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Or is the packaging just different?

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If it is the same base part number, same power, different packaging. Heck, its frequently the same die.

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    \$\begingroup\$ ICs almost certainly have the same die. Those things are expensive, and it would be senseless to design a new one for a different package. \$\endgroup\$ – Kevin Vermeer Mar 7 '11 at 21:38
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No.

But through hole components can often handle more power than surface-mount components. Because they are larger, they have lower junction-to-ambient thermal resistance.

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    \$\begingroup\$ Woah! I was going to say the opposite. Surface mount components can be connected to large areas of copper on the PCB through a die pad, and thus have lower effective Θja. \$\endgroup\$ – Kevin Vermeer Mar 7 '11 at 22:35
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    \$\begingroup\$ @reemrevnivek - And through-hole components can be mounted to a heatsink. External heatsinking does not change the fact that, without heatsinking, through-hole components can generally handle more power. \$\endgroup\$ – Connor Wolf Mar 7 '11 at 23:02
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    \$\begingroup\$ It's not a hard and fast rule, I've just noticed when reading the datasheet of a part available in both packages, the SMT package will have a lower power rating. \$\endgroup\$ – markrages Mar 8 '11 at 0:17
  • \$\begingroup\$ SMD components can be mounted to a heatsink as well. \$\endgroup\$ – Kevin Vermeer Mar 8 '11 at 4:43
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    \$\begingroup\$ Assuming no heatsink, Through hole is regularly higher-power. Heatsinks are an additional option, and not mentioned anywhere in the question. \$\endgroup\$ – Connor Wolf Mar 8 '11 at 8:27
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What they said. Plus:

"Power used' is very largely a matter of the circuit parameters rather than the components themselves. Something like a resistor will use exactly the same power for a given task regardless of it's packaging as the designer has complete control over power dissipation. Differences that do occur are liable to be due to secondary effects.

For example:

1) More modern ICs for switch mode power supplies, operating at higher frequencies with potentially improved efficiency may be available only in SM packages, so their "lower power' may not be available in an older package. This is thus a factor of availability rather than inherent difference due to package.

2) A MOSFET may operate more efficiently at lower junction temperature due to eg increasing Rdson with temperature. Identical die with different packaging will then produce different results based on thermal resistance from Junction to air. This is made up of Rth_junction_case + Rth_case_sink + Rth_sink_air. Depending on implementation and power level (not to mention phase of the moon) the result may go either way. At high power levels a larger through hole case may have a higher Rth_junction_case, but have better access to gross ambient heat sinking. At power levels below 1 Watt the ease of access to PCB thermal sinking for SM part may encourage a lower temperature design so higher efficiency so lower power overall.

As others have noted, 3rd order effects such as lead lengths, perhaps reduced capacitance and similar will have some effect, but usually minimal

Summary: Overall neither SM or through hole have an explicit power difference BUT factors specific to each implementation may make a difference either way on a case by case basis.

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Generally no difference between the same part in different packages, the more important difference is that 'better' parts tend to only be available in SMD as that is where the market for efficient parts has gone. For example high-efficiency DC-DC converters often operate in the MHz range, which isn't practical in TH due to lead inductance.

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Ever so slightly, yes - because the leads are shorter and there is less resistance in those tiny leads which leads to less wasted in these leads ;). (It may well be only a few milliohms and a few milliwatts dissipated (if that), but...)

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  • \$\begingroup\$ This is probably more of a problem in RF and high frequency components, where the switching speed of the signal causes losses due to the inductance and capacitance of the leads. More energy is required to maintain signal integrity. \$\endgroup\$ – Kevin Vermeer Mar 8 '11 at 4:39
  • \$\begingroup\$ @reemrevnivek, I wasn't being serious, if you've got a 50mohm MOSFET, what's <1 mohm of wire gonna do? \$\endgroup\$ – Thomas O Mar 8 '11 at 10:14
  • \$\begingroup\$ I understand that you weren't being completely serious on the resistance front, but there are plenty of situations where through-hole and SMD packages have significantly different inductance and/or capacitance. \$\endgroup\$ – Kevin Vermeer Mar 8 '11 at 13:10

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