I'm designing a SMPS for a fairly high-power application (2kW, 50A). In looking at the available components, sometimes almost the exact same components are available in surface-mount and through hole versions, for example: FDB035N10A in D2PAK and FDB036N10A in TO-220. The specs are very similar, except the surface-mount component has a higher power dissipation rating.

Is it preferred to use surface mount components in this case? What is more common or industry-standard? What are some of the pros and cons?

  • \$\begingroup\$ This question boils down to "should I design with SM components". It has nothing specifically to do with switchers. \$\endgroup\$ – Andy aka Sep 14 '15 at 8:59
  • \$\begingroup\$ @Andyaka: Perhaps "should I design with SM for high power" :) Or even better, "is there any reason not to", since the general benefits of SM are well known. \$\endgroup\$ – Alex I Sep 14 '15 at 9:00
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    \$\begingroup\$ SMD FETs generally have nicer characteristics, less ringing \$\endgroup\$ – RYS Sep 14 '15 at 9:23
  • \$\begingroup\$ If you believe the data sheets for leaded components then there is no reason to reject them because they are SMD (other than naivety). \$\endgroup\$ – Andy aka Sep 14 '15 at 9:55

Yes, you can use SMD for high power.

The ease of automated assembly is a compelling advantage in most western countries. Here are some things that will help:

  • You can get aluminium-backed PCBs that can have SMD power devices on one side, and the aluminium side of the PCB goes flat on a heatsink. The thermal impedence isn't as good as a mica washer but it's workable.
  • The lower purchase cost and the much lower assembly cost of power devices means that you can use more of them, which means you can spread the heat.
  • Doing something about switching losses is very important because most orthodox current mode PWM has more switching loss than conduction loss when being operated at normal frequencies.
  • Generally your SMD PCB will have less parasitic inductance than a thru hole PCB of the same circuit. This will mean cleaner waveforms especially at high currents and can help reduce radiated EMC.
  • Some of the better parts are easier to get in SMD.

if the SMD parts support a use with a suitable heatsink there's no reason not to choose them.


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