Allowing for the flow of power or information without shared electrical nodes

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25
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4answers
5k views

Why are the high voltage overhead power lines with the same potential being isolated?

Photo #1 Photo #2 Photo #3 - A zoom of Photo #1 Photo #4 - A zoom of Photo #2 I shot these photos while travelling in a highway. In each line-group has three separate lines. I think that the ...
18
votes
4answers
5k views

Why is it important for mains power supplies to be isolated?

In all the computer power supplies and other power supplies I've taken apart, I've noticed they are fully isolated from the mains. Galvanic isolation through transformers, and often optical isolation ...
12
votes
3answers
4k views

Cellphone charger has no transformer?

I opened up a really tiny mobile phone charger I have, to see how it is designed. The entire "charger" is integrated into a small 2-pin mains plug, 1 x 1.25 x 0.5 inch, that has an USB socket for the ...
11
votes
2answers
1k views

Why AC points on PCB are separated by a hole

I want to find out why, in professional PCB's, they separate between the AC (220 VAC) points on the PCB with a hole in the PCB: Is it for more isolation between the AC lines? Is leaving a distance ...
11
votes
2answers
6k views

What values of resistor and capacitor to use for AVR reset pin isolation?

Background... I'm a newbie to AVR applications. I recently built two ATTINY13-based circuits (glorified LED blinkers) which worked correctly (independently) on the breadboard. When I combined them on ...
9
votes
1answer
1k views

Why does TO-220 79xx voltage regulators conduct the input voltage to the heat sink?

I find it somewhat dangerous to connect a large heat sink on 79xx series voltage regulators. Because they transfer all the negative voltage to the heat sink. Why just they didn't make the 2nd pin of ...
8
votes
3answers
839 views

Are there any disadvantages using magnetic couplers instead of opto-couplers?

I'm trying to find the disadvantages of using magnetic couplers versus opto couplers (1). I'm deciding which of the two I should use to create a galvanic isolation between two PCB's that are going to ...
8
votes
4answers
1k views

Sensing DC motor current

I am allowing the current through a DC motor to flow through a small resistor and measuring the voltage across it. I need to give this analog Voltage to an ADC of micro-controller to do some signal ...
8
votes
2answers
206 views

If I put multiple isolated DC/DC converters in series, can I add their isolation voltages?

Suppose I have a DC/DC converter that's rated for 2250VDC isolation for one minute. If I put two of these devices in series, making sure to maintain proper clearances on my PCB, do I get an effective ...
7
votes
2answers
377 views

Isolation transformer to reduce speaker pop

I have some computer speakers which suffer from the following problem: when switches flip in certain devices in the house, like the thermostat on a radiator or the refrigerator, the speakers will emit ...
6
votes
4answers
2k views

how to electrically isolate a PCB from a heat sink

I have a set of LED driving lights on my motorcycle that must be wired through a ground-leg pulse width modulation dimmer. The problem is the mounting bracket for the lights is grounded, so the lamp ...
6
votes
2answers
1k views

Isolation Transformer

When a function generator is used to power a full wave rectifier an oscilloscope will not show the correct output due to a shared ground. A half wave is displayed because one of the diodes is ...
5
votes
3answers
190 views

Digital Isolation comparison

I am currently using ADuM4160 by Analog Devices as a USB isolator. However, this part is EXPENSIVE. I was wondering if anyone thinks it can be replaced with ADuM2200. Any reason why this wouldn't ...
5
votes
2answers
1k views

Isolation transformer and scope when troubleshooting SMPS

I have a simple question, when troubleshooting a SMPS is highly adviced to use an Isolation transformer. But my question is this, if im using a scope to troubleshoot the "hot" side of my SMPS, both ...
5
votes
3answers
1k views

Why is power supply from electrical utility referenced to earth?

In response to the question Basic Training for working with 120V AC zebonaut had replied that "A regular wall outlet is referenced to earth" and this provides the close loop for the circuit to ...
5
votes
3answers
1k views

Cutting the ground wire in an isolation transformer?

