Filters

nhuwar · 12th July 2009, 12:52 AM

Hi Guys,

Is there a formula for finding the ripple out of a choke input filter?

If there is can someone tell me it?

Thanks a mill,

Nick

Poindexter · 12th July 2009, 01:23 AM

Yes there is, but it is mathematically rigorous and requires several stages of computation, not to mention a little education in filter theory.  I don't do it that way any more; I just plug my proposed filter into PSUD2, which has this math built into it, and let it tell me the answer.

http://www.duncanamps.com/psud2/index.html

It's free.

Thank you, Ben,

Poinz
AudioTropic

nhuwar · 12th July 2009, 01:35 AM

Ya I know unfortunately I'm on my mac and my pc is down stairs.

Also psud2 can't handle a power supply running 6500 vdc at 2.5 amps.

You see my quandary LOL.

And no it's not for an audio amp, college design project.

Nick

Ty_Bower · 12th July 2009, 01:54 AM

It's not to hard to model power supplies in LTspice. Someone ran it on their Mac using a piece of software called Crossover?

http://www.evilmadscientist.com/article.php/crossover

nhuwar · 12th July 2009, 02:09 AM

The programs are called parallels and fusion. I'm familiar with them just haven't bought one yet.

Oh yes I see the one called crossover too. Still haven't spent the money yet LOL.

Nick

Tom Bavis · 12th July 2009, 02:37 AM

OK, here's an oversimplified method: Assume you're starting with 100% ripple at 120 Hz. You have a voltage divider - choke reactance and capacitor reactance. So let's say you have 3 Henries (2.26K @ 120 Hz) into 16 uF (83 Ohms). That's 27:1 so you're down to about 3.3% p-p ripple.

But PSU designer has no problem with 6500V and 2.5A - and it says about 5% ripple.

nhuwar · 12th July 2009, 02:56 AM

I didn't think you had a choice of a rectifier that went to that high a voltage.

I will play around with it tomorrow.

But thanks for the info Tom.

Nick

Tom Bavis · 12th July 2009, 02:59 AM

You get a warning, but you also get a result. Simulated diodes don't smell quite as bad if you overvoltage them...

nhuwar · 12th July 2009, 02:35 PM

Thats pretty funny.

Oh one other question. For you estimate you did, how did you get 3.3 % from 27:1?

I did the same thing with the components I'm going to use and got 34.2 to 1. Would it be 2.9%?

Thanks,
Nick

Tom Bavis · 12th July 2009, 04:16 PM

Quote:

Originally posted by nhuwar
Thats pretty funny.

Oh one other question. For you estimate you did, how did you get 3.3 % from 27:1?

I did the same thing with the components I'm going to use and got 34.2 to 1. Would it be 2.9%?

Thanks,
Nick

Excuse the mental arithmetic - 1/27 is 3.7%. Still more precision than it deserves, though, as it's a very rough approximation, ignoring loading.

12th July 2009, 12:52 AM	#1
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Filters Hi Guys, Is there a formula for finding the ripple out of a choke input filter? If there is can someone tell me it? Thanks a mill, Nick

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12th July 2009, 01:23 AM	#2
Poindexter diyAudio Member Join Date: Oct 2004 Location: Maui, Hawai'i, USA	Yes there is, but it is mathematically rigorous and requires several stages of computation, not to mention a little education in filter theory.  I don't do it that way any more; I just plug my proposed filter into PSUD2, which has this math built into it, and let it tell me the answer. http://www.duncanamps.com/psud2/index.html It's free. Thank you, Ben, Poinz AudioTropic

12th July 2009, 01:35 AM	#3
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Ya I know unfortunately I'm on my mac and my pc is down stairs. Also psud2 can't handle a power supply running 6500 vdc at 2.5 amps. You see my quandary LOL. And no it's not for an audio amp, college design project. Nick

12th July 2009, 01:54 AM	#4
Ty_Bower diyAudio Member Join Date: Mar 2007 Location: Newark, DE	It's not to hard to model power supplies in LTspice. Someone ran it on their Mac using a piece of software called Crossover? http://www.evilmadscientist.com/article.php/crossover

12th July 2009, 02:09 AM	#5
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	The programs are called parallels and fusion. I'm familiar with them just haven't bought one yet. Oh yes I see the one called crossover too. Still haven't spent the money yet LOL. Nick

12th July 2009, 02:37 AM	#6
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	OK, here's an oversimplified method: Assume you're starting with 100% ripple at 120 Hz. You have a voltage divider - choke reactance and capacitor reactance. So let's say you have 3 Henries (2.26K @ 120 Hz) into 16 uF (83 Ohms). That's 27:1 so you're down to about 3.3% p-p ripple. But PSU designer has no problem with 6500V and 2.5A - and it says about 5% ripple.

12th July 2009, 02:56 AM	#7
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	I didn't think you had a choice of a rectifier that went to that high a voltage. I will play around with it tomorrow. But thanks for the info Tom. Nick

12th July 2009, 02:59 AM	#8
Tom Bavis diyAudio Member Join Date: Jun 2002 Location: Macedon NY	You get a warning, but you also get a result. Simulated diodes don't smell quite as bad if you overvoltage them...

12th July 2009, 02:35 PM	#9
nhuwar diyAudio Member Join Date: Jan 2007 Location: Tomball Texas	Thats pretty funny. Oh one other question. For you estimate you did, how did you get 3.3 % from 27:1? I did the same thing with the components I'm going to use and got 34.2 to 1. Would it be 2.9%? Thanks, Nick

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