MOSFET burning up but similar circuit on another board is fine

[zacaj]

I'm trying to make a simple solenoid driving board for a pinball project, but running into problems. The basic requirement is to be able to repeatedly pulse 50V coils for about 100ms or less each time. I looked up the schematics for how some commercial boards do it, and found two nice examples:

Based on these two designs I prototyped a similar single circuit with an IRL540N (equivilant to the STP22NE10l), a 10k pulldown, and a 160 ohm discharge resistor, controlled by the GPIO on a PIC32, but I found that within a few pulses (each a second apart) the fet becomes too hot to touch and soon begins to smoke.

Trying to find any other differences, I realized that the PIC32 was 3V, but these other boards were 5V (and the IRL540N doesn't really saturate till around 5-6V), so I looked for some other chip I could use to step up the voltage, and ended up with a 74ACT04N hex inverter (the inverter part doesn't matter, I just invert my signals from the PIC32). It has a low enough input voltage threshold that I can control it with the PIC32 while having it output 5V for the fet. However, although the fet lasted a bit longer, within a few pulses it'd still get too hot.

Of course, lowering the coil voltage or using a weaker coil makes it heat up less, but that's not really an option. Plus, the first circuit above runs at 70V, so there must be something else wrong if I can't manage at 50V.

I tried varying the resistance of my discharge resistor with various values between 150 (which is what I've seen recommended for mosfets) and 50k ohms, but that didn't make any difference.

I've tried comparing my 7404 with the latches used in the other designs, but I can't see any relevant differences. They're all (I think?) push-pull outputs, capable of 20mA+ (my 7404 can do more current than either of the latches), they operate on the same voltage...

Does anyone have any suggestions as to what the difference here might be?

 

[dorke]

Welcome to EP.

You identified the problem correctly : the Mosfet doesn't saturate.

But your solution is wrong:
1. You can't operate a 74ACT04N or a 7404 at 3.3V they need 5V VCC(they are speced at 5V).
2. In any case, a logic device operated at 3.3V VCC can't produce an output higher than 3.3V,
so it is the same as driving the MOSFET from the PIC32 directly.
3. The drive current is not an issue since the MOSFET gate is extremely high impedance
(practically zero current).

The way to go is drive the gate with a "true 5V logic" that is VCC=5V .
If you have that voltage it is immediate, otherwise create one.

 

[Harald Kapp]

Show us your own circuit, looking at similar circuits doesn't help that much.

 

[Harald Kapp]

But your solution is wrong:
1. You can't operate a 74ACT04N or a 7404 at 3.3V they need 5V VCC(they are speced at 5V).

My understanding is that he used the 74ACT04 as a level shifter, operating it from 5 V. Otherwise you'd be correct.

 

[kellys_eye]

Choose, specifically, logic-level MOSFETs that are designed to be fully saturated at the appropriate logic voltages (5V). They are common enough.

 

[Alec_t]

Why the caps on the FET gates? They will slow down the switching action and increase the heat generated.

 

[zacaj]

My understanding is that he used the 74ACT04 as a level shifter, operating it from 5 V. Otherwise you'd be correct.

Correct, sorry I didn't make that clearer. The VCC of the 7404 is connected to 5V, so when I ground its input from the PIC it supplies 5V to the gate of the fet.

Show us your own circuit, looking at similar circuits doesn't help that much.

Choose, specifically, logic-level MOSFETs that are designed to be fully saturated at the appropriate logic voltages (5V). They are common enough.

Is the IRL540N not logic level? I was under the impression it was.

Why the caps on the FET gates? They will slow down the switching action and increase the heat generated.

I'm not sure why they did that instead of using pulldowns. I based my design off the first example which used pulldowns as it made more sense

 

[Harald Kapp]

Is the IRL540N not logic level? I was under the impression it was.

Vgsth(max) = 2 V -> yes, logic level compatible.

Your schematic shows a bipolar transistor, not a MOS transistor. Assumig an NMOS in the correct orientation the circuit looks o.k. on paper.

I based my design off the first example which used pulldowns as it made more sense

The 74ATC04 has a push-pull output, pull-downs are not really required in operation. They are useful, however, when the low voltage circuit is not powered to definitely turn-off the MOSFETs.

The ground of the solenoid power supply (70 V) is connected to ground of the logic circuit?

 

[Audioguru]

The VCC of the 7404 is connected to 5V, so when I ground its input from the PIC it supplies 5V to the gate of the fet.

No Way! A lousy old 7404 output high is 2.4V minimum, no where near 5V. You need a 74HC04 which is high speed Cmos and its output goes up to its supply voltage.

