I am designing a board and the problem I am facing on the board hardware is that the core power supply and ground has very low impedance of around 0.3 Ohm. This is leading to a conclusion of two nets as if these are shorted together. Although the current drawn for that particular assembly for core power supply is 9A the impedance would be low(may be around 4-5 Ohm).But is 0.2 Ohm a correct value. We have done the x-ray analysis of BGA, and no solder bridging is observed. Can anyone suggest what could be the issue?
121975
Note that this is a theoretical question - there is no schematic I can show. I will show some schematic, but it will be a very simplified version of an actual circuit, only for illustration purposes.  Assume I have a voltage converter that takes as an input my main voltage (from a power supply) and outputs a certain voltage, for example 1.8V. It would look something like this:         &ndash; Schematic created using   When connecting my circuit to the P.S, I notice it draws too much current (the P.S shows that).  Since I have multiple voltage converters in my circuit (not shown here), I check resistance between each output of each converter to ground. I see that the resistance between 1.8V to ground is almost 0 Ohms. Now I know the fault is either in the voltage converter or one (or more) of the other components drawing power from that 1.8V.  I desolder the resistor shown in the image to disconnect the converter from the other components and see that the converter is fine, but checking resistance from the point connected to all those components still shows 0 Ohms.  My question is - how would you check which component is the faulty one, without desoldering each suspicious component? As you can see in the image, the 1.8V supply is connected directly to the components, without a resistor/bead.  For the sake of this question, assume I have access to whatever equipment needed (no matter how pricey). I wouldn't want solutions to be limited due to availability of equipment.  Thank you!
101729
Does anyone know if a finite number of parallel-series impedance has a general solution?  I am trying to model a network flow problem that can be described in electrical terms and represented as a finite discrete transmission line with arbitrary impedance.  While it is not difficult to write the equations down for a small number of terms, I'm curious if there are some general solutions or insights into the problem.  It looks like  ----Z1---+----Z3---+----Z5---+---...---+          |         |         |         |          Z2        Z4        Z6        ZN          |         |         |         | ---------+---------+---------+---...---+   All the Z's are, in general, different.  I'll need to know the "current" and/or "voltage" at every branch. In this case the bottom is grounded.  What would be cool is to be able to know the voltage and/or current in terms of i, the ith position (the top +).  Any ideas?
103804
I've come across a design where each pad was connected using 4 'bridges' to the GND copper layar. What stands behind these 'bridges'? Why not make a full copper layer with only solder-mask defining the pads?
85984
How do I know when to use lead, flux-core, lead-free, or any other kind of solder out there? Do you have any tips on solder gauge for specific applications?
77696
In the , the both 33nF capacitors , 1K resistor and 0.1uF capacitor are connected to GND. I'm not sure where should I connect those ends of components marked with GND symbol, (To Live, To Natural or the DC GND). I can't read Chinese, I don't really know what everything mean there.  Live directly connects to the shunt resistor and this means that live is also GND (0 volt reference) for the chip? Should I connect those end of components marked as GND symbol to Live wire?
101875
Here is a schematic of a Basys-2 board's power regulator IC and filters. It is just an example but this is fairly similar to many designs I've seen.  Why are there so many capacitors added in parallel rather than just one big capacitor? Can someone give me pros and cons of adding many many capacitors in parallel rather than one big capacitor for each supply net?
122477
I have 12V, Use these 12V to power a device (that has a 12V output signal) and to power a 7805. After the 7805 there is a pic microcontroller where I would have to connect the output from my device. I was thinking of having 2 resistors in a 3/1 ratio in order to have about 4V at the pin of the pic. Can this be done, given that the ground is common, or will it give some sort of problem with the lm7805?
