Good day,

I am doing comparison of two MOSFETs on the basis of package information & dimensions given in datasheet by both manufacturers.Honestly, i don't know much about this design aspect, so if anyone could help me regarding that.
The background of this activity is that we want to change this MOSFET B with MOSFET A without doing any changing in PCB layout and I need to confirm if its possible using the details provided on datasheet. I have attached Information about package and dimensions of both MOSFETs in attachment.
Thanks in advance

 

If you are planning to mount these to a heat sink, you likely need the same package and pinout.

If you are not using a heat sink, the pinouts must be the same and the outline must be compatible with the space you have allowed on the PCB.

You also have to make sure both meet the thermal dissipation requirements. For example, a TO220 might be replaceable by a TO92 in pinout, but it will not be able to dissipate the same power.

 

Do you only care about mechanical compatibility or do you also need electrical compatibility?
If it is the later, what are the specifications of both transistors?

 

Do you only care about mechanical compatibility or do you also need electrical compatibility?
If it is the later, what are the specifications of both transistors?

I have already done feasibility study in electrical domain and both MOSFETs are electrically compatible. attached is the datasheets of both MOSFETs for your reference. will wait for your valuable comment on my question.
Thanks

 

If you are planning to mount these to a heat sink, you likely need the same package and pinout.

If you are not using a heat sink, the pinouts must be the same and the outline must be compatible with the space you have allowed on the PCB.

You also have to make sure both meet the thermal dissipation requirements. For example, a TO220 might be replaceable by a TO92 in pinout, but it will not be able to dissipate the same power.

yes, FET will be mounted on heat sink. we are using TO247 package which is same for both MOSFETs. I am not sure about Pinout comparison of both MOSFETs. If you could kindly comment on that. attached are the datasheets of both MOSFETs.
Thanks

 

yes, FET will be mounted on heat sink. we are using TO247 package which is same for both MOSFETs. I am not sure about Pinout comparison of both MOSFETs. If you could kindly comment on that. attached are the datasheets of both MOSFETs.
Thanks

The pinouts are the same.

 

The pinouts are the same.

Thanks for your valuable comment. Could you also please comment if the dimensions of both MOSFETs specified in datasheet are compatible without changing layout?
Thanks

 

For further doing of this you just need to look at the mechanical drawings of both packages in their data sheets.

 

For further doing of this you just need to look at the mechanical drawings of both packages in their data sheets.

Thanks for your comment.
I have already studied the mechanical drawings of both packages provided on datasheets but I am unable to conclude if there is any difference or not. Could you please have a look at datasheets and give your valuable advise? I have attached both datasheets for your reference.
Thanks

 

(Ok, we have enough copies of your datasheets :- )

 

yes, FET will be mounted on heat sink. we are using TO247 package which is same for both MOSFETs. I am not sure about Pinout comparison of both MOSFETs. If you could kindly comment on that. attached are the datasheets of both MOSFETs.
Thanks

Looks like the TO247 is 0.225 inches longer from lead holes in the PC board to the top edge near the hole. That's significant, but you really have to check the board itself to find out if you have the extra room. I checked the mounting hole distances but I didnt check anything else because the length and hole position difference was so significant.

When you want to figure this out, you add measurements that are in the same direction, and subtract any that are in the opposite direction. This is how you calculate the distance from the PC board lead holes to the mounting hole in the part, assuming you are using a screw mount not a clamp type mount. The center to center distance for that is 0.122 inches more for the TO247 and that is significant also. The center to center hole distance is very important if you intend to use a screw mount, but shouldnt matter if you use a clamp type mount. If you do intend to use a screw mount you'd have to drill the hole out more, which could interfere with the traces on the other side of the board.
If you have some extra height, you can make up an adapter but that's not that easy either.
Note the distances for both are slightly greater depending on how you bend the leads.
A vertical mounting scheme would mean one is higher than the other and mounting holes still different too.

 

(Ok, we have enough copies of your datasheets :- )

Ok than could you please give your valuable feedback on my post.
Thanks

 

Looks like the TO247 is 0.225 inches longer from lead holes in the PC board to the top edge near the hole. That's significant, but you really have to check the board itself to find out if you have the extra room. I checked the mounting hole distances but I didnt check anything else because the length and hole position difference was so significant.

When you want to figure this out, you add measurements that are in the same direction, and subtract any that are in the opposite direction. This is how you calculate the distance from the PC board lead holes to the mounting hole in the part, assuming you are using a screw mount not a clamp type mount. The center to center distance for that is 0.122 inches more for the TO247 and that is significant also. The center to center hole distance is very important if you intend to use a screw mount, but shouldnt matter if you use a clamp type mount. If you do intend to use a screw mount you'd have to drill the hole out more, which could interfere with the traces on the other side of the board.
If you have some extra height, you can make up an adapter but that's not that easy either.
Note the distances for both are slightly greater depending on how you bend the leads.
A vertical mounting scheme would mean one is higher than the other and mounting holes still different too.

Thank you for your valuable comment.
Could you please confirm that if you are comparing TO247 packages of both MOFETs, from IXYS Liitlefuse and from Infenion one. Also this 0.225 inches difference is which parameter specified on datasheet? same for centre to centre distance as well that it is which particular parameter as per datasheet. I am sorry for this question but I am unable to understand that.
Thanks

 

If you do not understand the information in the data sheets and the very clear explanation that MrAl gave you, maybe you should ask someone more qualified than you to do the task to ensure its success.