I want to build a 3A switching regulator circuit (12V to 4.5V) which uses a 1N3880 fast recovery diode. I can find it for purchase online but because it's not very common it costs about 10 times more than potential alternatives. Also the 1N3880 has D0-203AA (stud) casing and ideally I'd like one with a much smaller profile.

IN3880 characteristics: 6A forward current (max), 100V reverse voltage (max), 1.4V forward voltage (max), 150-300ns reverse recovery time (max).

Which factors are most important when choosing an alternative?

 

IN3880 characteristics: 6A forward current (max), 100V reverse voltage (max), 1.4V forward voltage (max), 150-300ns reverse recovery time (max).

Pretty much those. To find alternates, try a parametric search at Mouser, Digikey, Farnell, Newark etc. Fairchild, ON semiconductor, International Rectifier etc. would be good manufacturers to check out.
The attached has good info from Fairchild about Fast Recovery Diodes.
Good luck.

 

IN3880 characteristics: 6A forward current (max), 100V reverse voltage (max), 1.4V forward voltage (max), 150-300ns reverse recovery time (max).

Which factors are most important when choosing an alternative?

All of them. Here's the first one I looked at.

 

Thanks, I've been looking at them for the past hour or so, I just wondered if there were any values I could prioritise over others. Obviously I wouldn't pick one that went below the values the circuit would be operating at but as it's a fairly low voltage and ampere circuit that doesn't seem to be much of an issue.

Would you say matching the recovery time is the most important factor? Most of them have recovery times far quicker than that of the 1N3880, would this be an issue?

 

http://www.newark.com/multicomp/mbrf20200c/schottky-diode-20a-200v-to-220/dp/17T4210

On sale at $0.15

 

Reverse recovery time and forward voltage drop will affect regulator efficiency. Faster is usually better. For a lower forward voltage, you can consider schottky diodes because you don't need a large reverse voltage rating.

 

I would use a Schottky type, as dl324 mentioned.
They are all very fast (which is good) and have a lower forward voltage so are more efficient and require less heat sinking.

 

We used these with stepper motor drivers. Very robust

http://www.onsemi.com/PowerSolutions/product.do?id=MUR620CT
http://www.onsemi.com/pub_link/Collateral/MUR620CT-D.PDF