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Iron core for PFC choke

Y

Yzordderex

Jan 1, 1970
0
Don't really know too much about PFC, other than how it's supposed to
work.

I have TI development board in front of me and it looks like TI used a
Powder Iron inductor for their 250w design. Would laminated steel
core work ok for continuous current mode pfc?

Application is for 230v motor drive. I expect to probably go from FHP
to about 5hp-10hp with the single phase designs.

I am just beginning the r&d phase of this pfc exercise and thought I
would throw this out and see what happens. Any input on materials I
should look at or design tricks/comments most welcome.

regards,
Bob
 
I

Ian Stirling

Jan 1, 1970
0
Yzordderex said:
Don't really know too much about PFC, other than how it's supposed to
work.

I have TI development board in front of me and it looks like TI used a
Powder Iron inductor for their 250w design. Would laminated steel
core work ok for continuous current mode pfc?

No.
Assuming you'r talking about a switched-mode PFC design, the inductor
carries a huge high frequency component.
A laminated steel core will melt.
 
J

John Popelish

Jan 1, 1970
0
Yzordderex said:
Don't really know too much about PFC, other than how it's supposed to
work.

I have TI development board in front of me and it looks like TI used a
Powder Iron inductor for their 250w design. Would laminated steel
core work ok for continuous current mode pfc?

Application is for 230v motor drive. I expect to probably go from FHP
to about 5hp-10hp with the single phase designs.

I am just beginning the r&d phase of this pfc exercise and thought I
would throw this out and see what happens. Any input on materials I
should look at or design tricks/comments most welcome.

regards,
Bob

Is this application design available from the TI web site? It would
help a lot if I could see the circuit you are dealing with.
 
Y

Yzordderex

Jan 1, 1970
0
Ok, thanks Ian. Carrier probably going to be fairly low, so thought I
might have been able to get away with steel. I guess powder iron or
some variant is probably what it's going to be.

regards,
Bob
 
Y

Yzordderex

Jan 1, 1970
0
John Popelish said:
Is this application design available from the TI web site? It would
help a lot if I could see the circuit you are dealing with.

The TI app note is SLUU077C - July 2001
The board uses a UCC3817 controller.

regards,
Bob
 
I

Ian Stirling

Jan 1, 1970
0
Yzordderex said:
Ok, thanks Ian. Carrier probably going to be fairly low, so thought I
might have been able to get away with steel. I guess powder iron or
some variant is probably what it's going to be.

Low?
Depending on the frequency, you just might get away with it, but need
extra cooling.
 
J

John Popelish

Jan 1, 1970
0
Yzordderex said:
The TI app note is SLUU077C - July 2001
The board uses a UCC3817 controller.

I assume the inductor in question is L1, the energy storage
inductor/20:1transformer. This device has to be a pretty efficient
inductor, not at line frequency, but at the chop frequency of the
boost converter, so a laminated metal core is probably not cost
effective.

According to the data sheet

http://focus.ti.com/lit/ds/symlink/ucc3817a.pdf

and the component values on this board, the shorting switch is
operated at about .6/(Rt+Ct)=88.5kHz.

L1 would have to be made of very thin laminations of some probably
exotic alloy, and be gapped to handle that kind of frequency, though a
gapped ferrite core might work as well as a powdered metal core,
though the powdered metal core probably would have a higher maximum
flux capability . The boost converter raises the rectified line
voltage by shorting this across the inductor, till the inductor
current rises to an appropriate (proportional to the instantaneous
line voltage) level, then the shorting switch is turned off, and that
current is delivered to the output capacitor as the energy in the
inductor winds down. The output voltage is regulated only on average
over a half cycle, as ripple voltage is necessary for it to absorb the
varying line current.
 
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