Questions You Should Know about Custom Schottky diode suppliers Company

Even better would be if someone could explain what I would be looking for as far as data sheet specs go so I can learn how to pick one myself in the future. I have a basic knowledge of electronics but I get lost when I read about forward voltage vs reverse voltage, leaked current vs rectified, recovery time, etc and how it would all relate to this and future projects I am working on.

First you think through what the various properties are. Sometimes it helps to write it out on paper (or whatever), especially when it's a new field for you or a complex problem, so let's do that:

• Forward voltage drop: The voltage loss across the diode when it's conducting. Varies with current. The reason people like Schottky diodes is that this type has low forward voltage drops. An "ideal" diode would have zero forward voltage drop.
• Reverse voltage: the maximum voltage you can apply to the diode in reverse polarity before it lets out the magic smoke. 
• Leakage current: when a diode is reverse biased, some current leaks through anyway. The smaller, the better.
• Rectified current: how much current the diode can pass comfortably before the manufacturer is no longer prepared to guarantee the magic smoke will stay in the part.
• Recovery time: how fast the transition from reverse to forward biased can be.

Then you think about what's important in your application. For power-ORing diodes, recovery time is usually totally insignificant. Reverse current is also usually not very important. Reverse voltage needs to be above the value of the highest power supply in the system (i.e., if you're ORing 12V and 5V, all the diodes better be rated 12V or higher!). You also need a bit of headroom; it's never good to run parts at 100% of their rating if it can be avoided. Your rectified current, as you've identified, should be 500mA minimum. (I might choose the next size up, 1A, Just In Case&#;. Or I might not, if I'm size-constrained on the layout or it's a non-critical part.) And then you can just pick the part with the lowest forward voltage drop that meets your other criteria of price, package size, availability, &c.

(Also consider what else you could use this part for; often it is better to buy two identical parts, even if they're individually a bit more expensive or somewhat overspecified, than managing two separate part inventories for different parts in different circuits. BOM line item reduction makes everyone happy!)

I adore manufacturer catalogs that list all their parts and relevant specs, because it makes this game a lot easier. NXP has a great MOSFET and diode catalog,

Sometimes if I need something a little more exotic, availability will be more limited. (That is not the case with bog-standard diodes.) In that case I usually start with the distributors' sites and see what they've got first, rather than what's in the catalog and might or might not be actually purchasable.

First you think through what the various properties are. Sometimes it helps to write it out on paper (or whatever), especially when it's a new field for you or a complex problem, so let's do that:Then you think about what's important in your application. For power-ORing diodes, recovery time is usually totally insignificant. Reverse current is also usually not very important. Reverse voltage needs to be above the value of the highest power supply in the system (i.e., if you're ORing 12V and 5V, all the diodes better be rated 12V or higher!). You also need a bit of headroom; it's never good to run parts at 100% of their rating if it can be avoided. Your rectified current, as you've identified, should be 500mA minimum. (I might choose the next size up, 1A, Just In Case&#;. Or I might not, if I'm size-constrained on the layout or it's a non-critical part.) And then you can just pick the part with the lowest forward voltage drop that meets your other criteria of price, package size, availability, &c.(Also consider what else you could use this part for; often it is better to buy two identical parts, even if they're individually a bit more expensive or somewhat overspecified, than managing two separate part inventories for different parts in different circuits. BOM line item reduction makes everyone happy!)I adore manufacturer catalogs that list all their parts and relevant specs, because it makes this game a lot easier. NXP has a great MOSFET and diode catalog, available here , and guess what? I pick NXP diodes a lot more often than other manufacturers'. (HINT FOR MANUFACTURERS: make my life easier and I'll buy your parts!) If you load that up and scroll to around page 36 (PDF page 20 because they paginated it bizarrely), you'll see a whole bunch of candidate parts. Many would probably work for your application. PMEGEJ looks like a decent starting point, but you may prefer to optimize for other things (smaller, higher power, better available, etc.) I usually pick a couple of favorites that look good, then search DigiKey, Mouser, or Octopart and see how available and expensive each is, and then just pick one.Sometimes if I need something a little more exotic, availability will be more limited. (That is not the case with bog-standard diodes.) In that case I usually start with the distributors' sites and see what they've got first, rather than what's in the catalog and might or might not be actually purchasable.

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Most of your questions can be answered "yes", but be careful with Schottky vs. (ultra) fast diodes:

"Can I just buy the higher voltage and current rated Schottky diode and sub them for the lower rated ones?" Should Work.

"Is the main reason for getting the exact match the cost and ability to fit?" Some issues like the diode's capacitance have an influence on switching speed and, as a consequence, switching losses, i.e. heat generated in the diode. Try to find at least a similar device. Also, pay attention to peak values for current spikes and the like. Average current is one thing, peak current and power handling capabilities are another.

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"Do I only need to match package/voltage/current?" This is what designers do when looking for second source parts. In most cases, you will be good to go.

"Are Schottky and fast recovery the same?" Usually, fast recovery is a label for p-intrinsic-n diodes, i.e. Si diodes, that are trimmed towards blocking fast upon being reverse biased. Schottky diodes are, really, always as fast as can be and should not be replaced with slower Si diodes, even when they're labeled "fast". The general rule is: Don't replace Schottky with Si diodes.

"Can I sub an ultra-fast for a fast recovery?" Using an ultra-fast Si diode in place of a fast Si diode should work as far as switching losses go, but the faster switching action might cause worse electro-magnetic emissions.

"And... at the moment I need a Schottky that is in the TO220 package. Can I use two axial leads and just wire the cathodes together?" Diodes in three-pin TO220 packages are really just two diodes. They are, however, very similar. When connected in parallel, they will share the load really well. Different packages are also often a hint towards different peak current/power handling capabilities. And, of course, thermal properties will be different. A TO220 has its own little heat sink even when mounted in free air; axial diodes don't have this nice feature.

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