I am looking to build a 5V switching regulator using the 34063. I found a schematic that calls for a 220uh coil.

I have a dead usb charger that uses the 34063. It was using a magnetic core coil.

I found these

http://www.ebay.com/itm/100PCS-DIP-...414?pt=LH_DefaultDomain_0&hash=item564da6f38e

Very cheap. Can they be used for my regulator?

 

You don't know the most important specs for the inductor: current rating and design frequency.

 

You can't use that one, that is the resistor-type inductance, it's not for the oscillation.

Aaccording your current that you choose the type you need.

You should buy like this.
http://www.ebay.com/itm/3-pcs-Magne...648?pt=LH_DefaultDomain_2&hash=item231fc52328

OR like this :

http://www.yunwt.net/5ele_diy/e04.htm

MC34063A development aid.
http://www.nomad.ee/micros/mc34063a/

 

This circuit is actually based on said IC. Performing a long-time test.
You can use the RF inductors, but only for some 10mA.
And really depends on the value.

It is a difference if you use a 12uH RF inductor or 220uH.
12uH has much lower resistance. So they can be used for small PCBs.

For 220uH, you rather need a larger pot core like in the photo.
Consider the nominal max. current, and generously multiply that by factor 2 (also depends on the stepping ratio).

If you choose a too low current rating, you can end up with pretty bad efficiency (and thus, heat developement). DC/DC circuits need some headroom for the coil if you want max. efficiency. This is due to various reasons such as magnetic saturation, and Ohm's DC resistance of the copper wire.

 

It is just to power a pic so my current needs will be very minimal.

My input voltage will be 8-13.5 vdc.

And be fairly efficient since it is being powered off of a SLA battery which also powers a LED spotlight. So the more efficient the better.

Any suggestions?

 

I've used inductors that size up to a couple of hundred mA, it depends on their DC ohms, which unfortunately are not listed in the ebay advertising.

My experience with that size inductor and 220uH is that the DC ohms would probably be under 3 ohms, so I would expect it to be good for 100mA or quite a bit more, definitely enough to run a PIC.

Along with the DC ohms spec those type inductor should have a max DC current spec, because they have really fine wire they will "fuse" with too much current.

Here's a link to a 5v buck converter that used a worse inductor (1500uH 8.7 ohms) that was perfectly ok to 100mA or so;
http://www.romanblack.com/smps/a00.htm

 

I've used inductors that size up to a couple of hundred mA, it depends on their DC ohms, which unfortunately are not listed in the ebay advertising.

What size? The one I posted?

Thanks for he link BTW.

 

http://www.ebay.com/itm/20PCS-PIN-Power-Inductors-220UH-8-10MM-RoHS-PINPowerInductors-/140604501647

this is what you need

RF inductor - 50mA max.

 

What size? The one I posted?

Thanks for he link BTW.

There was a photo of it on the page I linked to, here's the photo;

... RF inductor - 50mA max.

Yeah some brands will state a very low current rating for all the inductors in that size, but the truth is that the lower inductance values use less turns and thicker wire.

Like I said I've had good experiences with 100mA + and no problems. Even with the 8.7 ohm inductor on my page at 100mA 8.7 ohms that's only 87mW heat in the inductor. With a 220uH inductor it's probably 3 ohms or less so 100-200mA should be no problem.

At "running a PIC" type currents (10mA?) those few ohms in the RF style inductor won't really cost you much efficiency.