Pfc + Ups = ???

[ifrythings]

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?


Thanks


Dave.

[star882]

It should work fine.

[switchmodepower]

It should shape the line current to the line voltage.
Should work fine.

[sawreyrw]

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.

[Groman]

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?

[Groman]

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

[Eva]

Modified sinewave UPS will have trouble with the high input capacitance of high power PFC converters. Otherwise, it would work fine.

[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

[switchmodepower]

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?

[Groman]

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