when i am alowed to use phasors - Electronic Circuits Projects Diagrams Free

transgalactic · 19th July 2009, 11:08 AM

Vc''+Vc=3cos(2t)
Vc(0)=2
Vc'(0)=3

i was told that some thing should converge on t->inf

is it the ZIR ?

MrAl · 21st July 2009, 05:02 PM

Hi,

Looks like the DC component.

dknguyen · 22nd July 2009, 05:16 AM

What do you mean when do you use phasors? THey're just another way to write complex numbers.

MrAl · 24th July 2009, 04:27 AM

Hi DK,

I was a little confused by this last question too.
We havent heard from transgalactic for a while now, i wonder if he/she
took off to some other galaxy by now :-)

blueroomelectronics · 24th July 2009, 03:35 PM

I think they allow phasors but have banned disruptors

Thunderchild · 29th July 2009, 10:08 PM

just set them to stun and you will be ok (nobody gets killed just stunned)

transgalactic · 30th July 2009, 07:55 AM

i was told that when i have a sinus input in m diff equation
than there are case when i am not allowed to use
foorier transformation(phasors)

but i have to solve it like a normal diff equation with a sinus in the right side

what is that case?

q5101997 · 5th August 2009, 01:50 PM

Phasors can be used in any circuit with a phase shifted power source. They can not be used in underdamped step input circuits because the exponential component adds its own phase component to the ringing component, so:
What equation for Vc can you add to its 2nd derivitive to get 3cos(2t)?

Well, if Vc = Acos(βt) then Vc' = -Aβsin(βt) and Vc'' = -Aβ²cos(βt) so that:

-Aβ²cos(βt) + Acos(βt) = 3cos(2t)
A(-β² + 1)cos(βt) = 3cos(2t)
so: β = 2
and: A(-β² + 1) = 3
A = 3/(-2² + 1)
= -1
so: Vc = -cos(2t) V
I guess the right hand waveform is shifted 180deg from the solution, which makes sense since the equation uses a second derivitive, and therefore shifts the waveform by two lots of 90deg.

Am I right?

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19th July 2009, 11:08 AM	#1
transgalactic	when i am alowed to use phasors Vc''+Vc=3cos(2t) Vc(0)=2 Vc'(0)=3 i was told that some thing should converge on t->inf is it the ZIR ?

21st July 2009, 05:02 PM	#2
MrAl	Hi, Looks like the DC component.

22nd July 2009, 05:16 AM	#3
dknguyen	What do you mean when do you use phasors? THey're just another way to write complex numbers. __________________ Tanaka Sensei (avatar) says: Please spell it "ridiculous" correctly! Not "rediculous". ^^

24th July 2009, 04:27 AM	#4
MrAl	Hi DK, I was a little confused by this last question too. We havent heard from transgalactic for a while now, i wonder if he/she took off to some other galaxy by now :-)

24th July 2009, 03:35 PM	#5
blueroomelectronics	I think they allow phasors but have banned disruptors __________________ Bill Smart Kits build Smart People http://www.blueroomelectronics.com/

29th July 2009, 10:08 PM	#6
Thunderchild	just set them to stun and you will be ok (nobody gets killed just stunned) __________________ I AM the exeption that disproves the rule in many ways but the rules still apply (unfortunately) www.simonsphotography.org.uk/ - My other hobby www.rushdenrotaract.org.uk/ - make a difference and have fun ! Never buy "Trust" products, all mine broke !!!

30th July 2009, 07:55 AM	#7
transgalactic	i was told that when i have a sinus input in m diff equation than there are case when i am not allowed to use foorier transformation(phasors) but i have to solve it like a normal diff equation with a sinus in the right side what is that case?

5th August 2009, 01:50 PM	#8
q5101997	Phasors can be used in any circuit with a phase shifted power source. They can not be used in underdamped step input circuits because the exponential component adds its own phase component to the ringing component, so: What equation for Vc can you add to its 2nd derivitive to get 3cos(2t)? Well, if Vc = Acos(βt) then Vc' = -Aβsin(βt) and Vc'' = -Aβ²cos(βt) so that: -Aβ²cos(βt) + Acos(βt) = 3cos(2t) A(-β² + 1)cos(βt) = 3cos(2t) so: β = 2 and: A(-β² + 1) = 3 A = 3/(-2² + 1) = -1 so: Vc = -cos(2t) V I guess the right hand waveform is shifted 180deg from the solution, which makes sense since the equation uses a second derivitive, and therefore shifts the waveform by two lots of 90deg. Am I right? __________________ Invention is 1% inspiration, 99% perspiration.