838. I used the eval. board schematic and modified it to my needs. The eval. board schematic can be found on page 9 here: AD9838 eval. board ...
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1answer
144 views

Decoupling Arduino's power supply

I am building a replacement for dishwasher's controller that burned, using Arduino Leonardo. Arduino is powered through standard 9V AC/DC converter. Dishwasher uses quite large 220VAC electric pump ...
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1answer
80 views

Are there flaws in the reasoning behind the Zedboard bypass scheme?

There is an eval board for the Xilinx Zynq-7000 FPGA called the Zedboard. When you look at the board you will notice a very interesting pattern of bypass capacitors. The designer has a technical note ...
2
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1answer
119 views

Norton Equivalent of Capacitively Coupled LRC Circuit

The diagram below is a schematic representation of a microwave lumped element notch filter. The goal is to analyse the parallel LRC circuit and derive an expression for \$S_{21}(\omega)\$, where port ...
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3answers
1k views

Why need the capacitors be as close as possible to the device?

Just a simple question: what exactly stands behind the need for placing the capacitors as close as possible to the current consuming device's pins? Is that the inductance, resistance or maybe ...
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3answers
571 views

“two bypass/decoupling capacitors” rule?

I found many discussions on bypass capacitors and their purpose. Usually, they come as a pair of 0.1uF and 10uF. Why does it have to be a pair? Does anyone have a good reference to a paper or an ...
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4answers
141 views

When to use film capacitor

I've bought a bunch of film type capacitor as they were pretty cheap and I thought it was a good idea to get some and test them. (set here) So I'm trying to figure out what's the specific application ...
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1answer
204 views

Crystal, PCB Layout

I've completed a few circuit board layouts before, however this is my first time doing a layout with a oscillator/MCU. After doing some reading (via this site and datasheets) I've come up with the ...
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1answer
164 views

Smoothing and decoupling power source input

I am transforming an old battery-only radio so I can connect it through a DC input. I found an earlier model diagram that includes the DC input (picture attached). I have connected a 18 V DC source ...
4
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2answers
270 views

Does my circuit need decoupling caps? [duplicate]

I have a very simple design that I'm now working on the PCB layout for. And at the moment I'm thinking about the issue of decoupling capacitors. The board is very simple and only consists of this: ...
3
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1answer
136 views

Why would I need AC coupling if audio inputs already do the job?

I'm transmitting data from a microcontroller to a smarphone mic input and I was suggested to use this circuit to adapt the 5v digital signal: Taken from this tutorial The way I see it R2 and R3 ...
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3answers
217 views

Can two devices share a decoupling capacitor?

I am working on a circuit that has two devices that are each supposed to have decoupling capacitors. In this case however, the devices are right next to each other, and their power supply pins are ...
2
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3answers
207 views

Can multiple decoupling capacitors be replaced with a single low-inductance type?

It seems to be usual practice to put in decoupling capacitors of several different values, for example 0.1uF and 1uF (or sometimes 10uF, or 0.01uF depending on the device etc). I'm wondering if there ...
4
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1answer
94 views

Procedure for experimentally determining decoupling capability?

I'm looking for a bullet-point list of a technique to experimentally determine a design's decoupling capability. I have a design that I'm working on that seems to be susceptible to ESD events in the ...
3
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1answer
86 views

Changing decoupling capacitor values

I'm building a small board that uses the MMA8453Q Freescale Accelerometer. The datasheet requires a 4.7μF decouple capacitor on the \$V_{dd}\$ pin. I only have 3.3μF or 6.8μF capacitors on ...
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0answers
118 views

How can I find a super low ESR ceramic 0805 capacitor for FGPA bypass?

This is a super boring question, but I'm stuck. I'm ordering the BOM for an FPGA board I designed a while back. The xilinx application notes state that I need a capacitor with the following ...
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1answer
80 views

through hole or SMD capacitor for high voltage powers [closed]

When TH and SMD caps are avalilable with same spec, which one to prefer for high voltage powers.?
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3answers
924 views

Calculating the value of bypass capacitors for an amplifier

I want to know if there is a rough any ready way of calculating the capacitance required to decouple the power supply used in an amplifier. (Rough and ready because I'll be adding 30% to the value ...
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1answer
68 views

Switch (dis)connects an LDO regulator from VBATT. Where should the filter cap go?

