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Update Cancel. Tags Engineering. Sometimes you get both, sometimes you only get one or the other. For all IC packages, pin numbers increase sequentially as you move counter-clockwise away from pin 1.
These ICs will usually have a dot near pin 1. Not all capacitors are polarized, but when they are, it's very important not to mix their polarity up. You can stick those in either way. Through-hole and SMD 0. These are NOT polarized. Electrolytic caps they've got electrolytes , which look like little tin cans, are polarized. They might also have a longer positive leg. Applying a negative voltage for an extended period to an electrolytic capacitor results in a briefly exciting, but catastrophic, failure.
They'll make a pop , and the top of the cap will either swell or burst open. From then on the cap will be as good as dead, acting like a short circuit. Getting polarity right in your circuit all starts and ends with getting the power supply connected correctly. Whether you're project's getting power from a wall-wart or a LiPo battery , it's critical to make sure you don't accidently connect them backwards and apply - 9V or - 4.
Anyone that's ever replaced batteries knows how to find their polarity. Other times it might be red wire for positive and a black wire for negative. An assortment of batteries. Each has some way to represent positive or negative terminals. Power supplies usually have a standardized connector , which should usually have polarity itself. Other connectors, like a JST , are keyed so you just can't connect them backwards.
For extra protection against reversing power supply polarity, you can add reverse polarity protection using a diode, or a MOSFET. These traditionally three-terminal, polarized components are lumped together because they share similar package types.
To find which pin is which, look for the flat edge on the TO package or the metal heatsink on the TO, and match that up to the pin-out in the datasheet. Above, a 2N transistor in a TO package, note the curved and straight edges. This is just the tip of the polarized-component iceberg. Even non-polarized components, like resistors , can come in polarized packages. A resistor pack -- a grouping of five-or-so pre-arranged resistors -- is one such example.
A polarized resistor pack. The dot represents the first, common pin. Fortunately, every polarized component should have some way to inform you which pin is which. Be sure to always read the datasheets , and check the case for dots or other markers. Now that you know what polarity is, and how to identify it, why not check out some of these related tutorials:. See our Engineering Essentials page for a full list of cornerstone topics surrounding electrical engineering.
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