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Choosing components (Transistors, Diodes ect.)

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Triode

Active Member
Could some of you post guides, or your own information, as to what factors go into selecting the correct component for a job in general? I think resistors are fairly well covered, but transistors and diodes can be more confusing, and theres a bit more to know about inductors and capacitors than whats obvious.

I've been doing a lot of pre drawn projects and tutorials, and I'm getting a sense of whats needed, but unfortunatly most of the guides say things like "use a P-Channel 350V 25Ohm Mosfet (part number) here" they don't often explain why that is the component for the job.

Oddly its easier to find guides that assume you know nothing at all, but once you've covered what a collector, base, and emmiter are they dont teach you much more. I'm looking for something that tells me some equations and guidelines, more at the level you would give a non-electrical engineer who needed to work with some electronics.
 

Triode

Active Member
Cool, those should be helpfull. I've been using some paper text books, but those are kinda expensive, and the library doesnt have a lot.
 

Willbe

New Member
Safe Operating Area is a good term to search, along with derating and thermal resistance.
 

Triode

Active Member
Thanks! I didn't know about that, and it adds a lot of clairity, I've seen those graphs on datasheets but I didn't know how to read them before.
 

Thunderchild

New Member
start by seeing what you can actually get hold of and choose from whats available the component that best suits your needs leaving as large safety margines as you can
 

Triode

Active Member
That is true, and I apriciate the advice. I was looking for the technical information needed to know where you are withen the margines of safety. But it is important to know that you need to select practical components and that its a good idea to have some factor of safety in your selection.
 

Thunderchild

New Member
well I would think 50-100 % margin is a good idea for diodes and transistors, it all depends really, I examined a fan seed controller at work a littlr while ago to find that despite we are using 5 amp motors max and that the skotky diodes were "only" 10 A anyhow the power mosfet is a 120 A one, but if it comes cheap enough and means that at 2-5 A you don't even need a heatsink then why not have the 2400 % margin, it all comes down to the application and what you want to do make sure you meet you minimum requirements + margin and then get as best you can for the price, you can use a 5 A fet @ 3 A with a heatsink or a 120 A FET without one, if you have a space constraint or the difference between the 120 A and the 5 A is less than the price and hassle of a heatsink then you will go for the 120 A one. in theory both are good but in oractice one has advantages over the other.
 
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