I bought a non-tech isolation transformer (500w), which I planned to cut the earth mains ground from the output, but leave the chassis grounded; however, when I opened it up I found the output outlets ...
5
votes
1answer
310 views

How is pouring water addressed in high-voltage electric transport systems?

An electric train is typically powered with something like 1.5 kilovolts of direct current of something like 25 kilovolts of alternating current. In my experience electric device manufacturers charge ...
5
votes
1answer
443 views

Determining if a power supply is isolated?

I've been looking for a low cost adapter I can use to power some electronic circuits I'm playing with. Pretty much the only requirement I have at this time is that the adapter is mains isolated for my ...
5
votes
1answer
4k views

Is galvanic isolation of Hi-speed USB impossible?

I have a USB isolator which provides galvanic isolation of a USB device from my PC, but only works for low speed and full speed USB. I can't find any alternative electric isolators which do provide ...
5
votes
1answer
282 views

Isolation for microcontroller that is off

I have a design where power savings is a huge issue and even the lowest power sleep mode of the \$\mu\$C is too much quiescent current (30 \$\mu\$A). I'm aware of many and have used \$\mu\$Cs in the ...
5
votes
1answer
778 views

How should I isolate AC and DC on a small PCB?

I am designing a small PCB (1"x1") and it will have some DC logic traces (5V and GND) and some high frequency AC power traces (100V 1000Hz 50mA). Are there any special considerations I need to take ...
4
votes
1answer
754 views

Best way to measure 230VAC

I'm trying to design a circuit to measure power of 230VAC (MAINS), with the ADC of a small MCU. I have designed the part of the circuit to measure current, but my solution to measure voltage is ...
4
votes
3answers
416 views

Why are the pins on the official arduino motor shield so long?

Here is the Official Motor sheild website. The shield has pin connectors at the bottom that are 2x longer than on any other shield I've seen. Why is that?
4
votes
2answers
533 views

DC/DC isolated supplies in series for higher voltage?

Can I chain two isolated DC/DC supplies together for a higher output voltage? (Say, a 48V and a 12V to get 60V?) They'd be fed from the same 24V DC source. I've asked a related question before ...
4
votes
1answer
155 views

how to test isolation of DCDC convertor?

I have an isolated DC-DC convertor which boasts a 1.5kV isolation. I have a PCB made along with the additional components it requires. How can I test it?
4
votes
1answer
102 views

Do I need to isolate the output voltage feedback in SMPS?

I almost finish with my Half-Bridge SMPS design. I'm now designing the output voltage feedback to the controller stage. The controller stage drives both MOSFET transistor through an isolation ...
4
votes
3answers
1k views

home brew isolated oscilloscope lead

The ground clip for an oscilloscope lead is normally connected within the instrument to the power supply earth, and there are surprising circumstances where this could matter. The situation is very ...
4
votes
2answers
253 views

When is it appropriate to galvanically isolate components/subsytems?

As the question implies, how do you determine when it is appropriate to galvanically isolate parts of the same electrical system from one another? For example, I'm currently constructing a tube ...
4
votes
2answers
401 views

Electrical Isolation

I've been reading about the EIA-485 standard and they talk about how even with twisted pair wire they need a 3rd connection for common because sometimes the devices need to be isolated. I was thinking ...
4
votes
1answer
75 views

ADuM1301 digital isolator - PCB layout question

We are using the ADuM1301 digital isolator in one of our designs. The PCB layout section from the data sheet states: In applications involving high common-mode transients, care should be ...
4
votes
2answers
337 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 ...
4
votes
1answer
262 views

How do AC and DC hipot tests compare?

