# MOSFET AND IGBT fail in pwm speed control for 260VDC 2200W universal motor

#### strantor

Joined Oct 3, 2010
5,543
no i am calculating the value as i need 10 amps
It doesnt work that way. The terminal resistance of the motor is a real value, you cannot calculate it. You need to measure that resistance and then use ohms law to figure out how many amps the motor will instantaneously draw if you apply 260 v to it

#### strantor

Joined Oct 3, 2010
5,543
The diode in that circuit is not between source and drain it is between source and gate. It is a zener diode, used to ensure that no overvoltage is applie to the gate. The 6a rectifier diod serves no purpose in this instance and would actually be better if you use that 6a diode as your freewheeling diode if thats all you have

#### kandilx

Joined Oct 21, 2011
69
The diode in that circuit is not between source and drain it is between source and gate. It is a zener diode, used to ensure that no overvoltage is applie to the gate. The 6a rectifier diod serves no purpose in this instance and would actually be better if you use that 6a diode as your freewheeling diode if thats all you have
sry again not this one i meant this one the diode D1

edit : ok it seems that it is the site problem or so , open this link http://www.electronics-tutorials.ws/transistor/tran_7.html
you will find what i mean under title "
Simple Power MOSFET Motor Controller"

#### strantor

Joined Oct 3, 2010
5,543
I see no D1. I see ZD1, near the bottom, and that's the one I'm talking about. its a zener diode.

#### kandilx

Joined Oct 21, 2011
69
It doesnt work that way. The terminal resistance of the motor is a real value, you cannot calculate it. You need to measure that resistance and then use ohms law to figure out how many amps the motor will instantaneously draw if you apply 260 v to it
the resistance across the motor terminal is 2.6 ohms so it draws ~ 100 A instantaneously ?

#### strantor

Joined Oct 3, 2010
5,543
the resistance across the motor terminal is 2.6 ohms so it draws ~ 100 A instantaneously ?
yes.....

#### praondevou

Joined Jul 9, 2011
2,942
i really dont see any difference between this one and the previous one as there is only one ground so com is already connected to it and vss too
As far as I can see from the datasheet, COM and VSS are not internally connected. So if I supply VCC with the same voltage as VDD I also need to connect COM to VSS.
Can you please post a complete diagram of what you have connected right now or at the moment when your last MOSFET died.
If you have a zener at the gate and the gate resistor is too small then of course the 2110 will heat up as you are probably drawing too much current out of it.

Take the zener out, you don't need it if VCC is 12V.

You also said your MOSFET lasts a few seconds, but doesn't get hot, so for me it doesn't look like an overcurrent, more like overvoltage from drain to source, even though I may be wrong. Consider also lead /trace/wire inductance.
On the other hand, the IRFP has a max pulsed current rating of 74A, continuous 18A....

#### kandilx

Joined Oct 21, 2011
69
I see no D1. I see ZD1, near the bottom, and that's the one I'm talking about. its a zener diode.
this image was a little bit tricky so i get it a shot check the attachment

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#### praondevou

Joined Jul 9, 2011
2,942
this image was a little bit tricky so i get it a shot check the attachment
I would actually put a clamping network on my MOSFET directly from drain to source... an RCD voltage clamp for example.

#### strantor

Joined Oct 3, 2010
5,543
this image was a little bit tricky so i get it a shot check the attachment
Ah, yes I see. it says it's to suppress overvoltages, so good idea to have it I guess.

I agree praondevou that if it were overcurrent it would be hot, but having never blown one up, I have no idea how hot things need to get before they blow, or how long it takes to get that hot. I am speculating that a couple of seconds of exceeding the current rating by a factor of 5 could cause the junction to heat to the point of failure in less time than it takes for said heat to migrate to the surface of the package where one can feel a "hot chip". It also sounds as you said like an overvoltage. assuming the freewheeling diode is functioning correctly, the inductive spike when the FET switches off should not exceed the 260V on the other side of it. But I have little confidence that the diode is functioning properly [you need an oscope] as I think it severely underspecified for the job. so there could be huge mosfet killing transients there.

#### kandilx

Joined Oct 21, 2011
69
As far as I can see from the datasheet, COM and VSS are not internally connected. So if I supply VCC with the same voltage as VDD I also need to connect COM to VSS.
Can you please post a complete diagram of what you have connected right now or at the moment when your last MOSFET died.
If you have a zener at the gate and the gate resistor is too small then of course the 2110 will heat up as you are probably drawing too much current out of it.

Take the zener out, you don't need it if VCC is 12V.

You also said your MOSFET lasts a few seconds, but doesn't get hot, so for me it doesn't look like an overcurrent, more like overvoltage from drain to source, even though I may be wrong. Consider also lead /trace/wire inductance.
On the other hand, the IRFP has a max pulsed current rating of 74A, continuous 18A....
first image is circuit i am testing and the other image explain that both point pointed by arrows are grounded

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#### kandilx

Joined Oct 21, 2011
69
Ah, yes I see. it says it's to suppress overvoltages, so good idea to have it I guess.

