IRF3205 share cooling plate question

Thread Starter

LAOADAM

Joined Nov 21, 2018
166
trying to make a 6 way mosfet switch, each mosfet working separately and independent.
Can I use just one piece of cooling plate for all of them? that means all mosfet's Drain hook up..

Thanks
 

jpanhalt

Joined Jan 18, 2008
7,871
trying to make a 6 way mosfet switch, each mosfet working separately and independent.
Can I use just one piece of cooling plate for all of them? that means all mosfet's Drain hook up..

Thanks
Show your schematic. Are you saying a common drain?
 

dendad

Joined Feb 20, 2016
2,986
Mount the FETs to the heatsink with insulation kits.
upload_2019-7-23_8-43-56.jpeg

There is plenty of info about it on line.
 

jpanhalt

Joined Jan 18, 2008
7,871
may use the attached schematic 6 side by side, common drain automatic comes out when mounting them on one plate.
????? Not necessarily.
1) Heat sinks can be insulated (anodizing is an good insulator, BTW)
2) I still can't see your schematic. Headed to Walmart's for +5.50 reading glasses.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
166
????? Not necessarily.
1) Heat sinks can be insulated (anodizing is an good insulator, BTW)
2) I still can't see your schematic. Headed to Walmart's for +5.50 reading glasses.
The board looks like this:

post101.JPG
 

jpanhalt

Joined Jan 18, 2008
7,871
LAOADAM said:
trying to make a 6 way mosfet switch, each mosfet working separately and independent.
Thanks for the edit. You only show ONE 3205 (post #4). What about the other 5 working independent[sic]?
 

dendad

Joined Feb 20, 2016
2,986
Often, with a group of FETs close together like that, a strip of silicone insulation is used between the FETs and the heatsink, then they are all clamped to the heatsink using a bar that is screwed down at each ens. The bar runs across the plastic body of the FETs.
Ur, special spring loaded clips are used...


Here you can see the strip of grey silicone insulation, and a screwdriver being used to remove a clip.

Google "TO220 Insulation" for many pictures.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
166
Thanks for the edit. You only show ONE 3205 (post #4). What about the other 5 working independent[sic]?
I'll 6 of that
Often, with a group of FETs close together like that, a strip of silicone insulation is used between the FETs and the heatsink, then they are all clamped to the heatsink using a bar that is screwed down at each ens. The bar runs across the plastic body of the FETs.
Ur, special spring loaded clips are used...


Here you can see the strip of grey silicone insulation, and a screwdriver being used to remove a clip.

Google "TO220 Insulation" for many pictures.

actually, the point of my question is is it necessary to insulate the mosfet piece by piece?
 

dendad

Joined Feb 20, 2016
2,986
actually, the point of my question is is it necessary to insulate the mosfet piece by piece?
Yes. All must be insulated from the heat sink and each other.
Unless, of course, you use FETs with isolated tabs.
Even if all the tabs are electrically connected together in the circuit, I'd advise insulating them anyway so there is no power on the heat sink. It can then be connected to the chassis.
 

Alec_t

Joined Sep 17, 2013
10,355
In your post #4 circuit the FET is a low-side switch for the LED load. If you connect all 6 drains together you won't have independent low-side control of 6 loads.
 
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