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MAXPAYNE
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« on: October 04, 2012, 12:27:59 12:27 »

What will be the output voltage in this ckt, if I give pure 340V DC input ?

At DC, pf=1, so will it be  equal to the input ? Is there any harm for giving pure DC instead of AC in the ckt ?
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« Reply #1 on: October 04, 2012, 01:43:57 13:43 »

PF is not 1 at DC. It is indeterminate

That said, that circuit boosts voltage based on sensing current and input voltage, boosting voltage until the phase angle is zero.

So what is the phase angle between DC volts and DC? Zero, or infinity and beyond?
« Last Edit: October 04, 2012, 01:49:10 13:49 by solutions » Logged
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« Reply #2 on: October 05, 2012, 06:41:08 06:41 »

PF is not 1 at DC. It is indeterminate

That said, that circuit boosts voltage based on sensing current and input voltage, boosting voltage until the phase angle is zero.

So what is the phase angle between DC volts and DC? Zero, or infinity and beyond?

Normally shape of the voltage after the diode bridge is like halfwave sine. but my question is what will happen if I apply pure Dc at the input ? will the PFC-IC nd MOSFET T will remain inactive ?
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Gallymimu
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« Reply #3 on: October 05, 2012, 07:08:24 07:08 »

Do have have any further information on the PFC IC?  It would be rash to make assumptions on how it behaves at DC.  Though it isn't uncommon to drive power supplies with DC input.

Posted on: October 05, 2012, 06:53:07 06:53 - Automerged

PF is not 1 at DC. It is indeterminate

That said, that circuit boosts voltage based on sensing current and input voltage, boosting voltage until the phase angle is zero.

So what is the phase angle between DC volts and DC? Zero, or infinity and beyond?

Why would the power factor be indeterminate?  If you use the definition of power factor being True power divided by Apparent power it would in fact be 1.  What other definitions of power factor would cause it to be indeterminate?

If you use the ratio of W/VA PF would seem to be 1 for a DC input.

if you go by phase angle of voltage vs current...  The influence of reactive elements as frequency approaches zero goes to zero, not infinity OR beyond Smiley  So I think it is one at DC!

This also holds if you consider the "power triangle" relationship between reactive power, true power, and apparent power.  At DC there is no reactive power so true power = apparent power and their ratio is one.

Certainly indicate if I am missing something obvious in your thought process.

References:
(DC power factor) http://forum.allaboutcircuits.com/showthread.php?t=33047
(DC power factor) http://wiki.answers.com/Q/What_is_the_power_factor_of_a_DC_system
(power factor calculation) http://en.wikipedia.org/wiki/Power_factor
(power factor calculation) http://www.oru.com/energyandsafety/electricdelivery/powerfactor/calculatingpowerfactor.html
(power triangle and power factor calculation) http://openbookproject.net/electricCircuits/AC/AC_11.html

« Last Edit: October 05, 2012, 07:36:12 07:36 by Gallymimu » Logged
solutions
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« Reply #4 on: October 06, 2012, 04:31:41 04:31 »

That circuit does not measure RMS power. The context here is that circuit, not a university lecture. It measures current and voltage, and likely the phase angle between the two.

So, how do you measure the phase angle of DC in a circuit desgined to measure phase angle? It's indeterminate.
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« Reply #5 on: October 06, 2012, 06:17:40 06:17 »

That circuit does not measure RMS power. The context here is that circuit, not a university lecture. It measures current and voltage, and likely the phase angle between the two.

So, how do you measure the phase angle of DC in a circuit desgined to measure phase angle? It's indeterminate.

So it is not possible to put pure dc at the input ?
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« Reply #6 on: October 06, 2012, 12:25:29 12:25 »

Maybe, maybe not. Depends on the design of what's in that box.  The design spec likely did not specify DC operation.

Ask the apps engineers - that's what they're there for
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« Reply #7 on: October 06, 2012, 01:04:29 13:04 »

And what does the data sheet say(why not post the ic number), the ciruit is expection AC input juction R1, R2 is trigger for ic,to trigger input in to T
looks like your using a Power Integrations device, so why not ask Mr. Green what he thinks..
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« Reply #8 on: October 06, 2012, 02:41:09 14:41 »

I wanted to know in generic what will happen for any smps. however my particular application used CM6802 IC (PFC & PWM combo)., where two transistor forward topology is used . This is a computer PSY made by thermaltake.
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« Reply #9 on: October 06, 2012, 03:22:02 15:22 »

Quote
Is there any harm for giving pure DC instead of AC in the ckt ?

I bet, it will be just fine.

-ichan
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Gallymimu
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« Reply #10 on: October 06, 2012, 04:11:27 16:11 »

That circuit does not measure RMS power. The context here is that circuit, not a university lecture. It measures current and voltage, and likely the phase angle between the two.

So, how do you measure the phase angle of DC in a circuit desgined to measure phase angle? It's indeterminate.

Phase angle is 0, not indeterminate.  The whole basis for how this all works "in circuit" is the reactive nature of the components which create the delays that cause the phase angle shift.  What happens to reactance as frequency approaches zero?  Reactance goes to zero and therefore so do the delays and the phase angle.  I provide references for legitimacy and credibility as I am not ALWAYS right, but usually am.  Please share a reference (or some clear math) that says phase angle approaches "indeterminate" as frequency approaches zero.

