# Are there any generic “how to use this part” guides for basic discretes?

Coming from a programming background, I'm used to user guides telling me how to use something, rather than how it's implemented. In the world of electronics, when it comes to discretes like, say, a MOSFET, all I can usually find is inventor, history, an overview of the theory and some implementation details.

It's quite hard to find answers to basic questions, like "does a fully turned-on MOSFET conduct more current from source to drain or from drain to source?"

Am I just looking in the wrong places? Or is the best thing to do actually understand the underlying implementation details so that I can deduce the answer from that? It always feels like a bit of an overkill trying to learn how to make MOSFETs when all I want is find out how to use them in a most conventional way.

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For those who speak german: elektronik-kompendium.de –  starblue Apr 11 '11 at 20:29
I also come from a programming background and have exactly this problem: electronics.stackexchange.com/questions/5336/… –  Robert Atkins Apr 12 '11 at 7:35

I don't think there is any such guide. At least if there is one, it will be limited to a few basic uses of the device.

The difference is that if you are using, e.g., a programming library, all you really need to understand is the API. The library is designed to do a few well-constrained things.

Now, a component like a transistor is also designed to do a single thing: a bipolar transistor controls the output (Collector) current by varying the base current. However, that single "feature" has huge amounts of leverage and hides a lot of complexity.

The same transistor can act like a switch: give it plenty of base current and it will saturate and conduct a lot of current.

It's a proportional valve: give it varying, small amounts of base current, and you will get a varying, larger amount of current conducted at collector-emitter.

It's a temperature sensor: give it a small, fixed amount of base current and the voltage from base-emitter will vary depending on the temperature. As a result, the current at the collector-emitter junction will also vary according to temperature.

My point is that the only useful "user guide" to a transistor requires knowing its fundamental properties. You may not need to remember the complete Ebers-Moll model, but you do need to understand the fundamental properties if you're going to use the device to its fullest.

Failing that, if you have a specific question, just ask. Lots of smart people here: someone will be able to help you.

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Very well said! I suspected as much, although to be fair I wouldn't mind a good guide that's limited to only basic uses. –  romkyns Apr 14 '11 at 16:07