# Tag Info

## Hot answers tagged parallel

48

It's the voltage rating on the resistors that is important here. They are powered from rectified 230 V AC and they need to have the correct voltage rating to suit their application. Two resistors in series having an individual rating of 200 V gives a total voltage rating of 400 volts (near enough if you ignore tolerances on values). Take a look at the good ...

38

Because UL 1741 does all the heavy lifting for you. That's what makes it "so easy". UL 1741 is a complicated spec for "grid-tie solar inverters". Aside from doing their usual inverter thing (itself no small matter), a 1741 inverter also senses the presence of the grid, and obviously syncs its output to the grid. A UL 1741 inverter is intentionally ...

32

MOSFETs are a bit unusual, in that if you connect several of them in parallel, they share the load quite well. Essentially, when you turn on the transistor, each one will have a slightly different on-resistance and a slightly different current. The ones carrying more current will heat up more, and increase their on-resistance. That then redistributes the ...

30

Both configurations will conduct power to the loads. When trying to figure out what's 'illegal', and why, you need to understand what fault conditions the authorities are trying to prevent. There may be a commentary in the relevant standards if you're lucky. In the UK, such an arrangement of a circular conductor is called a 'Ring Main', and was actively ...

21

Take a look at this graph: - http://electronicdesign.com/files/29/1478/figure_01.gif Capacitors have a resonant frequency due to the inherent small series inductance they have. The "generalized" capacitor showing the various parasitic components is shown below: - It's the L$_{ESL}$ that causes this series resonance. For a typical 10 uF tantalum ...

21

The problem is keeping the signals on a parallel bus clean and in sync at the target. With serial "all you have to do", is be able to is extract the clock and as a result the data. You can help by creating lots of transitions, 8b/10b, bi-phase or manchester encoding, there are lots of schemes (yes this means you are adding even more bits). Yes, ...

20

Yes, this is exactly the intended purpose. It's called a wired-OR or wired-AND, depending on your logic. (Or, as Tony points out, even a wired-NOR!) However - you should not do this if you just want twice the amount of current sinking capacity. Only if you want the feature of being able to switch using separate inputs. Current will likely not be shared ...

19

Reasons someone might put two resistors in series in a volume design: A bit higher power was needed than what the commonly stocked parts can handle. Let's say a company standardizes on using 0805 resistors unless there is a good reason not to. They therefore end up with many 0805 values in stock, with only a few values of other packages. Now you need a ...

18

Yes. Fixing production errors by using jumper wire is a time honored tradition by those blessed with hindsight. For Power rails or low speed GPIO (Think Push Buttons inputs or LED outputs), a simple wire would work. As a precaution, you could cut the trace, and carry the full load on the jumper you are adding. If the jumper fails, the load would try to go ...

18

Capacitors eventually stop behaving like capacitors at high frequencies and exhibit resistive and inductive effects. The 100pF capacitor filters high frequencies that the 100nF capacitor could not. This is shown clearly on the diagram below which shows the impedance (Red) of a 100nF capacitor and a 100pF capacitor (Light Grey top curve) versus Frequency. ...

18

I tried to replicate, and I saw the same behavior. @SteveG did, too. After a few questions regarding the sanity of each of us, I think I found why, and it is pretty simple: Are you absolutely sure you are actually plotting the right voltage node? In both of your plots, it shows "V(n003)/I(V1)". But I actually realized that if I mess up just a bit with the ...

18

You have two problems Paralleling MOSEFTs in this mode is unstable. However, you could parallel the outputs of several totally independent current sources, each with its own power device, Rs and opamp. Most MOSFETs will not like operating in linear mode like this, they are designed and specified for switching operation. Internally, MOSFETs are hundreds, if ...

17

It is indeed possible to have parallelism on a superscalar processor. A superscalar processor can execute multiple instructions at the same time by using multiple execution units. There are certain limitations depending on the architecture. It is not true parallelism. If you have to calculate $$A = B + C,$$ $$D = A + 3,$$ you cannot execute both ...

17

Two parallel wires with no resistance - why it's wrong? This is wrong because there are no wires with no resistance. When trying to resolve Kirchhoff equations for this loop (or whatever their algorithm is), the simulator would run into division by zero exception. To avoid program crash, it likely analyzes these conditions and declares the circuit as error. ...

17

Yes. It does. Note that in general you can't blindly parallel transistors. You can parallel MOSFETs without special measures since as they get hotter they conduct less well which distributes the load more or less evenly in spite of individual component differences. Positive temperature coefficient. BJTs conduct BETTER as they get hotter so the BJT that ...

