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Re: Ferrite chokes & saturation
From: Gary Lau 25-Nov-1997 2023[SMTP:lau-at-hdecad.ENET.dec-dot-com]
Sent: Tuesday, November 25, 1997 6:48 PM
To: tesla-at-pupman-dot-com
Cc: lau-at-hdecad.ENET.dec-dot-com
Subject: Re: Ferrite chokes & saturation
> From: Gary Lau 21-Nov-1997 1839[SMTP:lau-at-hdecad.ENET.dec-dot-com]
> My ferrite torroid cores are 3.25" OD,
> 2.25"ID, 0.50"T, insulated with .04" LDPE & hot melt glue, wound with 51
> turns LDPE insulated 22AWG, measuring 14mH. Could one generalize about
> the likelyhood of saturating with 250mA peak 60Hz current (15k/60mA w/
> resonant charging est.)?
To answer my own question, I set up a test fixture with a DC power supply,
pulse generator, scope, switching transistor with 1 Ohm emitter resistor,
and choke-to-be-tested with flyback diode in collector circuit.
Observing the current by looking at the voltage across the resistor, in a
perfect inductor, the waveform would be a perfectly linear ramp until the
transistor saturates or power supply limits. With my choke, the waveform
was linear up to about 250mA, somewhat more steep to about 400 mA, and
steeper still beyond this. Saturation appears not to be a black and
white situation, but a gradual decrease in inductance above a certain
current level. Looks like I just make it!
Gary Lau
Waltham, MA USA