High Voltage/Amp Transistors Pinball

wayneh

Joined Sep 9, 2010
17,153
You need load-balancing resistors as mentioned by @ScottWang. As is, there’s nothing to keep one transistor from taking the majority of the current. It’ll happen eventually.
 

Thread Starter

adam450

Joined Mar 19, 2019
29
Even with .1Ohm ballast resistors and separate base resistors, one of the transistors steals all the current and burns up. I would think that if one had a breakdown the other one would be a little bit hot but I tried this with 3 transistors and 2 were cold, as if they never got any current.

upload_2019-6-8_16-28-16.png
 

wayneh

Joined Sep 9, 2010
17,153
Even with .1Ohm ballast resistors and separate base resistors, one of the transistors steals all the current and burns up. I would think that if one had a breakdown the other one would be a little bit hot but I tried this with 3 transistors and 2 were cold, as if they never got any current.
Odd. I can only speculate that 0.1Ω is maybe not enough to shut down the one transistor that is hogging the current. Try a 0.2Ω if you have one.
 

Ylli

Joined Nov 13, 2015
1,053
I'd drop the base resistors to perhaps 120 ohms. The TIP120's have an typical Hfe of 1000, but being Darlingtons they also have a Vbe(on) spec of up to about 2.5 volts. That doesn't leave much to drop across those base resistors. .........and without going back over the thread.... Do you have a fast diode across the coil? Want to be sure the transistors are not being fried by the flyback voltage.
 

Thread Starter

adam450

Joined Mar 19, 2019
29
I'll try some of the suggestions. Yes I have a normally spec'd diode for 48V solenoids. I don't recall specifically which one.

I had some leftover IRF3205's and I picked up an NTE2390 today. Both MOSFETS.

Confusingly, the NTE2390 I can pull massive current (10A) for at least 5 seconds (probably more) and I tried on two of them. Both good. It gets hot but it doesn't break down. However, my old IRF3205's still will never work. They die immediately and I'm looking at the datasheets and they look pretty similar. I bought the IRF3205 off ebay so they could just be bad as people say dont buy off Ebay, but these guys look pretty similar on the datasheet. The RDS on the NTE part says .2, but I dont know if that is .2 milliOhm or what. If so that would make sense that it doesn't have as much resistance and why it holds up so well.

I'm putting 5V on their gate. Both TO-220 packages.
https://www.nteinc.com/specs/2300to2399/pdf/nte2390.pdf
http://www.irf.com/product-info/datasheets/data/irf3205.pdf
 
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Ylli

Joined Nov 13, 2015
1,053
Rds on the 2390's look like 0.2 ohms. Quite high. But that might be limiting dI/dT, and so may be saving the part. Try adding a 0.1 or 0.2 ohm resistor in series with the solenoid when using the 3205's. The 3205 should be the more rugged part. .
 

ronv

Joined Nov 12, 2008
3,770
I'll try some of the suggestions. Yes I have a normally spec'd diode for 48V solenoids. I don't recall specifically which one.

I had some leftover IRF3205's and I picked up an NTE2390 today. Both MOSFETS.

Confusingly, the NTE2390 I can pull massive current (10A) for at least 5 seconds (probably more) and I tried on two of them. Both good. It gets hot but it doesn't break down. However, my old IRF3205's still will never work. They die immediately and I'm looking at the datasheets and they look pretty similar. I bought the IRF3205 off ebay so they could just be bad as people say dont buy off Ebay, but these guys look pretty similar on the datasheet. The RDS on the NTE part says .2, but I dont know if that is .2 milliOhm or what. If so that would make sense that it doesn't have as much resistance and why it holds up so well.

I'm putting 5V on their gate. Both TO-220 packages.
https://www.nteinc.com/specs/2300to2399/pdf/nte2390.pdf
http://www.irf.com/product-info/datasheets/data/irf3205.pdf
If your only going to use 5 volts to drive them you probably should use logic level FETS.
https://www.mouser.com/datasheet/2/427/SUP85N10-240141.pdf
 
When paralleling the TIPs, I would math Hfe to at least 10%. You would have to measure it and select based on measurements, You need the emitter resistor too. Something like 2% tolerance metal oxide.
 

ScottWang

Joined Aug 23, 2012
7,070
nte2390 is not a logic level Vgs and the Vgs=±10V, so when the Vgs=3.3V then the Rds will be too high and the Vds also too high as 3V, please check the "Drain−Source ON−Voltage" on page 2.

irf3205 I can't find the info to shows that it is a logic level Vgs, but the Vgs=4.5V, you still can get the Ids current as 25A, when the Vgs<4.5V then I can't the useful information.
Page 2 -- RDS(on), Static Drain-to-Source On-Resistance ––– ––– 8.0 mΩ, Vgs = 10V, ID = 62A.

@ronv
SUP85N10-240141 -- When the Vgs <3.5V then maybe it is not a good choice for this application.
SUP85N10-240141_VgsAndId_Page3_ScottWang.jpg

SSR-40DD 40A -- if you want then maybe it is suitable for you.

Another choice is that to use a stage of npn bjt (ie : 2N3904) and a P MOSFET, Vds>=48V*1.5V, Ids(on)>=12A, Rds(on)<=12 mΩ.
 
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Sensacell

Joined Jun 19, 2012
2,904
It's painful to try to drive a low-side NFET or Transistor with 3.3V logic, especially when several amps are involved.
If it's a FET, you have a very limited selection of devices that can turn fully ON with 3.3V.
Transistors need substantial base drive current, hard to get from a 3.3V IO pin.

