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I'm pretty new to electronics as a hobby - been picking it up on and off for the past 2 years or so - and there's always one thing i always stumble and doubt myself on, how do i select components?

For example, I am currently looking for triacs to switch mains AC voltages, I originally ordered some T3035H-6T's but cancelled the order after seeing This question where the asker (seemingly trying to accomplish the same goal) has decided to use BT136's, which made me doubt my decision.

I have done the same before when buying Mosfets, and basically any transistor i have ever gone to use, is there are real, tangible difference when selecting components like this? when i look at the datasheets for the respective components i am seeing little difference between the two (obviously this wont apply across the board, but for the pair i have given as examples), does this mean they are basically a pair of components that are freely interchangeable between?

Am i being stupid and reading the datasheets wrong, or are my assumptions correct?

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    \$\begingroup\$ It all depends on how you're using the parts. If you're using a MOSFET as a switch with a maximum applied voltage of 12 V, it doesn't matter whether you use a 25 V or 30 V rated part. But if you use a 6-V rated part you're going to have trouble. Similar thing for every other spec on the datasheet. \$\endgroup\$ – The Photon Apr 26 '16 at 16:30
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    \$\begingroup\$ @ThePhoton Thanks for the input. I think my issue is maybe i think this is more complicated than it actually is, and i'm perhaps intimidated by the range of choices & plethora of data regarding them. \$\endgroup\$ – Trotski94 Apr 26 '16 at 16:34
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    \$\begingroup\$ The thing is, every spec on the datasheet is important to somebody, but very few users really need to look at all of them. But which ones are important to you depend entirely on exactly what circuit you're going to use the part in. \$\endgroup\$ – The Photon Apr 26 '16 at 16:35
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It sounds like you are just lacking a little confidence in your choices, which will come with time as you build experience in your hobby and see electronics working.

The thing is, there are often tons of components that would do the job. The fact that someone else picked a different part for the same task than you could be anything from the serious (there is a minimum required spec that yours doesn't meet) to something practical (the supplier in their country is out of stock of your part) to something more subjective ("I always buy from brand XX, I like their website).

To answer your question, which is essentially, how to select components, I'll give you some pointers that I use and see how it works out for you.

  1. Go to DigiKey's website. There are lots of other good electronics suppliers, but at least for finding components I prefer them for their amazing filtering.
  2. Type in "Triac" into the main search box.
  3. You'll now get different categories of results. I'm pretty sure the category you want (just trying to walk you through an example for now, not find your exact part understand), is the "Triacs" category. :)
  4. This is just user preference, but right off the bat I usually click "In stock" (I don't want to mess with low stock parts, which may be going out of lifespan) and hit Apply Filters.
  5. Then I type "1" into the Quantity box and hit Enter. This will eliminate options like Tape & Reel where the minimum order might be thousands.
  6. Now start filtering the lowered number of choices by your required specs. For example, you may require through-hole or surface mount, based on if your prototyping with protoboard, for example. Or you likely have voltage and current requirements that it must meet. You can CTRL + click or SHIFT + click to select a wide span of things that fit your interest. Click Filter again.
  7. You should now have a more reasonable number of choices of parts left. At this point, if you've really entered in all the specs you care about, the rest shouldn't matter. At that point I usually do the following:
  8. Sort by Quantity Available, descending. This gives me a rough proxy for how popular the part is. Yes, you could miss out on parts that are popular but are just low in stock. This is better than the opposite -- picking a part that is so unpopular that it's never in the thousands. We want popular parts in general because there will be more resources online of others who have used them and just generally more collective knowledge out there. Now take a note of the prices of some of the popular ones.
  9. Now sort by ascending prices. Are some of the cheapest ones also one of those most popular ones? If so, good, you've found your part. If not, get an idea for what makes the prices points jump. You sometimes find there is a feature that others have that you might wish for that you didn't think of. Sometimes with microcontrollers you can literally spend only a few pennies more and get another feature you might need someday, so you may wish to not buy the cheapest necessarily.

I hope this gets you started. The confidence will come with time. Maybe that user will see your project and wish they'd picked your part instead. Remember that if you meet all the important specs for you, then you are good. Some other features are nice-to-have and others are so nice they become needed. ;)

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