[you need an oscope] as I think it severely underspecified for the job. so there could be huge mosfet killing transients there.
i am trying to get access the university lab to test with the oscope

#### strantor

Joined Oct 3, 2010
5,543
i am trying to get access the university lab to test with the oscope
lol, good deal.

#### strantor

Joined Oct 3, 2010
5,543
first image is circuit i am testing and the other image explain that both point pointed by arrows are grounded
hey I don't see any freewheeling diodes(diode across the motor terminals). you are using a freewheeling diode, right?

#### kandilx

Joined Oct 21, 2011
69
hey I don't see any freewheeling diodes(diode across the motor terminals). you are using a freewheeling diode, right?
yes yes i used it one across the motor and the other across the mosfet but i? forgot about them because they are not on the bread board but on the vetor board i wonder since it could be over voltage that i use zener diode with high voltage 270 ~300v ?

#### kandilx

Joined Oct 21, 2011
69
here is it again

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#### strantor

Joined Oct 3, 2010
5,543
yes yes i used it one across the motor and the other across the mosfet but i? forgot about them because they are not on the bread board but on the vetor board i wonder since it could be over voltage that i use zener diode with high voltage 270 ~300v ?
well, the rectifier diode across your motor (freewheeling) *should* prevent voltage spikes from the motor killing your mosfet, but if we think that's not working, then a 270V zener from drain to source *should* absorb whatever the freewheeling diode doesn't take care of. I think you may be underestimating how robust these diodes need to be, and how much current you are dealing with. Also your wires should be as short as possible, as these overvoltages are caused in no small part by inductances in the wiring. if you minimize the wiring, you minimize the inductance, and you minimize the spikes. also, your capacitors; I was going to touch on this earlier, but what kind of capacitors are you using? You need a bank of capacitors for this. and not just any capacitors, they need to be extremely low ESR, high ripple current capacitors. These capacitors will help to minimize the transients and provide standby current while switching.

#### kandilx

Joined Oct 21, 2011
69
well, the rectifier diode across your motor (freewheeling) *should* prevent voltage spikes from the motor killing your mosfet, but if we think that's not working, then a 270V zener from drain to source *should* absorb whatever the freewheeling diode doesn't take care of. I think you may be underestimating how robust these diodes need to be, and how much current you are dealing with. Also your wires should be as short as possible, as these overvoltages are caused in no small part by inductances in the wiring. if you minimize the wiring, you minimize the inductance, and you minimize the spikes. also, your capacitors; I was going to touch on this earlier, but what kind of capacitors are you using? You need a bank of capacitors for this. and not just any capacitors, they need to be extremely low ESR, high ripple current capacitors. These capacitors will help to minimize the transients and provide standby current while switching.
which capacitor are you talking about the motor comes with dc cap 0.22uF
do i need more or wht and will it give the mosfet more safty ?

#### strantor

Joined Oct 3, 2010
5,543
which capacitor are you talking about the motor comes with dc cap 0.22uF
do i need more or wht and will it give the mosfet more safty ?
This is where my knowledge gets shifty. As I said, I've never actually done this, only been studying on it for the past month. I am in the middle of building my own motor controller and these are the caps I picked out.
http://www.datasheetarchive.com/indexdl/Datasheets-SW6/DSASW00103136.pdf

That selection was based on a personal recommendation so I really don't know how to determine just how much you really need. the more the better. My instincts tell me that one .22μF capacitor is probably not enough. maybe someone else can help you (and me) with this.

#### praondevou

Joined Jul 9, 2011
2,942
which capacitor are you talking about the motor comes with dc cap 0.22uF
do i need more or wht and will it give the mosfet more safty ?
The 220nF on the motor terminal only makes sense to suppress sparks inside the (brushed) motor when the brushes connect and disconnect to the commutator.

Strantor was probably talking about the capacitor in the attached picture which I marked with "C" near the MOSFET.

Have a look at this picture and tell us if your layout is more or less like it.
Everything colored needs to be SHORT wires/traces, especially the power part. This means that the freewheeling diode of the motor should be placed according to the picture and not directly on the motor terminals as this would increase the length of the inductances that cause voltage spikes. If you don't have "C" then the wires to the battery should be short too.
The bypass caps on the 2110 need to be mounted adjacent to the chip.
the high side parts, like diode and caps you actually don't need since the bootstrap cap won't be charged anyway and you don't use this output.

I attached a second picture where this gets more clear. The inductances of all wires where the motor current goes through will create a reversed voltage on them when you turn off the MOSFET. That means that you'll have a bigger voltage from drain to source as just your power supply voltage. (I didn't draw the motor, but it's freewheeling diode is conducting because the motor itself is an inductance just the way all the wires are.)
You see also that the diode you put on the MOSFET will not conduct, it would if your motor was between the legs of a fullbridge.

If you want to to protect the MOSFET from voltage spikes use a snubber, this could be RC, RCD or anything else that limits the voltage Vds. But since you can't measure it, it's all guesswork.

As Strantor said overcurrent may also be a reason, but I'm not so sure about it since you managed to burn even the IGBT from your first post.

EDIT: just saw that strantor was talking about IGBT snubber capacitor modules directly mounted on the switch, these are snubbers , not just capacitors, from what I understand.

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