Backordered @ Mouser & Digikey. Now what?

I was trying to order some N and P mosfets, part #s

FQP47P06 ← P channels, instock at mouser
FQP50N06L ← N channels, back ordered at both mouser and digi until at least december.

These parts were/are for a large H bridge. After comparing prices (even if they were in stock) I realized I would save only about $25 over ordering an assembled H-Bridge capable of my needs from dimensionengineering.com. (once you factor in the other components.)

So I ordered an H-Bridge from them. Still, this seems to happen to me CONSTANTLY, and as a mostly newb, I have a really hard time telling what replacement parts might work instead, if the sites dont auto suggest for me.

For example, for the P mosfets, the ones that I want have
Input Capacitance (Ciss) @ Vds = 3600pf @ 25V

I found some that had all other specs exactly the same, but this spec was 1900pf @ 25v.

At just barely over half the input capacitance, I wasn’t sure if it would work, and I have no desire to spend $50 on mosfets that I will have no use for.

Are there other places to order from and/or are there general rules for comparing a non stocked part with a stocked part, when the specs are different?

IE could I have used the replacement mosfet I found if it was 4,500pf @ 25v?

Id have to start a new topic constantly to see if things are going to be interchangeable if there are not basic guidelines. IE (Higher is OK lower is not)

Thanks very much.

At just barely over half the input capacitance, I wasn't sure if it would work,

I think that for mosfets, lower input capacitance is better. You want to be able to charge/discharge the capacitance between full on and off states without spending much time in the middle (where the mosfet would have a higher Rdson and higher (possibly fatal) power dissipation)

If you have very specific design requirements for MOSFETs (based on your capacitance concerns), then you need to purchase ones that meet the specs. You seem to be new to h-bridges, so asking around for info might be best before purchase. You don't mention what you need an h-bridge for, but the below kit may meet your needs at a reasonable price. You can add extra MOSFETS as needed for high current applications.

http://secure.oatleyelectronics.com//product_info.php?cPath=94&products_id=206&osCsid=30093449b694ae247d94c2bcce5d0560

Wow, that seems like exactly what I needed, but at about 1/3 of the price, DOH! I need the H-bridge for a large R/C bot. Here is what I ended up getting (much more expensive!) http://dimensionengineering.com/Sabertooth2X25.htm

It does have 2 very nice heat sinks built in,but other than that, I can't figure out why it cost 3x as much? It does have 600/1200 watt capabilities instead of 500/1000 like the one posted, but that doesnt really justify the price difference. May have to use the link you provided for those 500w motors!

I am VERY new to assembling full modules, so I just go off plans I find on the net to get more hands on experience.

I can't figure out why it cost 3x as much?

Well, to start with, it controls twice as many motors...

Well, to start with, it controls twice as many motors...

Can't believe there isn't a 'headshot' smiley here, I deserve it ;D

Im happy with the one I got then, I need two motors for tank steering, and the design looks like it will be very easy to cool thanks to those side mounted sinks.

Also, it leaves more room for my death rays and/or doomsday device ;)

It does have 600/1200 watt capabilities instead of 500/1000 like the one posted, but that doesnt really justify the price difference. May have to use the link you provided for those 500w motors!

Add another $20 worth of MOSFETS, some additional wire and upgrade it to 2000 watts.

Add another $20 worth of MOSFETS, some additional wire and upgrade it to 2000 watts.

That would be awesome, but I would have very little idea where to start. Im working on some entry level electronics projects books right now, and I have lots of hands on experience as far as modifying (via instructions) circuit boards, but I am but a babe in the eyes of circuit design. Do you have any links or book suggestions that contain pertinent info on this?