Inductor core question - Electronic Circuits Projects Diagrams Free

elec123 · 22nd October 2007, 01:58 PM

Hi,

Basically i'm building a dc-dc boost converter. With the switch switching at 20kHz.

I have calculated the component values and need a 6.8mH inductor with a saturation surrent of 5.5A or higher.

I have found this.....

http://cpc.farnell.com/jsp/Component...questid=344363

which seems to do just the job, but it doesn't say anywhere what material the core is made of, wouldn't an iron core become lossy at the frequency i want to switch at? been told i need a ferrite or ceramic core inductor....

having trouble finding inductors that can handle this current, can anyone recommend a site supplying them?

Thanks

mneary · 22nd October 2007, 10:20 PM

It might not have a permeable core. That's a lot of inductance... can you tell us more about your circuit? Reverse engineering your numbers, I'm guessing you either slipped a decimal point (or two) or your input is close to 700 volts.

That coil is intended for audio, so it's probably good to 20 KHz. It has an open magnetic field so it'll radiate a lot of interference.

audioguru · 22nd October 2007, 10:39 PM

I think that inductor for a speaker's crossover uses air as its core so it doesn't saturate at high power.

elec123 · 23rd October 2007, 08:22 AM

thanks for your replies, think it will be fine for what i need it for....

mneary, i'm pretty sure my calculations are right, but this is how i got to the inductance value....

I want to boost the output of a solar pv panel (17.7V) to 100V.

k = 1 - Vs/Vo = 0.823

switching at 20kHz Tp = 1/f = 50us

i want the ripple current Il to be 2% of the rated current of the pv panel (5.5A) so Il is 0.11A

rearranging V = L. dIl/dt gives L = Vs.dt/dIl

where dt = k.Tp = 41.15us therefore L = 6.6mH the nearest preferred value is 6.8mH.

Look right?

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22nd October 2007, 01:58 PM	(permalink)
elec123	Inductor core question Hi, Basically i'm building a dc-dc boost converter. With the switch switching at 20kHz. I have calculated the component values and need a 6.8mH inductor with a saturation surrent of 5.5A or higher. I have found this..... http://cpc.farnell.com/jsp/Component...questid=344363 which seems to do just the job, but it doesn't say anywhere what material the core is made of, wouldn't an iron core become lossy at the frequency i want to switch at? been told i need a ferrite or ceramic core inductor.... having trouble finding inductors that can handle this current, can anyone recommend a site supplying them? Thanks

22nd October 2007, 10:20 PM	(permalink)
mneary	It might not have a permeable core. That's a lot of inductance... can you tell us more about your circuit? Reverse engineering your numbers, I'm guessing you either slipped a decimal point (or two) or your input is close to 700 volts. That coil is intended for audio, so it's probably good to 20 KHz. It has an open magnetic field so it'll radiate a lot of interference.

22nd October 2007, 10:39 PM	(permalink)
audioguru	I think that inductor for a speaker's crossover uses air as its core so it doesn't saturate at high power. __________________ Uncle $crooge

23rd October 2007, 08:22 AM	(permalink)
elec123	thanks for your replies, think it will be fine for what i need it for.... mneary, i'm pretty sure my calculations are right, but this is how i got to the inductance value.... I want to boost the output of a solar pv panel (17.7V) to 100V. k = 1 - Vs/Vo = 0.823 switching at 20kHz Tp = 1/f = 50us i want the ripple current Il to be 2% of the rated current of the pv panel (5.5A) so Il is 0.11A rearranging V = L. dIl/dt gives L = Vs.dt/dIl where dt = k.Tp = 41.15us therefore L = 6.6mH the nearest preferred value is 6.8mH. Look right?