Suppose I have a DC/DC converter, Recom RPP30 for an example to hand. It lists an isolation voltage of 3000 VDC. How does this translate to an AC isolation voltage? Would this be equivalent to 3000 ...
3
votes
3answers
334 views

Isolation of watch crystal from ICSP

I'm working on a project which uses a PIC with a 32kHz watch crystal attached to Timer1. Unfortunately, the chip I'm currently using, PIC16F1827, shares the T1OSI & T1OSO pins with ICSPCLK & ...
3
votes
3answers
332 views

Sensing signal on a power line from high side

I have a circuit design as above. I'm trying to sense the voltage difference accross the \$ 0.1 \Omega \$ resistor. I physically connected the sensory circuit to the low side of the AC line, and saw ...
3
votes
3answers
356 views

Mains triac safety circuit design

I am investigating using a triac instead of a relay to control 250V 10A devices. However all the 600V 16A triacs come in TO-220 packages. According to AS/NZS 3100 and AS/NZS 60335.1 I need at least ...
3
votes
2answers
313 views

How to properly isolate multiple power supplies

Say you have a single 110V AC supply and need to use it for a number of devices, each requiring very different characterists. For me personally these are: a direct use of the 110V AC supply for a ...
3
votes
2answers
425 views

Why DisplayPort cables must isolate the power pin?

I've been investigating why my 2560×1440 DisplayPort monitor and my mini-DisplayPort MacBook Air don't play along, and, it turns out, this is likely due to a wire in the cable that connects the two ...
3
votes
3answers
200 views

What is the electrical connection of heatsink plate of PB case bridge rectifier packages?

I'm going to use two PB-case bridge rectifiers of a certain product in my circuit. I need to know the electrical connection of its heat-sink plate (i.e.; to what pin it is connected to, or if it is ...
3
votes
1answer
157 views

Proper power design for a USB device

I'm designing a USB device that I want to be powered eintirely from a wall wart and have a couple questions concerning the power connections and ground loops. 1) If I connect the USB GND pin to ...
3
votes
4answers
601 views

Measuring voltage while maintaining isolation

I'm building a variable power supply, and want to provide the ability to digitally measure the outputted voltage and current. The digital power supply used to drive the ADC, microcontroller and ...
3
votes
1answer
124 views

AC leaks to laptop, cellphone surface. Feel by finger! [closed]

I've accidentaly discovered that several mains+battery-powered devices with metallic casing like cellphones, laptops and mp3 players, exhibit a special kind of friction when stroked with a finger. But ...
3
votes
1answer
194 views

Are the non-metallic colored heat sinks of transistor packages electrically isolated/nonconductive?

When I look at transistor packages, I see two different heat sink types. One type is in metallic color, the other type is black plastic colored. I read datasheets of some components, none of them ...
3
votes
1answer
260 views

USB + Power: Isolate or not?

I am working on an adapter that will allow a device to be connected to both a PC and external power supply. I am wondering if I will need to isolate the 2 5V supplies with a DC/DC converter and some ...
3
votes
3answers
266 views

DC-DC isolation for my car stereo… Where do I start?

I recently noticed that my jeep's stereo whines with a frequency that seems proportional to the rpm of my engine (and alternator), and is louder when my headlights are on. If my stereo was powered ...
3
votes
3answers
257 views

Ways to isolate DC power source

I need to isolate my circuit from the power source of 5V dc. Since this is for medical use, and the device is powered by USB, the isolation needs to be at least 4kVrms, 5mm clearance, 8mm creapage ...
2
votes
3answers
196 views

I2C isolation; 3kV

I am working on a high-side current sensor, where the high-side is around 3kV. I have come to the conclusion, with some help from you kind folks, that it is best that I float the majority of my ...
2
votes
3answers
156 views

Galvanic Isolation with Voltage Equalization?

I need to equalize the ground voltage between the input and output of an isolated DC-DC power supply while still maintaining galvanic isolation. Is there a way to do this? The reason I need this is ...
2
votes
4answers
244 views

What is an appropiate way to isolate a DC signal?

The question might sound kind of funny, but I'm unsure how else to word it. So... Pictures!! Currently, I have a setup like this: simulate this circuit – Schematic created using ...
2
votes
2answers
55 views

Separating / Isolating the circuit blocks

I was designing the circuit of a superhet receiver, block by block. Needless to say, my concern is how would I separate the various blocks. In other words, how would I interconnect the blocks ( not ...
2
votes
1answer
102 views

How to work out or calculate this circuit?

I'm not an engineer, I understand a lot but I fail to understand how it works and how to calculate this for a 24vdc input: