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Old 11th September 2007, 09:20 PM   #1
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Default Pfc + Ups = ???

Would a power supply with PFC work properly on a UPS that outputs either a "stepped sinewave" or "modified sinwave"?

I ask because if PFC is supposed to line current look like a sinewave what would it do on the other type of waveforms?


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Old 12th September 2007, 03:31 AM   #2
star882 is offline star882  United States
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It should work fine.
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Old 12th September 2007, 03:46 AM   #3
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It should shape the line current to the line voltage.
Should work fine.
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Old 12th September 2007, 04:20 AM   #4
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Most PFCs are designed so that the input current 'tracks' the input voltage. If the voltage is not sinusoidal, the current will be distorted. I don't think this will work well.
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Old 27th December 2007, 06:26 AM   #5
Groman is offline Groman  Turkey
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Default PFC output

I would like to discuss the output of PFC circuits. Do you know what should be the output ripple voltage frequency? I think it should be 100Hz if we use 50Hz Single Phase 220Vac Source?
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Old 27th December 2007, 07:27 AM   #6
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reply to ifrythings...

if your line voltage is sine wave then your current has to be sine wave to get PF=1 ) if your line voltage is not sine wave for example its stepped sinewave or something different; then your current wave should be also same with it. Point is you should analyse inductor wave form and PWM outputs(Duty Cycle) which give you a good starting point... Think that line voltage(PFC input voltage ) is constant at some time interval delta (t) as a result

dV=L*di/dt
di/dt must be constant which means currnet is triangler wave

peak current value is delta(t)*V(constant) / (L)

You should ask your control chip to make input current constant at delta(t) time interval. However you have triangler sample.....

As a result PFC should not work
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Old 27th December 2007, 09:25 AM   #7
Eva is offline Eva  Spain
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Modified sinewave UPS will have trouble with the high input capacitance of high power PFC converters. Otherwise, it would work fine.
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Old 29th December 2007, 10:51 AM   #8
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Hi Eva,

I am desiging of a PFC circuit. Before connecting it to universal input i am supplying a DC input 116Vdc to analyse everything is fine or not. Problem is MOSFET is being damaged somehow. I didnt understand why. Could you help me
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Old 29th December 2007, 02:06 PM   #9
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Quote:
Originally posted by Groman
Hi Eva,

I am desiging of a PFC circuit. Before connecting it to universal input i am supplying a DC input 116Vdc to analyse everything is fine or not. Problem is MOSFET is being damaged somehow. I didnt understand why. Could you help me

Can you post a schematic?
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Old 30th December 2007, 07:48 PM   #10
Groman is offline Groman  Turkey
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Hi,

The schematic is the same with the page 4 at below link

http://focus.ti.com/lit/an/slua177a/slua177a.pdf

i am using UC3854A

It seems trr of boost diode cause output cap to decharge on mosfet but i am not sure
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