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41 votes
Accepted

I ripped the lead off this film capacitor by mistake - is it beyond repair?

Do not try to repair the capacitor. You're more likely to create a short and possibly damage something else in the circuit. Just buy a suitable replacement. The leads are connected with the edge of ...
Spehro Pefhany's user avatar
24 votes
Accepted

Why does this isolation transformer have another transformer in it?

That "transformer" is a common mode choke. It's used to suppress EMI (either being induced onto the line and affecting the circuit or being transmitted from the circuit out over the line). It's ...
Curd's user avatar
  • 16.3k
21 votes
Accepted

What is this white trace on this PCB?

It's a visual indication of where the separation is. It makes it easy to visually inspect that there's 8 mm creepage distance with no components or tracks in the 'keep out' zone. That's the charitable ...
Neil_UK's user avatar
  • 167k
20 votes
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Safest way to ground a metal enclosure

Option 4: bond the enclosure to earth, and connect it to the clock ground with a high impedance, maybe 1 megohm. This prevents large voltages building up between the internal circuit and the enclosure,...
The Photon's user avatar
  • 130k
16 votes

I ripped the lead off this film capacitor by mistake - is it beyond repair?

It really is not worth trying to attach the leg back to capacitor. The layers may have suffered mechanical damage. Buy a new one.
Justme's user avatar
  • 151k
15 votes
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Protecting two layers of PCB with electric tape?

Kapton tape is a widely available industry standard product for this scenario. You can view the specs here - from table 3 you can see that it has a dielectric strength of over 100kV/mm, plenty strong ...
BenAdamson's user avatar
15 votes
Accepted

Why are there so few oscilloscopes with dedicated isolated channels?

Why are there so few bench osilloscopes with dedicated isolated channels? Is it a design issue, a cost issue, a business issue or is it just better with differential probes? It is a cost (price) ...
Bimpelrekkie's user avatar
13 votes
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Relevance of Galvanic Isolation of Boost Converters

Galvanic isolation means that no (significant) current can flow between two parts of the circuit (here, the input side and the output side). It doesn't mean the output voltage of a circuit has to be ...
marcelm's user avatar
  • 2,597
13 votes

Preventing oscilloscope magic smoke by inverter vs isolation transformer? Good idea or not?

The problem is you touch your oscilloscope a lot when you're working with it. Things like buttons and knobs with metal and circuitry right behind them and are not designed to isolate high voltages; ...
DKNguyen's user avatar
  • 56.8k
13 votes

Why is the telecom input power supply range 36 to 72 V (polarity ignored)?

It's to allow a telephone exchange to run on batteries during a power cut. Specifically, a 48V stack of lead acid batteries. While the batteries are charging, the voltage could be around 57V. When ...
Simon B's user avatar
  • 19.4k
11 votes
Accepted

How is galvanic isolation established in an SMPS?

Sure they have transformers: - The transformer looks different to a regular AC type but it's still the largest single component on the PCB but a whole lot smaller than it would be for 50/60 Hz ...
Andy aka's user avatar
  • 460k
11 votes
Accepted

Does power delivery over ethernet always have to use isolated DC/DC converters?

If you want to call it PoE, you need to stick to IEEE 802.3af-2003 or IEEE 802.3at-2009. These standards call for isolation. This answer could end here: no, you cannot build a PoE device without ...
Marcus Müller's user avatar
11 votes

Can an op-amp's Vin+ and Vin- be outside the supply voltage as long as their difference is inside it?

Generally speaking, no. The datasheet should clearly tell you what is permissible without damage and what might work and what is guaranteed to work (six different numbers in general). Both inputs of ...
Spehro Pefhany's user avatar
11 votes
Accepted

Puzzle how isolated RS-485 (ADM2582) sends signal without signal ground

It works due to RS-485 receiver having a high but yet finite input impedance which equalizes common mode potential between the two chips even without the common reference wire. And this is also the ...
Justme's user avatar
  • 151k
10 votes
Accepted

Can I use a dual primary transformer to generate isolated 110v output?