IF... you can configure your coil for a high-side switch (one side of the coil grounded), this circuit will do the job nicely.

The NPN transistor acts as a current sink and level shifter for the FET, it pulls around 5 ma into ground, which provides a nice 12 volts Vgs on the FET, regardless of the 48 V supply. (2400 ohms X 0.005 A = 12V)

Now the selection of the FET is easy, with a solid 12V on the gate, there are zillions of PFETS to chose from.

The only caveat is that it's not blazing fast, as long as you are not trying to do Khz PWM on the coil, it's plenty fast enough.
 

Attachments

ronv

Joined Nov 12, 2008
3,770
nte2390 is not a logic level Vgs and the Vgs=±10V, so when the Vgs=3.3V then the Rds will be too high and the Vds also too high as 3V, please check the "Drain−Source ON−Voltage" on page 2.

irf3205 I can't find the info to shows that it is a logic level Vgs, but the Vgs=4.5V, you still can get the Ids current as 25A, when the Vgs<4.5V then I can't the useful information.
Page 2 -- RDS(on), Static Drain-to-Source On-Resistance ––– ––– 8.0 mΩ, Vgs = 10V, ID = 62A.

@ronv
SUP85N10-240141 -- When the Vgs <3.5V then maybe it is not a good choice for this application.
View attachment 179358

SSR-40DD 40A -- if you want then maybe it is suitable for you.

Another choice is that to use a stage of npn bjt (ie : 2N3904) and a P MOSFET, Vds>=48V*1.5V, Ids(on)>=12A, Rds(on)<=12 mΩ.
It's painful to try to drive a low-side NFET or Transistor with 3.3V logic, especially when several amps are involved.
If it's a FET, you have a very limited selection of devices that can turn fully ON with 3.3V.
Transistors need substantial base drive current, hard to get from a 3.3V IO pin.

IF... you can configure your coil for a high-side switch (one side of the coil grounded), this circuit will do the job nicely.

The NPN transistor acts as a current sink and level shifter for the FET, it pulls around 5 ma into ground, which provides a nice 12 volts Vgs on the FET, regardless of the 48 V supply. (2400 ohms X 0.005 A = 12V)

Now the selection of the FET is easy, with a solid 12V on the gate, there are zillions of PFETS to chose from.

The only caveat is that it's not blazing fast, as long as you are not trying to do Khz PWM on the coil, it's plenty fast enough.
I'm putting 5V on their gate. Both TO-220 packages.
 

djsfantasi

Joined Apr 11, 2010
7,866
You still
I'm putting 5V on their gate. Both TO-220 packages.
You still need a logic level MOSFET. With only 5 volts on the gate, the MOSFET won’t turn fully on and at your high amperage, will soon overheat. And could burn up.

You need a component that satisfies all of your requirements. I looked for logic level n-channel MOSFET rated for at least 60V and more than 60A.

Here is a logic level n-channel MOSFET that satisfies those requirements.
 

mvas

Joined Jun 19, 2017
538
Actually on NTE's website their product says .2Ohm for RDS(on), so that's interesting.
Did you notice, the circuit design on the older shematics ...
a) They turn the Solenoid Driver Transistor ON very quickly but
b) They turn the Solenoid Driver Transistor OFF more slowly?

Now, do you suppose their design has something to do with long-term reliability ?
 
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ScottWang

Joined Aug 23, 2012
7,070
I'm putting 5V on their gate. Both TO-220 packages.
I knew that you were put the 5V on gate, what I thought was that the 3.3V is came from I/O port of uC, so I will count the Vin as 3.3V, 5V just for test, if the TS want to use 5V as Vin and shift 3.3V to 4.5V or 5V then use SUP85N10-240141 should be OK.
 

ScottWang

Joined Aug 23, 2012
7,070
You still need a logic level MOSFET. With only 5 volts on the gate, the MOSFET won’t turn fully on and at your high amperage, will soon overheat. And could burn up.

You need a component that satisfies all of your requirements. I looked for logic level n-channel MOSFET rated for at least 60V and more than 60A.

Here is a logic level n-channel MOSFET that satisfies those requirements.
Although the datasheet of SUP85N10-240141 didn't mention that it is a logic level MOSFET, but it was mentioned like there:
Rds(on)=0.0105 mΩ at Vgs = 10V,
Rds(on)=0.012 mΩ at Vgs = 4.5 V, here you can treat it as a logic level n-channel MOSFET, it was shown on the page 1 of the datasheet.

So you can see the Rds(0n) doesn't shown too much difference, what you care about is the heat sink also does not that much difference when it is working on 3.5A.

When I compared SUP85N10-240141 with FDP5800, the big difference is that the parameters of FDP5800 is better than SUP85N10-240141, such as the Vds, Ids, Rds, label or mention it as a logic level Vgs is not a problem here.
 

ronv

Joined Nov 12, 2008
3,770
I knew that you were put the 5V on gate, what I thought was that the 3.3V is came from I/O port of uC, so I will count the Vin as 3.3V, 5V just for test, if the TS want to use 5V as Vin and shift 3.3V to 4.5V or 5V then use SUP85N10-240141 should be OK.
Yeah, your right. We have both numbers.
But the 3.3 would explain why the Darlington didn't work either.
 
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