Thoughts on other FET’s?

Are there any features that you would like to add to the VESC?
lizardmech
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Location: Australia

Re: Thoughts on other FET’s?

Postby lizardmech » 07 Dec 2016, 16:18

slapshot136 wrote:
lizardmech wrote:These are a good alternative to direct fets, easier to solder at home. Direct fet package has lower thermal resistance on the top but less on the bottom. While the FDMT800 isn't as good on the top but retains low resistance to PCB.

http://mouser.com/ProductDetail/Fairchi ... MT80060DC/
You can buy them directly of the fairchild website for less if you want a batch of them.


Thermal issues aside, are they any better? I see the rdson is 1.1mOhm - was asking more as a direct replacement for the v4.12 hardware than for an entirely new design

Silicon mosfets are pretty mature technology, all you can do is get different packages. The large 60V ones will all be 0.8-1.2 mohm. You will perhaps get slightly less capacitance on the newer packages. You might actually be able to swap the FDMT800 fets onto a vesc 4x board if the gate pin is on the same side, I soldered them to quite a few other SMD mosfet footprints.

All the latest developments are on SiC and GaN mosfets but they're extremely expensive and mostly aimed at 600V rather than low RDSon at low voltage.

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Thoughts on other FET’s?

Postby rew » 08 Dec 2016, 09:25

lizardmech wrote:Thermal issues aside, are they any better? I see the rdson is 1.1mOhm - was asking more as a direct replacement for the v4.12 hardware than for an entirely new design

You gain a factor of 1.4 due to the lower RDSON. Then you lose a factor of two due to the higher thermal resistance. But if you want you can try. I think you can hack these chips on the IRFS7530 footprint.

lizardmech
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Location: Australia

Re: Thoughts on other FET’s?

Postby lizardmech » 08 Dec 2016, 15:01

They should be better if you mount a heatsink on the top that way they are cooled both sides. It makes them useful in situations like vesc 4x when there isn't mush space underneath for cooling.

slapshot136
Posts: 27
Joined: 15 Sep 2016, 18:24

Re: Thoughts on other FET’s?

Postby slapshot136 » 08 Dec 2016, 18:56

rew wrote:
lizardmech wrote:Thermal issues aside, are they any better? I see the rdson is 1.1mOhm - was asking more as a direct replacement for the v4.12 hardware than for an entirely new design

You gain a factor of 1.4 due to the lower RDSON. Then you lose a factor of two due to the higher thermal resistance. But if you want you can try. I think you can hack these chips on the IRFS7530 footprint.


Isnt the form factor the same for the IPB010N06N and IRFS7530?

rew
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Re: Thoughts on other FET’s?

Postby rew » 09 Dec 2016, 09:18

The last suggestion I saw was "hacked SO8 footprint". My design has a separate powerstage, I have a DPAK-7 (IRFS7530 and friends) power stage and an SO8 footprint powerstage. The SO8 fits all sorts of hacked SO8 footprints.
Once these start selling, I will create a "dual SO8-like" PCB allowing a further reduction of the RDSON....

lizardmech
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Joined: 19 Jan 2016, 10:54
Location: Australia

Re: Thoughts on other FET’s?

Postby lizardmech » 09 Dec 2016, 15:12

slapshot136 wrote:
rew wrote:
lizardmech wrote:Thermal issues aside, are they any better? I see the rdson is 1.1mOhm - was asking more as a direct replacement for the v4.12 hardware than for an entirely new design

You gain a factor of 1.4 due to the lower RDSON. Then you lose a factor of two due to the higher thermal resistance. But if you want you can try. I think you can hack these chips on the IRFS7530 footprint.


Isnt the form factor the same for the IPB010N06N and IRFS7530?

They're only 1mm or so thick and they have a metal pad on the top to mount heatsinks to. Just remember to use a dielectric, the pad is bonded to mosfet source section.

rew
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Location: Delft, Netherlands.

Re: Thoughts on other FET’s?

Postby rew » 10 Dec 2016, 12:16

You're thinking of another infineon mosfet. I might have made the same mistake a while back.... The IPB010N06N is a DPAK7 just like the IRFS7530, with a plastic case.

slapshot136
Posts: 27
Joined: 15 Sep 2016, 18:24

Re: Thoughts on other FET’s?

Postby slapshot136 » 11 Dec 2016, 18:36

rew wrote:You're thinking of another infineon mosfet. I might have made the same mistake a while back.... The IPB010N06N is a DPAK7 just like the IRFS7530, with a plastic case.


So for the same package, DPAK7, if I just wanted to replace the days on a v4.12 board, without changing the cooling, would it improve the average current by 1.4x? Would the max frequency also improve? Any other changes in performance on the v4.12 hardware mosfet swap?

rew
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Joined: 25 Mar 2016, 12:29
Location: Delft, Netherlands.

Re: Thoughts on other FET’s?

Postby rew » 12 Dec 2016, 22:35

I have read the optimos fet datasheet a bit more carefully than before. On the one hand, it has a few parameters a bit better than the IRFS7530. However, either they are less exaggerating the ratings than IR, or their mosfet acutally performs less in practice.

the IRFS7530 can handle peaks of 1400A, while the IPB can only handle half that. The silicon limit of the IRFS is similarly twice as high as the IPB. So..... If you want you can try, but for me it's a toss as to which one will turn up to perform better in this application.

The IPB says it is meant for synchronous rectification. IF that means 60Hz operation that might explain low RDSON but overall not quite as good as expected performance.

rutgerv
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Joined: 09 Jan 2017, 12:18

Re: Thoughts on other FET’s?

Postby rutgerv » 30 Jan 2017, 12:01

I was just wondering, can the IRFS7530 in the VESC design easily be swapped for a different FET, without requiring changes to hardware or software? I'm planning a fairly low power application (approximately 5 amps peak at 24V) that the IRFS7530s seem overkill for. Bringing down the cost would be an additional benefit, it this would be possible.

Rutger


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