17

As DKNguyen pointed out it is important to "account for" or "manage" failures. We put capacitor banks on the 28 VDC power bus of spacecraft all the time. EVERY cap had its own fuse, so if the cap shorted out - which was the predominant failure mode - the fuse would blow and take the cap out of the circuit. We were also concerned about partial shorts of a cap,...

16

This is actually a very common technique to do, both with BJTs (traditional transistors like drawn above) and MOSFETs. With BJTs, you don't need to bother with separate trimmed base resistors, all you need to do is add current sharing resistors or sometimes called ballast resistors. Look at this page for instance, the first one I found with google that ...

16

Why is the serial connection faster than the parallel connection? You're making wrong assumptions. Take any serial connection. Now place 10 in parallel and call that the parallel version. Which one is faster ? So how come the serial connection is considered the future while the parallel one as a thing of the past? Says who ? Parallel connections are ...

16

The shift is from "parallel on a single clock" to "multiple serial links". Such as PCIe, where a card may have 1x to 16x "lanes". There are two factors involved, skew and size. Adding more connectors makes both the cable, its connectors and the receptacles on each device larger and more expensive. Look at how large things like Centronics printer cables and ...

14

I'll assume that the total length of each of your buses is under 1 meter, which is typical for plain I2C and SPI. Also, the bus capacitance is within the spec. There should be only one (1) set of pull-up resistors. As a result, the best place for them is on the main controller board. Don't put the pull-ups on the modules. If you want to have pull-up in ...

14

If your budget is less then 10-20 thousand dollars (or more realistically 100K+), you have no hope of getting an ASIC made. The common device used instead of an ASIC, in situations where you cannot afford the NRE (non-returnable expenses - basically the cost for producing the masks for etching your asic, as well as the design costs), is to use a FPGA. ...

14

It is really not that easy. It's easy for you because standards and regulations have been put in place that affect the power company and anyone selling you grid-tie inverters. The system is designed and regulated by law so that you can just buy a shiny box, pay someone to hook it up, and not worry. The grid-tie inverter is pretty complicated. It has to ...

13

Yes, it is, but the easiest and most compact representation is the $${1\over R_t} = \sum_{i=1}^n {1\over R_i} = {1\over R_1} + \dots + {1\over R_n}$$ you already mentioned. To see the pattern you can do the math yourself for 3 resistors: $${1\over R_t} = {1\over R_1} + {1\over R_2} + {1\over R_3}$$ Do the first addition using the usual method: {1\...

13

By the way, that illustration is terrible. It is showing an inherently DC circuit, with constant draw DC loads, e.g. LEDs. And that is a particular use-case where ring circuits are totally OK. With AC mains, however... It's mainly because complex circuit pathing makes circuits unmaintainable. The neutral must be right next to its partner hot, mainly ...

13

Falstad wants to be able to animate the circuit, showing how much current flows in each wire. In this circuit, that isn't possible, so it is indicating this as an error.

13

You need two back-to-back P-channel MOSFETs for each power input. Here is an example from an Atmel eval board, though you'll want to scale up the MOSFETs considerably, and maybe reduce the resistor values to something like 10K: The VCC_USB input is dominant if both are present (in other words, if only one supply is present, that one will be used, if both ...

13

First off, I want to warn you just a little bit about putting battery systems in parallel. It's usually not a good idea because often the two batteries (or battery systems) don't have exactly the same voltage. If they are different, then the one with the larger voltage will supply some current into the battery with the lower voltage and this often isn't a ...

12

For an application where you need to parallel transistors and control current in a linear fashion (not switching the transistors fully on and off), BJTs are your best bet. As Olin Lathrop says, the circuit will need to have resistors in series with the BJT emitters to help balance current. Here is a starting example circuit to show emitter resistor ...

12

I'm afraid you need to review capacitors. I know that when capacitors are in serial, you add their values. When capacitors are in parallel, their values add Not in serial manner like I was expecting to see. Loosely speaking, a capacitor has "infinite" impedance at DC. So, if the capacitor were in series with the regulator output, there could only be ...

12

No you should not do this. Sometimes it is explicitly allowed on the data sheet (but not that I can see on this data sheet), and when it is, in my experience you never get as much as double the capacity. Paralleling physically separate relays is worse again because they're not physically moving together- expect welded contacts etc. if you tried that. If ...

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