I'm investigating SMPS circuits and I'm trying to design my own.

In my design, I have a 300mOhm current sense resistor and its power rating must be minimum 177mW so I need a 500mW resistor. I have chosen a 2512 SMD package 1W resistor for it.

When I investigated other SMPS circuits that have same specifications (same output wattage & voltage) I noticed that they have through hole type resistors. Is there a reason for it or any reason to avoid using SMD type current sense resistors?

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    \$\begingroup\$ To be fair, all the other components are through hole. So your comparision is not valid. \$\endgroup\$ Jan 3 '21 at 19:06
  • \$\begingroup\$ Not all components are th. Pcbs have bottom side and there are a lots of smd components (pwm controller ic. Etc.) \$\endgroup\$ Jan 3 '21 at 19:51
  • \$\begingroup\$ PCB real estate would be one. \$\endgroup\$
    – winny
    Jan 3 '21 at 21:00
  • \$\begingroup\$ OK, there are surface mount components, but this probably has more to do with parts not available in through hole packages. \$\endgroup\$ Feb 26 '21 at 6:34

One reason is probably that the surge power capability of larger resistors, especially wire-wound ones, is much better than surface mount resistors. It mainly relates to the thermal capacity of the resistor - large is better in general.

In this application a surge may occur is the supply is shorted, before the current limiting comes into effect.

Your choice of a 2512 2W resistor does seem to be a good one though with a good pulse load capability.

https://www.bourns.com/docs/product-datasheets/crm-a.pdf?sfvrsn=353a74f6_13 Bourns Thick film resistor 11 things you need to know about resistors in pulse load applications


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