Questions tagged [emc]

Electromagnetic compatibility (EMC) is a branch of electronics related to identifying and solving problems caused by electromagnetic interference (EMI) between devices. It encompasses both attempting to prevent unwanted emissions from a device and also ensuring that emissions from another device will not cause spurious operation.

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55
votes
3answers
29k views

What does the Y capacitor in a SMPS do?

It seems that a well-designed SMPS has a capacitor connecting the ground planes of the primary and secondary sides of the transformer, such as the C13 capacitor here. What is the purpose of this ...
21
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2answers
9k views

Via fences for noise reduction of a chip antenna?

I'm working on a 4-layer PCB that has a wifi module and a chip antenna, the antenna is placed at the corner of the PCB and the copper beneath it is removed, I see that via fences are used on the ...
27
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4answers
7k views

Why is it good to slow down digital lines with resistors?

I've heard that sometimes it is recommended to "slow down" a digital line by putting a resistor on it, let's say a 100 ohm resistor between the output of one chip and the input of another chip (...
18
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3answers
7k views

What problems could occur when chaining 40 shift registers?

I'm planning on chaining together 40 x 74HC595 shift registers. The whole chain of 74HC595s will be controlled by a 5 V microcontroller, which will generate the SDI,...
8
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1answer
3k views

EMI/ESD protection for USB interface?

I'm a student making a simple Arduino-compatible board similar to the Pro Micro and am going to put a USB connector on the board. The schematic in the above link doesn't show any kind of EMI/ESD ...
12
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1answer
4k views

How can electromagnetic interference from a USB charger cause a capacitive touchscreen to malfunction?

Electromagnetic interference from a USB charger can cause a touchscreen on a mobile device to malfunction, with symptoms such as reduced sensitivity or spurious touches. As an example, see http://...
4
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1answer
1k views

Dealing with splits in my ground plane

Whenever I'm making a cheap, 2-sided PCB, I run into this problem: Where I have signal lines (on the top layer here) running over top of a big fat power trace (on the bottom layer). Now, this is ...
1
vote
1answer
2k views

emi standards/best practices for PC cases

According to an EE friend, the FCC specifies EMI tolerances (max outputs) for PC components, including cases. However, here it says that there are standards for a number of components but not cases. ...
40
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3answers
4k views

What's radiating on my PCB?

I recently did a proper EMC test on a PCB of mine. It failed the test, and seems to be radiating in the 300MHz - 1GHz region, with peaks every 50MHz, and little peaks on the 25MHz. Looking at the ...
24
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2answers
3k views

Alternatives to SPI because of EMI

I currently make a system consisting of a plastic enclosure which contains an MCU talking to 7 ADCs using 2MHz SPI over wires about 5cm long. The problem is that I'm concerned about EMI. Everything ...
18
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2answers
4k views

PCB routing: EMI and signal integrity, return current questions

If there's any EMI/SI lesson I've taken in, it's to minimize return loops as much as possible. You can work lots of EMI/SI guidelines from that one simple statement. However, not having or ever even ...
12
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1answer
4k views

PCB 'Emi proof' design

Currently I'm designing a GPS basestation which will have a radiomodem (broadcasting at 407-480MHz), a ARM7 microcontroller running at 60MHz and a FTDI USB chip. The FTDI USB chip even runs at 480MHz ...
16
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2answers
3k views

Why are caps configured this way in EMC filters?

Every EMC filter I've seen has capacitors between the AC lines and earth, configured like this: simulate this circuit – Schematic created using CircuitLab Why are the caps not configured like ...
7
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4answers
5k views

What is the purpose of holes on edge of the PCB?

Here is a photo of one of Texas Instrument's RF EVMs. Please pay attention to edge of the PCB that has multiple tiny holes. I marked 3 of them with a red circle on the photo. What is the purpose/...
7
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2answers
8k views

What is the best way to layout a PCB with crystal oscillators and MCU?

I have heard that the clock circuit is a noise source and that the clock circuit is also sensitive to noise. I believe that keeping the clock circuit close to the MCU and keeping other routes or ...
6
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3answers
987 views

What is the thought process for specifying an EMI bypass cap on line transformer secondary?

Update It turns out I had mistakenly interpreted the role of the capacitor in question here as an EMI filter for line noise. It looks like a capacitor in that position actually serves as a snubber ...
5
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2answers
1k views

How do I cycle a WiFi transmitter through all modes, for FCC intentional radiator EMC testing?

