Author Topic: TO-247 Isolation Jacket??  (Read 328 times)

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Offline ricko_uk

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TO-247 Isolation Jacket??
« on: October 25, 2020, 11:46:04 pm »
Hi,
I have a MOSFET in a TO-247 package that, due to volume constraints, is bent 90 degrees down onto the PCB. I can only bend it in the direction where the thermal pad (which is also the MOSFET drain) is above the pins of other PTH components from the opposite side of the PCB. Because the pad has a 275Vac it needs to be raised above the board of at least 3.5mm. But there is not enough space inside the tight enclosure.

Two questions:
1) are there any TO-247 insolation jackets for this purpose? i.e. that I can slide over the entire TO-247 or at least at the back to electrically isolate AND/OR provide and guarantee the required gap?

2) I have been looking at various TO-247 MOSFETS without a conductive/connected thermal pad but couldn't find any in the datasheets I looked at. Is there a way to find such MOSFETs without a conductive thermal pad? If so how?

The MOSFET I am using is 550V 13-15A...: http://www.farnell.com/datasheets/2148558.pdf

Thank you :)
 

Offline jbb

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Re: TO-247 Isolation Jacket??
« Reply #1 on: October 26, 2020, 12:09:39 am »
Err, I don’t know part numbers, but you can get silicone socks. These would fall under thermal management / heat sink pads in the catalogs.

You’d probably need to fasten it somehow. I would suggest that your TO-247 needs to be mechanically fastened down anyway so it doesn’t shake about. Solder joints will fatigue and crack if you have a mass (TO-247 body) and spring (legs) attached. I think you can find compression clips, which just squeeze down on the outside of the sock, for this.

You know, this sounds aggravating. Are you sure you can’t find a surface mount solution?
 

Offline ricko_uk

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Re: TO-247 Isolation Jacket??
« Reply #2 on: October 26, 2020, 12:35:56 am »
Thank you jbb ! :)

it would be ideal, but cannot find a 500V 13-15A SMD. I think it has to do with thermal dissipation.
 

Offline radar_macgyver

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Re: TO-247 Isolation Jacket??
« Reply #3 on: October 26, 2020, 05:58:40 am »
I have seen such sleeves for TO-220 devices, like these, they may not be wide enough for a TO-247.

DK lists 308 SMD MOSFETs with >= 500V Vds and >= 13A Idd. For example, the STB45N65M5, which is also available in TO-220, with an isolated body. There's also the much cheaper IPD60R180P7SAUMA1.
 

Offline jonpaul

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Re: TO-247 Isolation Jacket??
« Reply #4 on: October 26, 2020, 09:03:51 am »
Helpful to have a photo of the heatsink, PCB and transistor to understand what you need.

Jon
Jon Paul
 

Offline mag_therm

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Re: TO-247 Isolation Jacket??
« Reply #5 on: October 26, 2020, 05:26:30 pm »
Does that have a creepage (surface tracking) requirement as well?
 IEC-60950-1  etc
 


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