As I said in my post, in order to limit R4 to 1W you must limit the voltage to 7,07V.

With that voltage R4 dissipates 1W and the other 3 resistors less than that, so it is the limit of the circuit.

Of course, with more than 7.07V R4 would overheat, smoke and burn.

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E Cerfoglio
Buenos Aires
Argentina

 

Like me, HiTech was quoting the maximum dissipation of the circuit - NOT how much it would dissipate as connected.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

Yes you are correct.
Using 1W resistors, the voltage must be limited to 7.07V then R4 dissipates its max of 1W and the remaining resistors dissipate 1.666W.
Then the total dissipation is 1.666W which certainly is less than 2W.

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Uncle $crooge

 

Hi
Sorry because of my late reply

Thank you all guys for your response

I did some calculations and now I understand what I need

Once the tow branches have different values 50 Ohm & 75 Ohm

So there must be a difference in the watt capacity in order to have 4W 30 Ohm resisor

I did the calculations in order to have the new wattage for each resistor
So I found that

Pr4=2.4 Watt
Pr2=1 Watt
Pr1=Pr3= 0.26 Watt

Thanks again

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I’m from Syrian Arab Republic where lots of guys are trying to do better in electronics.

 

Your stupidity goes beyond all my expectations
(Bothered by such a simple task)

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Luis German

 

I don't see why people here should do primary school arithmetic for other people? - I pointed out he was in error, so he would know to look further.

I also suggest you don't be rude to moderators!.

__________________
PIC programmer software, and PIC Tutorials at:
http://www.winpicprog.co.uk

 

WTFingF is with some people?! Everybody knows that geeks and nerds tend to have lower social skills, but this sort of pointless and repeated flaming is just ridiculous.

Re the question and the matter of answering it, I'd agree with HiTech here: it's not just doing the maths but having a decent sense of how to apply it. I think that sort of thing comes with practice, and when you're new it's easy to slip up.

Tronicbrain: You saw that the actual resistance value was correct at least, the problem was just that R4 will dissipate more power than it is rated for. HOWEVER, you could replace R4 with 4 resistors of the same type: 2 in series, in parallel with another 2 in series. That set of resistors would have the same total resistance (50hm: ), but could dissipate 4x as much power. (unless I'm more sleep-deprived than I realise!)

So anyway, you could make this whole 30hm: network of resistors you're describing with 7 instead of 4 (I presume you understand how), and it would AFAICT be ok. Whether or not it's worth the bother and circuit space is up to you Perhaps it's a hypothetical question instead of a practical one though.

 

So, people can't be rude to you because your a moderator, but you can be rude to kids trying to learn about electronics?

Go cry to someone else.