Exploding high current MOSFETS

Thread Starter

stobby

Joined Jun 20, 2018
26
Hey everyone,

I have made a circuit to convert straight dc to dc square wave at relative low voltage (30v) but high current (around 200amps). I have trialed this circuit at 12vdc with a spotlight as the load and it works perfectly. however when it i trialed it at higher power levels the Mosfet's almost instantly exploded and or cracked. These mosfet's are rated at 55v, 169amps.

As for cooling, There are 4 of these mosfets on a large water cooled aluminum heat sink.

I am driving the gates at 12v around 300hz, so i am fairly sure they are hard switching.

pulse welder.JPG
Here's the circuit diagram.
Mosfet's = International rectifier IRF1405PbF, here's a link to the data sheet, https://www.alliedelec.com/m/d/036c4829fe1cdc1aa06c26f2750d2805.pdf
R1 = 47Ohm
R2 = 10kohm
R3 = indicates load.
 

Sensacell

Joined Jun 19, 2012
2,837
Those FET's have a ton of input capacitance, and it adds in parallel.

Your gate drive might be driving them too slowly, spending too much time in the linear mode where the power dissipation is massive.
All the heat sink in the world won't help if you exceed the safe operating area of the FET for long.

You should be using a gate driver that can source and sink a few amps to get the gates to charge and discharge quickly.

Gate drive for this kind of power switching quickly becomes non trivial.
 

Thread Starter

stobby

Joined Jun 20, 2018
26
Thanks for the reply's,

To drive the Mosfet's i have a signal generator outputting its signal to a 2N6122 transistor, with its source coming from a 12v battery charger. The output of this transistor then goes to the gate rail of schematic above. I did this as the signal generator can only provide 30ma by it self.

IMG_1969.jpg
IMG_1970.jpg
IMG_1971.jpg
 

drc_567

Joined Dec 29, 2008
1,114
... The package limitation current, given in the datasheet, is only 75 amperes. (note #6 under Source to Drain ratings.) The figure of 169 amps has something to do with the maximum permissible junction temperature.
 

danadak

Joined Mar 10, 2018
4,057
You are driving 10,000 pf of gate C, not counting miller effect, and limiting
gate drive. So MOSFETs spending a long time in linear region. Seriously
consider a gate driver. And a low L layout to make sure you have clean
switching to the gates.

Using a light load for the MOSFETs can you grab some scope shots of
the gate drive transient ? Also there is no ballasting in the MOSFETs
so MOSFET device to device differences can easily have one MOSFET
bearing most of the load.

https://www.infineon.com/dgdl/para.pdf?fileId=5546d462533600a401535744b4583f79

https://assets.nexperia.com/documents/application-note/AN11599.pdf


Regards, Dana.
 

wayneh

Joined Sep 9, 2010
17,152
Your switching from low to high may be OK, probably should be better, but consider what happens when your signal goes low. All of the gate capacitance has to be drained away by R1 and R2 in series. Way too slow.
 

kubeek

Joined Sep 20, 2005
5,753
What is the load? You are missing a freewheeling diode, and at that kind of current even just the lead inductance could cause high voltage across the mosfet and destroy them.
 

crutschow

Joined Mar 14, 2008
27,243
Have you tried putting the load on the other side?
As a source-follower circuit?
That means the gate voltage would need to be about 10V above the supply voltage using a high-side gate driver.
MOSFET device to device differences can easily have one MOSFET
bearing most of the load.
MOSFETs have a positive coefficient of ON resistance versus temperature so they tend to self balance the currents when in parallel.
This is opposite of BJT's in parallel where one transistor will tend to hog the current.
 

mvas

Joined Jun 19, 2017
538
Hey everyone,

I have made a circuit to convert straight dc to dc square wave at relative low voltage (30v) but high current (around 200amps). I have trialed this circuit at 12vdc with a spotlight as the load and it works perfectly. however when it i trialed it at higher power levels the Mosfet's almost instantly exploded and or cracked. These mosfet's are rated at 55v, 169amps.

As for cooling, There are 4 of these mosfets on a large water cooled aluminum heat sink.

