How can I know how much current a transistor or other component can handle?

Before frying? Is there some sort of rating?

I’ve gotten into building things from schematics and project kits and so on, but I’ve never been clear on how much each component can handle. I’d like to start messing around more and start doing stuff from scratch more, but I don’t know how much leeway I have with stuff before it’s going to get fried or an LED is going to burn out.

Is this a rating somewhere? Is it common knowledge? Where can I find this out?

There are usually data sheets available from the supplier or manufacturer of electronic components specifying voltages, currents and just about anything anyone would need to know.

I strongly suspect that if you have the component designation you can look it up on the net.

You mean you don’t know? :smiley:

Calling Q.E.D. He’ll know…

There are three ratings (generally): Maximum current, maximum voltage, maximum power dissipation. They are all noted on the data sheet. For things like LEDs, you can exceed the maximum instantaneous power dissipation as long as the the continuous power dissipation is under the max (in other words, you can drive them with high-current pulses).

For transistors, a book like Towers’ International Transistor Selector can’t be beat. It gives all the useful parameters for thousands of different transistors, plus other stuff like pin configurations and suggested equivalents if you can’t find the transistor you want.

Basically, you will need to find the name of the component. If it’s a circuit you’re building from someone else’s design, you should find the component’s name on the schematics. If you’re looking at a physical component, the name should be printed on the component itself.

Then, look up the component’s data sheet. Most (if not all) data sheets are available on the web. Just Google <your component> “data sheet”.

When looking at the data sheet, be careful not to confuse the “Absolute Maximum Ratings” with the “Electrical Characteristics”. The AMR, like the name suggests, are absolute maximum, above which the component is likely to be fried. Do not design according to these values as the working point. The EC give you the data you need for the design. In these you’ll find either Maximum or Minimum rating for each line, and sometimes an additional “Typical” rating. The rating given (Min/Max) is the worst case. You should design your circuit to work below these ratings.

BTW, some components are “generic” (resistors, capacitors, and the like). For these, you’ll need to recognize the component class. I don’t know of a way other than experience, or someone pointing these to you.