In my system, there are several DC-DC regulators all attached to a VBATT unregulated rail. One of the regulators is the LDO shown in the picture below. The user can connect it and disconnect it from ...
13
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4answers
2k views

How to place decoupling capacitor in four-layer PCB?

I searched a technology document about placement of decoupling capacitors and the main idea is shown in the following picture: I think it is reasonable but do I have to put the decoupling capacitor ...
3
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4answers
367 views

Do I need filtering caps for a USB power supply?

I'm pulling 5V from USB for testing an IC. Should I put a capacitor in there to filter the power supply, or will it already be steady coming from the laptop? I don't have access to an oscilloscope, ...
4
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1answer
110 views

Substition of electrolytic capacitors in surface mount applications

I understand there are advantages and disadvantages against using electrolytic capacitors over others, such as ceramic, but from what I understand the main reason of choosing electrolytic caps is ...
3
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1answer
125 views

Is this a polarised capacitor

So I went to a local electronics retailer, Communica in Cape Town yesterday. I had a small shopping list including: 10x 10µF Ceramic Capacitor 10x 0.1µF Ceramic Capacitor The vendor didn't have ...
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2answers
167 views

parallel decoupling capacitors

In my circuit , I need decoupling capacitors , but my local shop doesn't have some values like 300nf so I need to put in parallel 3 of 100nf . the equivalent CAP would be 300nf but with multiple ...
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1answer
798 views

Reducing LED PWM Noise: Which is the best option?

Driving an LED with a microcontroller should be easy. But when looking into noise, things can get complex... As an instantaneous voltage indicator used in a variable power supply (which will be used ...
7
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1answer
412 views

Placement/routing of decoupling cap straddling oscillator guard ring on dsPIC

Changes in my design are forcing me to replace my 44-pin dsPIC33FFJ16MC304 with a 64-pin (same package size, finer pin pitch) dsPIC33FJ64MC506. In the datasheets for both chips, Microchip recommends a ...
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1answer
749 views

Sensor decoupling and noise reduction

I have an Arduino UNO board, and I wanted to design a simple 'sensor shield' --since all simple sensors has 3 pins (namely, SIG-5V-GND) and it is convenient to connect bunch of them directly-- and ...
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2answers
176 views

What formulas do I need to use to design a voltage regulator circuit for a zigbee radio?

I've written the code for my zigbee radios, but now I face the obstacle of getting them onto a carrier board to allow access to VCC, GND, TX, RX via a 4 wire connector. The supply voltage is 3.712 ...
3
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4answers
413 views

Decoupling capacitor across Raspberry Pi GPIO input (+ Arduino + robotics)

I've been messing around with a robot kit from Parallax (the BOE Shield Kit), which has a 5xAA (7.2V?) power source. The BOE Shield includes its own 5V regulator, which is used to control servos that ...
7
votes
1answer
418 views

Best place to place a decoupling capacitor

See this image which gives four options to place decoupling capacitors: (from http://www.learnemc.com/tutorials/Decoupling/decoupling01.html) I would say option (d) isn't good - I would recommend ...
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5answers
2k views

What's the use of a decoupling capacitor near a reservoir capacitor?

I've seen some circuits where a decoupling capacitor is used as well as a reservoir capacitor, like this (C4 and C5): I've read about decoupling capacitors and for me it looks as if they are meant ...
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3answers
244 views

Which connection(s) to a decoupling capacitor should be shortest?

Circuit Cellar-Issue 210- has this question "Which connection(s) to a decoupling capacitor should be shortest?why?" in its "Test your EQ section". I couldn't understand what they meant 'Which ...
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3answers
225 views

how many caps required for 3.3V rail for 500ma?

