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Old 16th October 2010, 05:50 AM   #21
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And a question there?
So, will a UCD work even w/o the phase lead n/w? i mean it should crossover 180 at some freq (obviously< fs) using the parasitics of the actual devices used (comparator, GD and MOSFETS)??
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Old 16th October 2010, 05:56 AM   #22
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Quote:
Originally Posted by newvirus2008 View Post
Is that right ?
Just read 500 or 600 instead of 455kHz.

And the phase lead n/w is to push the phase crossover freq to the desired value........okokok
Even i think i ll need a scope
Thanks for the delay circuit. From simulation, your delay is close to a 700ns one.

Cheers,
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File Type: gif delay.gif (98.8 KB, 299 views)
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Old 16th October 2010, 05:59 AM   #23
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Quote:
Originally Posted by newvirus2008 View Post
And a question there?
So, will a UCD work even w/o the phase lead n/w? i mean it should crossover 180 at some freq (obviously< fs) using the parasitics of the actual devices used (comparator, GD and MOSFETS)??
I do think it will oscillate without phase lead network.

Last edited by gogowatch; 16th October 2010 at 06:02 AM.
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Old 16th October 2010, 06:08 AM   #24
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gogo, change 265pf to 200pf or near.

Does this type of modelling (allpass filter) of comparators etc. work well ? Interesting.

If it does then its simply time delay = d/domega [phase (radians)]

Last edited by newvirus2008; 16th October 2010 at 06:14 AM.
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Old 16th October 2010, 07:37 AM   #25
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Quote:
Originally Posted by newvirus2008 View Post
gogo, change 265pf to 200pf or near.

Does this type of modelling (allpass filter) of comparators etc. work well ? Interesting.

If it does then its simply time delay = d/domega [phase (radians)]
Here it is.

Cheers
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File Type: gif phase-shift-analysis-200pF.gif (98.4 KB, 282 views)
File Type: gif phase-shift-analysis-30pF.gif (98.2 KB, 263 views)
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Old 16th October 2010, 07:50 AM   #26
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ok so its 30pf
ok and 400ns at what freq?
But when i cascade this delay ckt (c=30pf) with LC filter and phase lead n/w, the 180 deg trip-point is above 2 MHz.
But with c=200pf, its 578kHz.....any idea????

let me remind you that i was using an ideal opamp!!!!!!!!

So dont you think that this allpass circuit maybe used to precisely adjust the switching frequency of the UCD ?

Last edited by newvirus2008; 16th October 2010 at 08:06 AM.
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Old 16th October 2010, 08:15 AM   #27
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Ok so approx delay of LM319+BC546+IR2110+IRF530= 200-300ns maybe 250 ns.
switching freq = 250 kHz.

So what delay ckt for 250ns?
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Old 16th October 2010, 08:52 AM   #28
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Originally Posted by newvirus2008 View Post
Ok so approx delay of LM319+BC546+IR2110+IRF530= 200-300ns maybe 250 ns.
switching freq = 250 kHz.

So what delay ckt for 250ns?
This is pretty close up to 1MHz.

Cheers,
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File Type: gif delay-2.gif (96.5 KB, 255 views)

Last edited by gogowatch; 16th October 2010 at 08:58 AM.
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Old 16th October 2010, 01:43 PM   #29
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Thank you gogo!!!!!!!!!

Have a look at my delay model for 250ns and 250kHz.

Will it work?
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File Type: jpg newdelaymodel.jpg (46.4 KB, 239 views)

Last edited by newvirus2008; 16th October 2010 at 02:06 PM.
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Old 17th October 2010, 05:15 AM   #30
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Quote:
Originally Posted by newvirus2008 View Post
Thank you gogo!!!!!!!!!

Have a look at my delay model for 250ns and 250kHz.

Will it work?
My sim using your model showed oscillation at 560KHz instead.

Cheers,
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