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. EMC depends upon many system-level details; when asking questions, please provide as much information as possible.
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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 ...
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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 ...
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Spikes induced on PCB. EMC problem?
I designed the following PCB, where after testing a faced a severe (EMC related?) problem.
This board houses an STM32F103 developing board.
On the right of the PCB, there are 6 thermistors connected ...
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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.
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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 (...
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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,...
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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://...
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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 ...
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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 ...
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Conducted EMI of buck converter is too low even without filter
I have simulated a 48 V to 12 V buck converter with LISN in LTspice. However, CM and DM EMI is way below CISPR limits. I want to simulate a real world converter. How can EMI be increased?
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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 ...
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GSM noise from a 2-layer PCB with SIM800C
I've designed a 2-layer PCB that contains a 12-5V buck converter (P2576L-50 - a Clone of the LM2576), 3.3 (AP1117-33) and 4V (MIC29302WU) shunt regulators, an STM32 micro and a SIM800C GSM module.
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NPIC6C596 resets itself
This is a board with an ESP32, 16 relays, and other IO.
I'm using two power shift registers NPIC6C596 to drive the relays...
...and here's one relay.
NPIC6C596 normally runs on 5V, I used 3V3 by ...
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Equivalent circuit of CM and DM EMI filter
This is the diagram of an EMI filter consisting of both CM and DM filters:
This is the equivalent circuit of the CM filter:
Could someone explain why in the equivalent circuit, it's Lcm and not 2Lcm?...
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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 ...
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Is twisting a single ended signal with its own GND really useful?
I know that the most robust way of transferring an analog signal over long distances is via differential pairs which are twisted together and then shielded (shield grounded at one end only).
But ...
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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 ...
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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 ...
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Why do some PCBs have exposed plated perimeters?
I've seen a number of PCBs, largely high speed and RF boards, that have exposed copper, either at the perimeter of the entire board, or in various sections, often with stitching vias.
I've never ...
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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 ...
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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 ...
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Why exactly is it discouraged to gap the ground plane?
From time to time I hear (and read) that it is not good to make separate Gnd planes for digital and analog circuit parts. It's all summarized in this rule of thumb: "Don't split the Gnd plane, don't ...
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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 ...
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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 ...
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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 ...
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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 ...
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How serial resistors actually reduce EMI?
I am recently working with a GSM based system, and there was this advice in the datasheet of the GSM module:
22 Ω resistors should be connected in series between the module and
the SIM card ...
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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 ...
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4 layers PCB stack - (signal, signal, power, ground)
I've developed a board for a project and the company that is going to assemble it in a pluggable module has just asked me a weird modification.
Currently it's a 4 layer board: top signal, ground, ...
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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 ...
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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 ...
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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 ...
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Radiated emissions from WS2812 LEDs
We have a product which is failing EMC testing on radiated emissions. It fails by approx. 25 dBuV at the peaks. The product has a large 550x900 mm opaque 5mm acrylic window. Behind this, at a 50 mm ...
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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'...
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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 ...
user98663
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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/...
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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 ...
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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 ...
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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 ...
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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.
...
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Quasi-peak detector
This is the circuit of a quasi-peak detector:
simulate this circuit – Schematic created using CircuitLab
where \$ V_{\text{sig}}\$ is the input signal.
When the diode is open-circuited, the ...
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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 ...
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How to simulate the impedance for this LISN circuit in LTspice?
I tried to simulate the following simplistic LISN circuit:
Below is the AC analysis with LTspice for two nodes:
But these above plots do not tell me anything related to the purpose of LISN which is ...
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Understanding topology for EMI supression in a power supply
I am using an isolated DC/DC converter to supply a MOSFET's gate drive, in a high frequency and high voltage application, so I am concerned about the EMI in my design.
In the website of the ...
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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 ...
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EMI suppression low frequency
I'm dealing with a PWM generator which drives a load at 12V with pretty high currents (5-10A)
The PWM frequency is in the band of 100-200 Hz. Which is the best choice and right configuration of ...
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EMI Input Filter Design
I have been reading and watching TI's material on EMI input filter design, and I have a few questions.
My basic question is "How do you select the component values for your EMI input filter?"...
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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 ...
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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. ...
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How does this modulation cause sidebands?
The following figure is an excerpt from this paper: Input Differential-Mode EMI of CRM BoostPFC Converter by Fei Yang.
Q#1 (first highlighted sentence): How does the modulation line frequency cause ...
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