How much capacitance do I need on 3.3V rail with loading of ~500mA? I have 22uF caps that I can use. In general, what is a good rule of thumb on how much capacitance required based on a voltage rail ...
5
votes
2answers
285 views

How do I decople a microcontroller with odd number of ground pins?

I'm building a DIP adapter board for MSP430FR5739 and I want to include the decoupling capacitors on the adapter board itself. From what I can see, I'll need a capacitor on the analogue and digital ...
7
votes
1answer
446 views

Is my design good enough in terms of noise and EMI as its 80MHz MCU board [closed]

Recently I'm trying to design a PCB board for an MCU. The problem is I haven't considered any noise aspects before. As I'm in a contest for new electronics product run by our university I have to ...
2
votes
1answer
848 views

What's the use of the bypass capacitor on the LM380 amplifier?

I've read the LM380 amplifier data sheet and application notes, and they show a power supply ripple rejection number that's based on the size of the bypass capacitor. There are also a few designs that ...
21
votes
3answers
9k views

Can I replace all electrolytic capacitors with ceramic ones?

I am designing the power supply circuit for a system that needs several supplies, my questions are: Is it possible to replace all electrolytic caps (Mostly 100uF) by ceramic ones? What are the ...
4
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1answer
575 views

Inductive choke with bypass capacitors?

I've been looking at a few power input circuits and quite a few of them suggest an inductive choke with a large bypass capacitor followed by smaller bypass capacitors. In theory this is what I ...
5
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4answers
2k views

USB powered device with multiple Decoupling Capacitors

I have a USB powered device with multiple IC's. From what I've read it's standard practice to use a combination of multiple range capacitors for decoupling each individual IC, with the smallest being ...
2
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3answers
347 views

Placement of decoupling capacitors

The recommended power schematics for Atmel's AT32UC3C (figure 6-1) shows the use of 2 decoupling capacitors from the power supply to the digital circuitry, CIN1 and CIN2. These are meant to decouple ...
4
votes
3answers
1k views

How much capacitance do I need in the input of LM78L05

I want to use LM78L05 as a fixed output voltage regulator as shown in the datasheet, as I cited below. My regulator is 2 meters away from the power supply filter. My input voltage is 24V, however this ...
3
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2answers
740 views

Capacitor selection with multiple regulators

I'm working on a circuit that needs three voltage regulators: +24VDC, +12VDC, and +5VDC. The power input is +28VDC from a bench power supply. The +24VDC regulator is a 78M24. It is supplied from ...
3
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1answer
975 views

Are small valued capacitors effective in the device power input?

I am really confused with all of the ground bounce, decoupling, bypassing, filtering, resonance and ESR&ESL stuff. What I currently understand is: Ground bounce occurs when the (capacitive ...
5
votes
4answers
871 views

How important is it to put decoupling caps on the same side of the PCB?

How important is it to have decoupling capacitors on the same side of the PCB as the IC? I am desperately short of space in a design, and it would really help to put the caps on the bottom side. I ...
5
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2answers
266 views

Adequate decoupling / noise reduction for two accelerometers?

This is my first PCB, so please forgive some of my ignorance! I'd like to mount two accelerometers (ADXL193: +/- 250g), orthogonally, on the same PCB, and have a question about noise. The current ...
4
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3answers
254 views

Combining capacitors for multiple chips

I'm building a circuit that uses multiple chips. All of them require a capacitor to be connected in parallel to the VCC line (as seen in the datasheets). Since capacitors are used to reduce voltage ...
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2answers
530 views

TLC5940 and ADXL335 circuit 'glitches' on perfboard. Need decoupling caps?

I created a circuit containing one TLC5940 and one ADXL335 breakout board. The ADXL board comes configured with 0.1 uF capacitors to set the bandwidth of each axis to 50Hz. It is wired to an Arduino ...
3
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1answer
2k views

Why do we need 100nF cap in the output of an SMPS?

I was looking at Micrel AN-53 and I have noticed that in a circuit in the first page (circuit is below), at the output of an 400KHz, 27V, 7A, 180W boost converter, there are two 680 uF, two 10 uF and ...