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Why are SMD components so much smaller than their THT versions?

Nabors

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I've been doing my prototyping a high current circuit with 25ish amps using tht components. I recently ordered some smd versions of the same components to see the size they would be for a circuit board. I am stunned at how much smaller the smd version of a 200A mosfet is. I was able to solder some leads into it just because I couldnt believe it would handle the current the same way as the much larger THT component. To my surprise, after maybe an hour or so of keeping the large LED on, it didnt gain any more heat than the through hole mosfet.

I'm just struggling to understand how something a mere fraction of the size can handle it?
 

barry

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The die is the EXACT SAME SIZE for through-hole or SMT devices. The TH parts are bigger in order to acommodate the larger lead frame. You'll notice that SMT leads are much smaller than TH leads...
 

asdf44

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Well don't be fooled by mosfet ratings.

When it comes to heat dissipation size matters. Even with the same "200A" die you'll be able to push more power from a bigger package.

You need to carefully follow the junction-to-board or junction-to-ambient thermal impedance numbers to calculate actual current handling. You can only get about 1-2 watts from an SMT part in typical ambient conditions. To get more you need large areas of copper, heatsinks, airflow etc.

Run the numbers and you'll find even 20A is hard to get from your "200A" fet.
 

schmitt trigger

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What ASDF44 said.

If you attach the datasheets for the Mosfet you employed, we can help you with the thermal calculations.

Even if you don’t require the help, for the benefit of other future readers, it would be sensational if you did so.
 

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