40154
I was trying to solve this unbalanced Wheatstone bridge and found that the current $i$ in the mid wire is 9A .This result was achieved by using node voltage method.    Then I rearranged the same circuit to the form shown in the second image.  and at this point I flipped the right half of the circuit so as to obtain the equal resistors on the same side.    now I again rearranged the circuit as shown.    Here, the final circuit  is a balanced Wheatstone bridge and thus the current i must be 0.  So clearly something went wrong in there.  I saw a post  before this one just to make sure that there is no mistake in rearranging the circuit in the way I have done.   It was answered by the user PhillipWood as being correct and was unfortunately put on hold.  So can someone please point out what exactly went wrong with the above method.
120667
I have a power supply that buzzes when nothing is connected and is silent when there is a power drain. What could it be?  It's a PC power supply that I used to power an LCD through its 12 V line.
45586
This is an attempt to craft a good general question and answer for a topic that's been asked before, but only in specific situations.    Could you describe what I need to know, prior to laying out a PCB board for a differential signal pair with a specified "differential impedance"?  Differential pairs are used for various high speed serial buses, including USB, MIPI, RS-422, RS-485, PCI Express, DisplayPort, LVDS, HDMI and more.  What's the definition of "differential impedance"? On a PCB board, do I need to twist or alternate the wires, as is done for differential pairs in a cable?  Is the impedance of each length matched trace half the "differential impedance", or is it more complicated that that?  How close must length matching be, given the maximum signal frequency?  References that may be of help:
87975
I built the following circuit, a reference VIPer22A circuit.    It works fine but I have a little problem. It gives an electric shock on the secondary side. It's not a "line" shock (sticking your fingers into an outlet), but rather, a "tingly" shock if you touch the device while you're grounded.  It's the same thing that happens when you have an PC power supply not connected to mains earth.   The obvious solution would be, of course, to connect the secondary GND to Earth. The problem I have with this is that this is an audio amplifier, so I'd rather leave GND floating.  Is there a way to eliminate this shock? Capacitively connecting GND to EARTH? Or should I just connect my circuit's ground to Earth?
79810
I know the path of least reisistance has been clarified already However, to derive the equations you need to assume that the voltage of each parallel component is equal. But we know for a short circuit current the voltage is zero (By Ohm's law!) So there is a glaring contradiction!
69043
My current setup is an ESD mat and ESD wristband both connected via alligator clips to unpainted screws that are screwed into a secondary PC power supply (not mounted in a PC case.) This power supply is then connected to an outlet. Would this be a good solution to be safe from static discharge and component safety from it?   I use regular screwdrivers and some of them are from a gunsmithing set, some from an electronics set. Would these screwdrivers cause damage since they are not specified ESD safe? Wouldn’t me touching the screw drivers ground them to the same level as me?  Is this a good set up to prevent ESD damage to components?  Are ESD safe screwdrivers and tools necessary in this case?
117146
I would like to know how to understand/analyse the circuit below. And sorry but my level in electronics is not that high and I could only tell that the opposing transistors on the left are meant to cancel any current from the input , yet I don't really understand the B stage which I think the C stage is well related to , and if I wanted to analyse the nodes around the circuit apart from (A,B,C) How can I do it ?  Is it by measuring the current on resistors/nodes?  and note that the output voltage of the circuit in node C is zero this is what it meant to be.I would appreciate any help.  Regards
71074
It seems common that PBX and other telephone hardware use a positive-ground power supply, where the "hot" line is at -48v.  What's the reason for that?
113860
Can I use a 12 V power supply as the source of electricity for this circuit? And where do I connect the positive/negative of my power supply?  I'm a bit new to this so please understand, thank you.
71347
I'm just a dabbler in electronic circuits and I'm really still kind of a noob. I am working on a project called the "Atari Punk Console" (Originally known as the "Stepped Tone Generator") but there are some parts of the wiring schematic that I don't understand, specifically the parts with the ground symbol.  Here is the schematic:   See those two ground symbols? I don't understand how to properly connect the circuit to ground at these points. How can I do this and be sure that I did it properly. I don't understand grounding at all so any pointers or clarification is also welcome. Thanks in advance.