is there any advantage of using a TO-220 or a D2PAK MOSFET over the other?

I'm currnetly using 2 D2PAK MOSFETs in a motor control board for a 30A motor. I ran the motor pulsed at 150Hz, 50% duty cycle for about 8 minutes, and the MOSFETs got so hot that the solder started flowing.

on the opposite side of the D2PAKs, on the other side of the board, I used thermal epoxy to stick pieces of aluminum as a heatsink and mounted that to a metal box, which serves as an enclosure for the entire project and the box was absorbing the heat pretty well. I just have a feeling that the area right behind the D2PAK was getting way too hot and melting the solder.

Is it better to use the TO-220 package and mount some sort of large heatsink in the air? I would ultimately like to mount the backs of the TO-220 to the box itself as a heatsink, but the flange of the TO-220 is drain and not ground.

any pointers or tips?

 

Get a TO-220 insulating mount - http://search.digikey.com/scripts/DkSearch/dksus.dll?Detail&name=4724K-ND

 

Can't speak from firsthand experience with these surface mount heatsinks but they would appear to be a viable solution.

hgmjr

 

These are pretty good for high power circuits.
http://www.asc-i.com/products_metal.htm

As far as TO-220 vs D2PAK goes, they are similar when not heatsinked and the D2PAK is mounted i.a.w the datasheet. But it is easier to put a large heatsink on a TO-220 part though.

 

Which D2PAK MOSFETs are you using?

Can you post a schematic diagram and board layout?

 

There are also surface mount heatsinks that can be used for DPAK and D2PAK parts.

http://www.r-theta.com/products_boardlevel.asp

It may not be enough for this purpose since you say you are melting the solder on these parts.

 

Have you calculated how much power you are dissipating and the thermal resistance of the
package? It is hard to determine the best solution without this calculation.

D2PAK's use the copper pad under the tab as the heatsink. You need to determine
the thickness and area of this pad using the thermal resistance specification in the datasheet. This can consume a lot of board area and require a more expensive PCB
process to get thicker copper.

For TO-220's sometimes I use a PCB mount heatsink. Other times I hang the device off the PCB and mount them to an external heatsink. You can get insulating mounts. Some
devices used to be made with an insulated tab. You need to watch the thermal resistance.

Here are some thermal resistance notes ---

To determine the temperature rise you need to calculate the junction
to ambient thermal resistance (Tja) ---

Tja = Tjc + Tcs + Tsa all the dimensions are DegC/W

Tjc thermal resistance between the IC junction and IC case. This is
from the IC datasheet.

Tcs thermal resistance between the IC case and your heatsink. This
should also be in the IC datasheet. Usually you place a thermal
compound between the IC case and the heat sink to decrease the
thermal resistance. The decrease occurs because the thermal
compound fills the air gaps between the two surfaces and conducts
heat better than the air.

Tsa thermal resistance between the heatsink and ambient air. This is
in the heatsink datasheet. Most heatsink datasheets specify Tsa
with and without airflow. You can determine if you need a fan by
reviewing this number.

For a single heatsource the junction temperature would be

Tj = Tja * P + Tamb (DegC)

where P is the power dissipated in the IC and Ta is the ambient
temperature. For a MOSFET P = rds(on) * Id (NB: use the rds(on)
value at the actually operating temperature). For BJT
P = Vce(sat) * Ic (NB: use the Vce(sat) value at the operating
temperature).

The maximum juction temperature is listed in the datasheet (usually
in the "Absolute Maximum" section). I would not run the device at
a temperature greater than 80% of the the absolute maximum rating.

Unless you have very short on times PWM is not going to help
much with power dissipation. To see how much look at the transient
thermal response graphs in the datasheet.

(* jcl *)