spinach
Electrical
- Aug 5, 2008
- 11
Hello,
I am designing an offline Power factor corrected SMPS (continuous mode boost converter at front).
Since it is mains powered, i am worried how i will be able to draw the PFC's high frquency pulse currents through the Line Inductance. (That line inductace being the inductance of the power wires and the Electricity supply company's transformer secondary coil)
I am thinking of putting a big AC capacitor on the line (AC) side of the diode bridge.....however, that worries me because then that will ruin the power factor.
....What i could do is put a capacitor of sufficient value across the input AC line...such that it "cancls" the inductive reactance of the line inductance and makes my power supply look resistive....however, i am worried that such a capacitor would have to be of a value and voltage rating that would make it very expensive.
When i look at circuit diagrams of EMC filters...they confuse me because the capacitor values are always less than 4n7.....is it worth putting these in at all?....
......surely they won't give sufficint energy storage to supply the pulse currents to the switch mode power supply?
Then there's the common mode choke.....that appears to be the only other option for providing the energy storage for the pulse current input to my Switched mode power supply........but i thought that all the common mode choke did was stop currents leaking to earth, and not providing energy storage?
And with the common mode choke, an enginer told me they never saturate and never need a gap in their core, -but surely if they conduct enough current that the magntising current puts a flux in the core which will saturate it, -then it saturates i would have thought.
I have never had this problem before because bfore i always drew the SMPS currents from the caps after the diode bridge.
I am designing an offline Power factor corrected SMPS (continuous mode boost converter at front).
Since it is mains powered, i am worried how i will be able to draw the PFC's high frquency pulse currents through the Line Inductance. (That line inductace being the inductance of the power wires and the Electricity supply company's transformer secondary coil)
I am thinking of putting a big AC capacitor on the line (AC) side of the diode bridge.....however, that worries me because then that will ruin the power factor.
....What i could do is put a capacitor of sufficient value across the input AC line...such that it "cancls" the inductive reactance of the line inductance and makes my power supply look resistive....however, i am worried that such a capacitor would have to be of a value and voltage rating that would make it very expensive.
When i look at circuit diagrams of EMC filters...they confuse me because the capacitor values are always less than 4n7.....is it worth putting these in at all?....
......surely they won't give sufficint energy storage to supply the pulse currents to the switch mode power supply?
Then there's the common mode choke.....that appears to be the only other option for providing the energy storage for the pulse current input to my Switched mode power supply........but i thought that all the common mode choke did was stop currents leaking to earth, and not providing energy storage?
And with the common mode choke, an enginer told me they never saturate and never need a gap in their core, -but surely if they conduct enough current that the magntising current puts a flux in the core which will saturate it, -then it saturates i would have thought.
I have never had this problem before because bfore i always drew the SMPS currents from the caps after the diode bridge.