EDIT: You said 7404 and you also said 74HCT04 which is high speed Cmos with an output that goes up to its supply voltage. Which is it?

 

[BobK]

Are you sure you got IRL and not IRF540? The IRL540 is logic level, IRF is not.

How much current is the solenoid drawing?

What is the voltage on the gate when turned on in your circuit?

What current does the solenoid draw?

Bob

 

[Audioguru]

The Mosfets that were burning up were probably cheap Chinese fake ones from ebay.

 

[kellys_eye]

I misread the device as the IRF540 (since I use them quite regularly) but the IRL is definitely logic level.

 

[zacaj]

The 74ATC04 has a push-pull output, pull-downs are not really required in operation. They are useful, however, when the low voltage circuit is not powered to definitely turn-off the MOSFETs.

I know, just want to be on the safe side if anything went wrong.

The ground of the solenoid power supply (70 V) is connected to ground of the logic circuit?

Yes. Not sure it'd even work otherwise...

EDIT: You said 7404 and you also said 74HCT04 which is high speed Cmos with an output that goes up to its supply voltage. Which is it?

It's a 74ACT04. I've been abbreviating it in subsequent posts.

Are you sure you got IRL and not IRF540? The IRL540 is logic level, IRF is not.

Definitely IRL540N.

How much current is the solenoid drawing?

I'm not great with the math for inductors, but it's about a 2ohm coil, running at ~45VDC. Regardless, if the other boards can drive this coil without issue, I should be able to too.

The Mosfets that were burning up were probably cheap Chinese fake ones from ebay.

I got them from digikey. I've tried three separate batches from different years that I had on hand. I've replaced at least one of the fets

in the original boards I'm basing mine off and it worked fine with one of my digikey ones.

What is the voltage on the gate when turned on in your circuit?

4.94VDC.

Links to datasheets:
74ACT04N: http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=SN74ACT04&fileType=pdf
74HCT574: https://assets.nexperia.com/documents/data-sheet/74HC_HCT574.pdf
74HCT273: https://assets.nexperia.com/documents/data-sheet/74HC_HCT273.pdf
IRL540N: https://www.infineon.com/dgdl/irl540n.pdf?fileId=5546d462533600a40153565fbd752565

By my understanding the ACT should work similarly enough to the HCT for this use, am I correct?

 

[Audioguru]

An old 7404 TTL IC with a minimum output high of only 2.4V is completely different to a modern 74HC04 or 74ACT04 which are Cmos and have outputs that go up to the supply voltage.

The IRL540 that overheated was either defective or it was an IRF540 marked wrong.

 

[zacaj]

An old 7404 TTL IC with a minimum output high of only 2.4V is completely different to a modern 74HC04 or 74ACT04 which are Cmos and have outputs that go up to the supply voltage.

Luckily it's a 74ACT04 then.

The IRL540 that overheated was either defective or it was an IRF540 marked wrong

I've gone through 12 of them so far trying to fix this issue. They're not defective

 

[(*steve*)]

The IRL540 that overheated was either defective or it was an IRF540 marked wrong.

Since we now know where they came from, it may be time to get off this particular high horse for a while.

 

[Audioguru]

You replaced one Mosfet on an original board with one of the Mosfets from Digikey and it worked fine.
But 12 Mosfets from Digikey burned up in your circuit. Then something is wrong with your circuit, not the Mosfets.
Maybe there is a different set of solenoids? Try your circuit driving the solenoids that work fine with the original circuit.

 

[zacaj]

But 12 Mosfets from Digikey burned up in your circuit. Then something is wrong with your circuit, not the Mosfets.

That's what I'd assume, yes. But I can't figure out how my circuit differs.

Maybe there is a different set of solenoids? Try your circuit driving the solenoids that work fine with the original circuit.

I've tested with a few coils, including one that was previously connected to the original circuit, and it hasn't made a difference.

 

[(*steve*)]

I would be interested in a few measurements and/or details.

1. What is the voltage across the MOSFET when it is turned on (and in the process of "burning up". I would attach a heatsink to the MOSFET for this test.
2. Is the solenoid actuating?
3. What is the actual Vgs when the MOSFET is turned on (no need for a load for this test)
4. What is the actual Vgs when the MOSFET is turned off.
5. Does the MOSFET get hot when when the solenoid is supposed to be turned off?
6. What frequency is the MOSFET being switched at? Or is the MOSFET turned on and off for long periods (perhaps for periods not less than 100ms)?

 

[Audioguru]

Is the original circuit made on a compact printed circuit board but you made yours on a solderless breadboard with messy wires all over the place?