Power factor correction

Stefano · 11th July 2008, 07:59 PM

Hi to you all!
Is it possible to implement a PFC system on an zen or an aleph? Since they could have a constant current absorbition from the mains I think it would be possible...
What do you think about?

flg · 11th July 2008, 10:06 PM

It seems to me, you can not have constant current draw from the mains. When the mains voltage crosses zero, how does current flow?
The PFC circuits I've seen, ussually boost the AC mains voltage to 400VDC while allowing the input AC current to follow the input voltage. Hence, a power factor of close to 1. Or, zero distortion of the input sinewave. Then. another switching converter, a buck or a flyback, is driven by the 400 volts DC to output something lower. This output could be the rails for the amp.
How would that fit into what you have in mind?

woody · 12th July 2008, 01:11 PM

I have also wondered about the pcf correction. Well I just did a
couple of measurements using a single polarity power supply
using a 33v transformer bridge rectifier and 15,000uf cap loaded
with a big 10ohm resistor. Using a cheap dvm my measurements
are a little confusing to say the least I assume it just doesn't
measure worth a flip........

The transformer measured 1.45A input with 120v AC = 174w
42.8v dc at the filter cap
The power resistor pulled 4.28 A at 42.8v = 183W

and the bridge is dissipating about 5w so 174w in and 184w
out so my meeter is not up to the task or I have solved the energy crissis!

flg · 12th July 2008, 01:58 PM

My guess would be, the meter you're using is not a "true RMS" meter. That would probably be a better measurement.
Because the actuall current draw in a typical "analog" Pwr Supply will look like short duration, high current peaks at the top of the 50/60 cycle sinusoidal voltage peak, your meter is averaging inaccurately. There are also V-I phase changing fuctions happening but I don't want to try to explain that stuff. This is basically because the system can maintain the output voltage fairly well while the caps hold it up. Therefor, very little current is demanded the majority of the cycle. But when the next cycle comes along and gets near peak voltage, greater than the caps, then the caps get recharged with a short duration high current peak. If there were no caps in the system, the current draw would be more continuos and longer duration with lower average current, but the ripple would be rediculous

There would also be some losses in the xfmr and in the esr of the caps that you are not accounting for

11th July 2008, 07:59 PM	#1
Stefano diyAudio Member Join Date: Jun 2002 Location: Cagliari, Sardinia	Power factor correction Hi to you all! Is it possible to implement a PFC system on an zen or an aleph? Since they could have a constant current absorbition from the mains I think it would be possible... What do you think about? __________________ Let's make something special

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11th July 2008, 10:06 PM	#2
flg diyAudio Member Join Date: Jul 2005 Location: North East	It seems to me, you can not have constant current draw from the mains. When the mains voltage crosses zero, how does current flow? The PFC circuits I've seen, ussually boost the AC mains voltage to 400VDC while allowing the input AC current to follow the input voltage. Hence, a power factor of close to 1. Or, zero distortion of the input sinewave. Then. another switching converter, a buck or a flyback, is driven by the 400 volts DC to output something lower. This output could be the rails for the amp. How would that fit into what you have in mind?

12th July 2008, 01:11 PM	#3
woody diyAudio Member Join Date: Jan 2002 Location: Tyrone Ga. U.S.A.	I have also wondered about the pcf correction. Well I just did a couple of measurements using a single polarity power supply using a 33v transformer bridge rectifier and 15,000uf cap loaded with a big 10ohm resistor. Using a cheap dvm my measurements are a little confusing to say the least I assume it just doesn't measure worth a flip........ The transformer measured 1.45A input with 120v AC = 174w 42.8v dc at the filter cap The power resistor pulled 4.28 A at 42.8v = 183W and the bridge is dissipating about 5w so 174w in and 184w out so my meeter is not up to the task or I have solved the energy crissis!

12th July 2008, 01:58 PM	#4
flg diyAudio Member Join Date: Jul 2005 Location: North East	My guess would be, the meter you're using is not a "true RMS" meter. That would probably be a better measurement. Because the actuall current draw in a typical "analog" Pwr Supply will look like short duration, high current peaks at the top of the 50/60 cycle sinusoidal voltage peak, your meter is averaging inaccurately. There are also V-I phase changing fuctions happening but I don't want to try to explain that stuff. This is basically because the system can maintain the output voltage fairly well while the caps hold it up. Therefor, very little current is demanded the majority of the cycle. But when the next cycle comes along and gets near peak voltage, greater than the caps, then the caps get recharged with a short duration high current peak. If there were no caps in the system, the current draw would be more continuos and longer duration with lower average current, but the ripple would be rediculous There would also be some losses in the xfmr and in the esr of the caps that you are not accounting for

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