I am driving the gates at 12v around 300hz, so i am fairly sure they are hard switching.

Here's the circuit diagram.
Mosfet's = International rectifier IRF1405PbF, here's a link to the data sheet
R1 = 47Ohm
R2 = 10kohm
R3 = indicates load.
MOSFETs can self-balance when in parallel, only when they are turned ON and OFF at essentially the same time.
The gates on these MOSFET's are not being driven hard.
Therefore, the chance of "balancing" is ... not likely.
The Gate Drive Circuit shown in the schematic is a design that will blow-up MOSFET's.

Use a pair of Dual MOSFET Gate Drivers ( something like this ) ...
https://www.infineon.com/cms/en/product/power/gate-driver-ics/irs4427/?redirId=65104

Maybe, even consider a Gate Driver that sink / source: 4 amps or even 5 amps.
Add Low ESR capacitors to provide the amps needed to drive these gates very quickly.

How to select the proper MOSFET Gate Driver
https://www.electronicproducts.com/Analog_Mixed_Signal_ICs/Selecting_the_right_MOSFET_driver.aspx

NOTE: IRF1405 PACKAGE LIMITATION IS 75 AMPS per MOSFET !
The first MOSFET on, or the last MOSFET off, has a big problem.
 
Last edited:

kubeek

Joined Sep 20, 2005
5,753
Paralleling mosfets to switch huge currents is no easy task, and doing it the naive way is a sure way to do it many times over.
If the OP can´t provide the actual way it is connected, and now again looking at the first post where the only way to discharge the gates is a 10k resistor to ground, no wonder it releases the magic smoke on a regular basis.
 

wayneh

Joined Sep 9, 2010
17,152
Paralleling mosfets to switch huge currents is no easy task, and doing it the naive way is a sure way to do it many times over.
If the OP can´t provide the actual way it is connected, and now again looking at the first post where the only way to discharge the gates is a 10k resistor to ground, no wonder it releases the magic smoke on a regular basis.
Yup, I noted that in #11 and I’d bet it’s the biggest part of the problem.
 

Thread Starter

stobby

Joined Jun 20, 2018
26
... The package limitation current, given in the datasheet, is only 75 amperes. (note #6 under Source to Drain ratings.) The figure of 169 amps has something to do with the maximum permissible junction temperature.
Ahh, you found the hidden secret, I would consider that a major spec, not a 'note'. keen eye.

The high side source is a 250amp transformed MIG welder with a tapped voltage selector. The load is obviously the arc between the gun and material. I am trying to achieve a pulsed MIG welder without the extravagant price tag of machines with that capability. So the long story short i am trying to convert straight DC from the machine and transform it into square wave.
Unfortunately i don't have access to a scope at this stage.

I did think that R2 is probably a little high, maybe a 1kohm instead?

As for packages could anyone recommend something more suitable, How about these block style mosfet's they seem a bit stronger.
R1258043-01.jpg
here's the data sheet https://docs-apac.rs-online.com/webdocs/157c/0900766b8157c9bd.pdf
 

Janis59

Joined Aug 21, 2017
1,332
1) it may be the wild oscillation on gates between Cgs and wite 10 nH per cm of length, subGHz frequencies and grand energies released on gate in microseconds.
2) it may be lack of dampfer hang-ons at Your construction, them are mandatory between S and D in any kind of power circs. Minimum is resistor plus capacitor, but best case diode included.
3) it may be a bad identicality of mosfets and fact You missed a small resistors in the S before paralelling. Its not so important as for bjt, but anyway it saves the multitude of headaches after.
 

shortbus

Joined Sep 30, 2009
8,593
I am trying to achieve a pulsed MIG welder without the extravagant price tag of machines with that capability
You do know that term "pulsed Mig" is a misnomer and marketing hype don't you? By its nature, all Mig is pulsed it is so by the way the filler wire melts on contact and then feeds into the work again. Doing this make it a series of pulses.
Adding a electronic pulse won't in any way make either your welds or you as a welder better. That only comes from practice and good training.
 
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