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

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6
votes
4answers
999 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 ...
0
votes
2answers
206 views

How to implement an isolated connection matrix

I need to implement a circuit for a researcher, which looks a little bit like this: Description of the circuit: There are two or more fully isolated biphasic current drivers, and N output pins. ...
1
vote
2answers
360 views

Isolation transformer weirdness

I recently posted a question about cutting the ground wire in an isolation transformer to make it truly isolated. After reading the responses, I decided the best advice was to reconnect the ground ...
5
votes
3answers
713 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 ...
3
votes
3answers
640 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 ...
11
votes
2answers
4k 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 ...
5
votes
1answer
606 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 ...
1
vote
1answer
418 views

How close can I place two transformers?

I need to place two of these transformers in a case. How close am I allowed to place them? Can they touch each other (of course, they will be electrically isolated)? Is their orientation with ...
4
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
1answer
3k 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 ...
4
votes
1answer
143 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?
0
votes
2answers
385 views

Sixteen 100v isolated power supplies

I need to create sixteen isolated power supplies on a single PCB. Input voltage 9v DC. Output voltage 100v DC. Output current 10mA each. No precise regulation needed. Efficiency not terribly ...
3
votes
3answers
283 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 & ...
7
votes
2answers
324 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 ...
9
votes
1answer
981 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 ...
24
votes
3answers
4k 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 ...
1
vote
3answers
240 views

How to hook up an FPGA to a component that has a different power supply?

I recently programmed my FPGA with a logic analyzer core for the purpose of reverse engineering a crappy modem I have. I found on it what I think is either JTAG or TTL-serial pads. There are 4 blank ...
8
votes
4answers
889 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 ...
3
votes
3answers
288 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 ...
6
votes
2answers
905 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 ...
1
vote
1answer
225 views

Isolating BNC connector from test shield

For my project, I need to have BNC connectors on the test metal shield. So what I did so far is drilling holes, and mounting BNC connectors on it: I used some hot shring on the part which passes ...
5
votes
1answer
279 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 ...
0
votes
3answers
1k views

How to make two isolated power sources from one source?

I need to have two electrically isolated power sources. Here are the details of the application: http://revolectrix.fmadirect.com/support_docs/item_1377.pdf page 26: I need to make this work with ...
0
votes
0answers
340 views

Is this buffer for protecting 3.3v logic from 9v power sane?

I'm playing with the idea of making a multi-interface for classic game controllers. The interface connector between the system and the controller has several pins that can be used bidirectionally ...
1
vote
1answer
202 views

Augment battery-run device power with 100mA solar cell?

I may be running a microcontroller for an extended period of time in a portable manner under battery, but do not want its life to be reduced by a silly load such as an LCD screen (5v + backlight) ...
1
vote
1answer
639 views

Need to isolate my ammeter (measuering and powering the unit from same power source)

I have a problem and Im not sure what the best way is to address this. I converted an ATX PC power supply to use as a lab power supply I installed a digital volt meter and a digital ammeter. To power ...
3
votes
2answers
256 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 ...
1
vote
2answers
409 views

what would be the most suitable components to replace some relays?

I'm working on an electronic product based on a microcontroller that must be able to control a series of actuators: 230V AC motors ON/OFF, 24V DC motors ON/OFF, 80V/20A heating element ON/OFF. The ...
4
votes
2answers
324 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 ...
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
1answer
259 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 ...
2
votes
1answer
120 views

Are dual MOSFET devices isolated from each other? If so, to what degree?

I am using an OnSemi NTGD3148N dual MOSFET in a project. I cannot find a specification anywhere in the datasheet stating the isolation between the devices; and this holds true for most dual MOSFETs ...
4
votes
2answers
314 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
637 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 ...
2
votes
3answers
1k views

Switching 120V AC with Digital Logic on Isolated Power Supply

Context: A digital phase-controlled light dimmer system. 120V AC mains I use an isolating transformer (and rectifying circuit) to generate +12V and +5V DC rails. I want to use reverse phase ...
18
votes
4answers
4k 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 ...