I'm integrating a WiFi/Bluetooth module into a consumer product, however the module does not have a modular grant, will not have a modular grant, and is anyway getting paired with a unique internal ...
36
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4answers
1k views

Identifying Source of Periodic Artifact at Op-Amp Output

My MAX44251 dual op-amp has a very small unwanted 131KHz periodic artifact at the output, seemingly regardless of how it's configured. My assumption was EMI, but I can't see this 131KHz signal on any ...
11
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10answers
6k views

EMI: CFLs vs Incandescent Lights in Your Lab?

Being a green-oriented treehugger, I've put in all CFL lights in my house. Just as much light for about 1/4 or 1/3 the power. Nice, but flourescent lights put out a lot of EMI. Does this cause ...
10
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1answer
3k views

What certification is needed for electronic devices in Europe?

I am going to be selling my project, Super OSD. It has a 3 MHz SMPS PSU and an 8 MHz crystal oscillator, but is not intended to emit radio signals. Will it be necessary to get testing to sell in ...
4
votes
4answers
4k views

Ground plane directly underneath physically large 100 µH inductor?

I plan to use a physically large ferrite core inductor (Murata part "1410478C", 100 µH at 1 kHz) in a 12 V, 7 A DC filter circuit. It will be mounted on topside of a four-layer PCB ...
2
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1answer
136 views

Reducing EMC from a long trace where one end is normally floating

Following on from this question about a PCB layout with EMC issues, I'm currently reworking the design to minimise breaks in the ground plane and try and identify any other EMC issues. One thing that ...
2
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1answer
1k views

LC Filter for Phase Control

Can you point me to a good online resource to learn how to understand and design LC filters? The goal is digital forward phase control to dim a light bulb. I've read that the EMI produced by the ...
9
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1answer
629 views

Optimize signal return path with decoupling capacitors in a two layer board

I'm designing a pretty complex two layer board - I should really go for a 4 layer one, but that's not the point here. I'm done with component placing and routing and I'm doing the finishing touches ...
8
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1answer
2k views

When is it appropriate to use ferrite beads?

In a lot of circuits, I've seen ferrite beads on the Vdd lines to microcontrollers. For my high speed dsPIC33F (80 MHz, 40 MIPS) microcontroller, should I have ferrite beads on the Vdd lines or should ...
7
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2answers
670 views

EMC testing of unenclosed PCB assembly

What is the most common practice in performing EMC tests for PCB assemblies that will be sold without a housing? In my case it is an FPGA development board. Is it possible to design excessive ...
7
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1answer
295 views

High Frequency Characteristics of Solder-Filled Vias

If a via gets plugged with solder, does this destroy its ability to pass high frequency (RF noise) currents? Since there is no longer a surface along which the high frequency currents can travel due ...
4
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2answers
1k views

Where to connect shield and ferrites in PCB with isolated planes

I have a device which has two sections of the PCB completely isolated form each other, but connected by an isolator IC (PN: ????). I think I need to shield the whole device for reducing EMI because ...
3
votes
1answer
2k views

Why put capacitor between ground and chassis?

In the product I analyse (an optical fork sensor, rated 10V-35V), there is a sizewise big capacitor between ground and chassis. I measured its value with an LCR meter, it is 60nF. I also broke one by ...
2
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1answer
1k views

Transient protection to prevent microcontroller freeze - Selecting MOVs and TVS diodes

I have a circuit which contains an offline switching SMPS circuit (based on viper22a) converting 220V to 5V regulated down to 3.3V using linear regulator IC. This powers up an ESP wifi module and ...
11
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1answer
1k views

Weak internal pullups on microcontrollers and EMI susceptibility

What disadvantages can I run into when using weak internal pullups (100k) on microcontrollers? I'm wondering how susceptible lines (with only parasitic trace/component capacitance) become to EMI ...
11
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2answers
1k views

EMI Issue: Ringing in switch mode power supply layout (5V -> 3V3)

I am working on a device which is undergoing testing to pass FCC part B (CSRR 22) emissions. At one angle and polarization (Vertical) the device fails as it has emissions in the 100-200Mhz range which ...
7
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4answers
2k views

How to fix EMC problems for existing designs?

I'm going to be looking at a few products that have failed EMC radiated emissions testing and will need to apply fixes in order to make them pass (unfortunately, in these cases, two of the designs can'...
4
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4answers
3k views

Why is a caseless PC not an EMI problem?

As I understand it, the case of a PC is metal so that it can form an EMI enclosure around the electronic parts. My view is reinforced by there being conductive fingerstrips around the mating edges. ...
4
votes
3answers
918 views

At what point does the responsibility of the manufacturer end with regards to FCC/CE testing?

I'm curious as to when the responsibility of a manufacturer ends when dealing with emissions and RF testing, part of FCC and CE tests. I repair TVs as a hobby and as business. I got a TV in from ...
3
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3answers
1k views

safe to use an unshielded jack for 10Mbps Ethernet?

I have a hardware device which includes Ethernet connectivity. I have a surface-mount Ethernet jack, with top entry (as opposed to right-angle). Part number is RIA Connect AJS03B8813, if that helps. ...
3
votes
1answer
168 views

Analogue (or digital) signal integrity with multiple sources of noise

tldr: Can I transmit an analog signal through a noisy environment without it being corrupted, or should I use a digital signal instead? My requirement is to transmit a signal from a MA3 absolute ...
3
votes
2answers
15k views

How is quasi peak calculated

As said in the headline, how is quasi-peak calculated? I was not lucky on google this time, so I will ask here. I'm just looking for the formulas behind the calculation, since I want to make some ...
2
votes
1answer
350 views

Current rise time. How fast is too fast?

I'm trying to create a suitable response to Pumping a few Amps for a 100usec. The OP wants to create a 5A current pulse for 100us. They want to have a current rise time of 1us at the start of the ...
2
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3answers
779 views

Connect signal ground to safety ground?

We are designing a product which has to meet EMC directives. It consists of metal backplate folded into a chasis (the front is open). on the backcover there is a SMPS mounted. and on top of this we ...
2
votes
1answer
630 views

Square Wave pulses generating EMI

Following on my unanswered question about bluetooth noise, I have now believe that I have learned a bit more about my problem. I have built a Arduino controlled circuit to replace the pots and ...
2
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1answer
3k views

Resistance and Inductance of a ceiling fan motor needed to spec snubber

I'm looking to specify (well, suggest) a RC snubber network for someone over on diy.se who is having EMI problems with his ceiling fan knocking out his TV briefly on turn-off: https://diy....
2
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2answers
1k views

Switching power supply using faraday cage and EMI protection?

Several switching power supplies in the market use this kind of cages to protect the circuit, however, i have this question, A) Is this used as a faraday cage due to the high frequency used by it? ...
1
vote
1answer
264 views

Alternative Gigabit Ethernet Connector - considerations for impedance, signal integrity, and EMC considerations?

I have a design that does not have enough vertical clearance for a standard RJ45 socket. I'm hoping to use a connector like this one from Molex. I will use Cat5e cable when building my cable with the ...
1
vote
2answers
2k views

PWM controller to meet EMI/EMC regulations

I'm designing an application in which the current running into a load is controlled by PWM. A microcontroller generates a PWM cycle at 20kHz and this signal is used to control a MOSFET which is ...
0
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1answer
435 views

Protecting Electronics From RFI and EMI

Part 1: the system and how it's connected I'm working on a system that would monitor the water level of a water well in remote areas . Here's what the system is designed ( drawn briefly ) , On the ...
0
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1answer
171 views

Are LCD/Plasma/Smartphone monitors susceptible to EMR eavesdropping?

Having just read about EMRTempest eavesdropping; I find myself wondering whether EMR eavesdropping is defeated by FCC regulations on interference With the advance of technology from CRT to the newer ...
0
votes
2answers
88 views

Is my simple atmega2560 based product exempt from EMC testing?

I have designed a product that is essentially a USB HID device for a computer game. It consists of several on off switches and 5v servos run by an atmega2560, all sealed and enclosed in a plastic case....
0
votes
2answers
532 views

Improve signal integrity of Ethernet signals (if indeed is needed)

Actually it is nothing to do with Ethernet specific, but just to be accurate, I have several SS-SMII Interface signals between an FPGA and a Switch. The interface has 8 data signals, one ...
0
votes
2answers
401 views

Wire length, EMI and comms failures

I am designing a system which has a lot of wires. These pass power, communications (RS422), ethernet and even analogue video (NTSC,PAL). Now, these wires meander all over the place. One of the wires ...