You can if you only need functional isolation. If safety isolation is required you need a transformer designed for that. Since you are only powering half the primary you can only put in half of the ...
Jasen  Слава Україні's user avatar
10 votes
Accepted

Why does increasing altitude (low air pressure) results in lower resistivity/ breakdown voltage?

The behaviour is described by Paschen's Law. Electrons are accelerated in the electric field between two electrodes. If there are gas molecules in the path of the electron it will collide with them ...
jusaca's user avatar
  • 9,609
10 votes

Is this a safe way to measure mains power on an oscilloscope?

From your description, it sounds like you've made a safe isolated source of 9 VAC. To verify that the output is isolated from the AC Mains, you could measure (with the thing unplugged!) the resistance ...
Peter Bennett's user avatar
10 votes

What is this white trace on this PCB?

Look to the PCB very carefully. The white area is made with the same silkscreen legend print as used for part numbers and part outlines. It is a paint cured by UV light or heat in order to be ...
Uwe's user avatar
  • 2,812
10 votes

What options exist for isolating a high power DC analog signal?

Analog Devices has a large portfolio of isolated amplifiers and data converters. Many of them include isolated power, so you don't have to come up with a low voltage power source on the field (high ...
AnalogKid's user avatar
  • 20.6k
10 votes

Puzzle how isolated RS-485 (ADM2582) sends signal without signal ground

The RS485 standard says transceiver and receiver grounds should be connected. This gives much better noise immunity and is how it should be done, but... some equipment doesn't have the ground ...
bobflux's user avatar
  • 78.2k
9 votes
Accepted

Efficient method for isolated detection of AC voltage without a stepdown transformer

Here is how I have dealt with AC line detection in an efficient manner using an isolated opto-coupler. Key attributes of the circuit: The selected opto-coupler is one with a low forward current ...
Michael Karas's user avatar
9 votes

Why does this isolation transformer have another transformer in it?

That is what's known as a common-mode choke. It presents a high impedance to any common-mode currents which might flow in the + and - pairs. Any common-mode currents which flow in the attached ...
ConduitForSale's user avatar
9 votes

RS 485 ground signal and chassis

Looks like a common mode voltage problem to me. Although differential signalling, it still needs a common GND. (source) Replace your 1nf 500v capacitor with a jumper. Or wire signal ground to all ...
Jeroen3's user avatar
  • 23k
9 votes
Accepted

Isolated audio without a transformer

Is there any reason this wouldn't work the way I think it would? You cannot expect that circuit to work because the guitar signal ground connection has to connect into the op-amp circuit ground node ...
Andy aka's user avatar
  • 460k
8 votes
Accepted

How can a higher power circuit share the ground with a lower powered circuit?

Because of a basic rule of electricity, current only flows around circuit loops. When you have two circuits, with no other connection between them, you can tie them together at ANY point to form a ...
Trevor_G's user avatar
  • 46.7k
8 votes
Accepted

How do they get good primary-secondary isolation on concentric windings?

There are two keys to making such a concentrically wound design work safely at mains voltage: For most insulating materials used for the interwinding film, mylar included, DTI (distance through ...
ThreePhaseEel's user avatar
8 votes

Spikes in raw acceleration data from AC motor

The spikes seem to have a few common heights that are roughly related by factors of 2, which strongly suggests that they are noise-induced single-bit errors in the binary data. One good way to ...
Dave Tweed's user avatar
  • 173k
8 votes

Optocoupler with the same power supply

No, there is no good reason to use an expensive and large optocoupler if you're sharing ground. The optocoupler's prime advantage is isolation. The common use of this appears to be cargo cult adoption ...
awjlogan's user avatar
  • 7,939
8 votes

Safest way to ground a metal enclosure

From a safety standpoint the enclosure should be connected to earth, not to the neutral leg of the power supply. You should have a three prong plug with the enclosure connected to the ground pin. ...
Ross Millikan's user avatar

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