Sorry don't mean to butt heads with you so much Solutions, but I think you are incorrect some times and we both might learn something new in the discussion!



Posted on: October 06, 2012, 04:04:36 16:04 - Automerged

I bet, it will be just fine.

-ichan

There is some risk, but I agree, it would probably work.  I've driven a lot of AC to DC converters with a DC input in large power supply systems when we needed a low cost internal Aux supply but we wanted to tap off the output of the initial transient protection and rectification circuitry.

It's just hard to know exactly how the PFC circuit will respond with a phase angle of zero.

Now I bet you could disconnect the source of the MOSFET for the output of the PFC circuit and then you would almost certainly be okay since it will no longer be able to shunt current in order to correct power factor.  Don't disconnect just the gate as it could float and cause real problem.  Or just take the MOSFET all the way out.

No guarantees but that's what I'd probably try if you schematic is correct.  If the PFC circuit is well designed it should handle edge cases like 0 phase angle at DC input... BUT as we all know things aren't always well designed!
« Last Edit: October 06, 2012, 04:42:05 16:42 by Gallymimu » Logged
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« Reply #11 on: October 06, 2012, 07:51:55 19:51 »

Actually I am thinking about putting DC at my computer psu during the power blackout. this will simplify the ups design as only a single stage is required i.i. normal 12V > 360V dc-dc converter will do the work. So it is not possible to pull the mosfet out of the ckt...
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« Reply #12 on: October 06, 2012, 08:24:55 20:24 »

Actually I am thinking about putting DC at my computer psu during the power blackout. this will simplify the ups design as only a single stage is required i.i. normal 12V > 360V dc-dc converter will do the work. So it is not possible to pull the mosfet out of the ckt...

Ah I see, interesting idea.  I wish I could tell you more.  If you are comfortable I'd give it a a try and see what happens.  Make sure everything is fused to avoid anything catastrophic I guess. 

You might still be able to pull the mosfet and give up the power factor correction when running on AC.  High power factor is important to the utility companies but isn't that big of a deal for the home user or hardware hacker Smiley

whatever you decide to do please let us know how it goes!!
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« Reply #13 on: October 07, 2012, 02:41:16 02:41 »

Phase angle is 0, not indeterminate.  The whole basis for how this all works "in circuit" is the reactive nature of the components which create the delays that cause the phase angle shift.  What happens to reactance as frequency approaches zero?  Reactance goes to zero and therefore so do the delays and the phase angle.  I provide references for legitimacy and credibility as I am not ALWAYS right, but usually am.  Please share a reference (or some clear math) that says phase angle approaches "indeterminate" as frequency approaches zero.

Again with the math - I know the math.

What's the phase angle of DC using zero crossings?
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Gallymimu
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« Reply #14 on: October 07, 2012, 04:42:44 04:42 »

I understand what you are trying to get at.  You want me to say you can't measure zero crossings on an DC signal so therefore the phase angle is indeterminate.  

It doesn't really make sense to try and use the one invalid method of measurement (what's the zero cross for DC? Never? Always?) to make blanket statement that the feature phase angle can not be determined.

I'll give it a go anyway though... This specific case can still be determined using limits.  What is the limit of phase angle as the frequency approaches zero?

So lets look at the zero crossing point of two waveforms with a delay associated with some reactive elements in the circuit (a simple case like an LPF perhaps?).  The period increases as the frequency decreases and approaches zero.  The percentage contribution of the fixed delay becomes a smaller and smaller percentage of the period.  The ratio (delay/period) approaches 0 as frequency decreases (period increases).  As the period approaches infinity the phase delay (ratio * 360) approaches 0.

So there is an example for zero crossing measurement.  I don't think it's as strong of an argument as direct math like looking at an LPF where the phase delay is  -arctan of omega R * C or some of the other things I mentioned.  It's still pretty conceptually obvious though.


« Last Edit: October 07, 2012, 05:28:20 05:28 by Gallymimu » Logged
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« Reply #15 on: October 07, 2012, 05:57:56 05:57 »

Ah I see, interesting idea.  I wish I could tell you more.  If you are comfortable I'd give it a a try and see what happens.  Make sure everything is fused to avoid anything catastrophic I guess. 

You might still be able to pull the mosfet and give up the power factor correction when running on AC.  High power factor is important to the utility companies but isn't that big of a deal for the home user or hardware hacker Smiley

whatever you decide to do please let us know how it goes!!

The PSU is still have 5 yrs warranty. So I will not modify it inside. Tongue So whatever I do I have to do it externally Smiley

If there is no pfc stage, I am sure that my idea of putting dc will do the job ! Cheesy

neway, Due to lack of oscilloscope I am unable to do any test/modification at the moment. thats why I would like to know what the expert says... Cheesy
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« Reply #16 on: October 07, 2012, 02:54:44 14:54 »

Sadly, the experts never post here  Tongue
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« Reply #17 on: October 07, 2012, 02:59:06 14:59 »

then where they post ? Smiley
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« Reply #18 on: October 07, 2012, 04:24:15 16:24 »

Sadly, the experts never post here  Tongue

Smiley

Posted on: October 07, 2012, 04:22:03 16:22 - Automerged

then where they post ? Smiley

most power supplies are made and designed in Taiwan, so you might want to see if there is a dot TW version of sonsivri you can ask on Smiley  Many of the american power supply experts are in Ft Collins but they typically work on much bigger stuff than computer power supplies.
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