Simple question and not really sure where to put this in the forum so here it is. Im designing a new SMT board based on older through-hole designs for a micro to ULN2003 to 5v unipolar stepper. The 2003 is responsible for sinking the motor current and is set up in such a fashion that 2 i/o lines from the micro can step the motor. In my older designs I had been using some blue NTE 1 watt 5ohm through hole resistors for current limiting to the stepper. Maybe a super cool Eagle3D image might help…
That big resistor has to go! Problem is the 1W version gets a little hot as it is. I tried a ceramic 5ohm 5watt version and that ran cold, but that was especially huge. I would like to go all SMT if I can but Im new to SMT designs and the Mouser catalog is just sitting in front me taunting me. All I need are some of your suggestions for 5ohms in 2 or 3 (or more?) watts in SMT?
Take a look! Actually, Digikey has a much better system if you’re just digging. They do have up to 5W in SMT 5 ohm packages, but it’ll be almost $2 a chip. The other problem is size. I found a SMT wirewound 1% 5 ohm 2 watt there in a 4527 package (WSC45275R000FEA). I don’t know if something that big would even have a chance of fitting on your board. I’m thinking not.
I have not been working with smt long, but there are not many resistors that big in smt(to my knowledge). That is a huge amount of wattage for a smt resistor.
I know you would like it smaller, is it that important?
The Eagle parts library should have package information on that resistor. I’ve seen them before but don’t know what they are called off hand.
To get the power handling that you want, you can always parallel a number of resistors to share the load. Just make sure their equivalent resistance matches what your circuit needs.
