The LM317 is quite the hot head ...

[budm]

Re: The LM317 is quite the hot head ...

BTW, if you look at that graph, at 10A of Id and Vds of 3V, that is 30W of power dispensation, so you will have temperature rise above the room temperature, that rise is based on thermal resistance of the device rating in xxC per Watt. You also do not want the junction temp to be above the limit as shown in the spec.

[mariushm]

Re: The LM317 is quite the hot head ...

What about something like this? FDP7030 N-Channel Logic Level Power MOSFET?

Corrected the url linking, you had a weird " character there.

Yeah, that mosfet should work fine with 3.3v though the gate capacitance is a bit on the high side (it should work fine i think).

[EasyGoing1]

Re: The LM317 is quite the hot head ...

Open your datasheet:
LTC1154 datasheet , especially at the bottom of page 6 where you see the block diagram, which shows you how the IC has a gate charge and discharge control logic and fast/slow gate charge mechanisms.

Interesting, thank you for taking the time to explain that to me.

Mike

[EasyGoing1]

Re: The LM317 is quite the hot head ...

Corrected the url linking, you had a weird " character there.

Yeah, that mosfet should work fine with 3.3v though the gate capacitance is a bit on the high side (it should work fine i think).

I picked that one because pf the four logic level power mosfets that Mouser had, it was the least expensive at $1.20 or so. The most expensive one was like $11

[mariushm]

Re: The LM317 is quite the hot head ...

Digikey has a huge selection of mosfets, but maybe shipping is more expensive.

Digikey can also filter by Vgs and Rdson and average current all those specs that you can play around with

Here's ALL n-channel mosfets filtered by lowest price if you order 10 of them : https://www.digikey.com/short/3d24j0

The price for 1 may be a bit higher (you can see it on the mosfet details page), I selected 10 pcs minimum for you so that you wouldn't get in the list of results mosfets that can only be bought in full rolls of 1000-2500 pcs.

Play with Vgs(th) (Max) @ Id (ex select all <= 3.5v for example) and then select the maximum continuous current you want (so that you'd filter out parts that can only do less current than what your project will do) and then pay attention to drive to source voltage max drain / source voltage and then look in datasheets to see the actual performance for your Vgs of 3.3v (and try to get mosfets with lower gate capacitance but don't stress yourself too much)

For reasonable currents, i see something as cheap as 30-40 cents and easy to use.

For example, see PMV16XNR: https://www.digikey.com/product-deta...0-1-ND/5395602

It can do at least 4A continuously with very low Vgs (1v and up) , up to almost 7A with higher Vgs (let's say 2.5v and up) as long as there's some surface around the chip to act as heatsink

here's another good example: AON7406 : https://www.digikey.com/product-deta...7-1-ND/1856080

max 2.4v Vgs (at 3v it can do 10A or more with Vds above 1v) and it's also cheap, less than 0.5$ if you buy 1. Package looks scary but it would be easy to solder.

[redwire]

Re: The LM317 is quite the hot head ...

This guy made an animated javascript circuit simulator, seems like some fun: http://www.falstad.com/circuit/circuitjs.html
There is a mosfet to play with, but not a logic-level one.

[EasyGoing1]

Re: The LM317 is quite the hot head ...

https://www.digikey.com/short/3d24j0[/url]

For example, see PMV16XNR: https://www.digikey.com/product-deta...0-1-ND/5395602

here's another good example: AON7406 : https://www.digikey.com/product-deta...7-1-ND/1856080

... Package looks scary but it would be easy to solder.

Yeah it does ... surface mount stuff ... haven't messed with components like that yet...

Do you know if there is an alternative to the LM317 that is just as cheap and easy to use? Just curious about what else might be out there in terms of programmable / changeable voltage regulators.

[mariushm]

Re: The LM317 is quite the hot head ...

The pmv16xnr is very tiny but the pins are spaced far apart that you can get some prototyping board, put three blobs of solder on some through holes on the prototyping board and then just tin the pins and then heat up the blobs of solder and make contact between the pins and the blobs of solder. It's easy.

The AON7406 is scarier but again it's easy to solder. You only have 3 wires going to it, gate (1 pad) , source (3pads) and drain (the big metal stuff) ... so you can put the three wires flat over the pads and solder the wires easily to the pads.


As for lm317 alternatives... There's literally tens of thousands of chips, linear or of switching type

60.000+ linear regulators : https://www.digikey.com/products/en/...ors-linear/699

26.000+ switching regulators : https://www.digikey.com/products/en/...regulators/739

For linear regulators,
pick maximum current,
pick dropout voltage (in order to provide smooth output voltage, input voltage must be higher or equal to dropout voltage + output voltage),
pick minimum input voltage the regulator must be able to accept (for example you filter out regulators that can only work with up to 6v, if you want to adjust voltage up to 10-11v)
pick package to account for how easy it would be to keep them cool (regulators dissipate the difference between input voltage and output voltage as heat - some regulators say they can do so much current, but in reality that's only if the input voltage is very close to output voltage, for example max 6v in , 5v out at 3a for a total of 3 watts of heat dissipated)

[PeteS in CA]

Re: The LM317 is quite the hot head ...

1. How did you determine that at 4 Vgs, there will never be a Drain current larger than 1.5 amps?

2. 25C is 77F ... and if it can sustain 10 amps and remain at that temperature, then I can’t see why it would be improbable for it to sustain 3 amps at room temperature, unless the amount of current it can handle significantly decreases with each degree of temperature increase, but in most cases, the temperature that the device will be in (in this case anyways) wont be much higher than 77F.



3. Do you have any in mind that I can get at Amazon?

1. By looking at the curve for V(GS) = 4V. The vertical axis is Drain current; the horizontal axis is V(DS). With a V(GS) of 4V, the curve doesn't go higher that ~1.5A.

2. Those curves are for junction temperature, not ambient temperature. Elsewhere in the datasheet, it specifies a junction to case thermal resistance. That means that if the device is dissipating power, the junction temperature - the temperature of the silicon die - will always be higher than the temperature of the case. On top of that thermal resistance there is the thermal resistance between the case and the heatsink, and the thermal resistances from the heatsink to ambient air. All those thermal resistances together mean that if the silicon die is dissipating 30W, that silicon die has to be hotter than the room ambient temperature (unless the device is being cooled by a refrigerated liquid).

MOSFET makers publish that junction-case thermal resistance. Insulator manufacturers specify the thermal resistance of their insulators. Heatsink manufacturers publish the thermal resistance vs. airflow curves for their dissipators. Fan manufacturers publish the airflow vs. back pressure curves for their fans. Actual airflow can be measured with anemometers. All in all, design engineers can calculate the junction temperature rise for their power devices to choose heatsinks and fans that can keep the junction temperature within a desired range (if the ambient is 40C instead of 25C, the junction temperature will be ~15C higher).

3. You would do better to go to device manufacturers' websites, pick several possibilities, and see what is available. Also, I'd go with Digi-Key or Newark over Amazon.

Right now, EG1, I think your focus needs to be on what different types of devices do, how they can be used, and how they operate. I've noticed that even university engineering programs (e.g. San Jose State) give those fundamentals short shrift. Without that foundation, you'll have trouble recognizing and understanding the importance and meaning of information such as the thermal resistance or datasheet curves. I'm not being critical. You're probably wa-a-a-a-aaaaayyyyy over my head when it comes to network and computer stuff; OTOH, power electronics has been my career field for over 35 years, and much of what I've learned was by doing, hands on, over that time.

[budm]

Re: The LM317 is quite the hot head ...

1. By looking at the curve for V(GS) = 4V. The vertical axis is Drain current; the horizontal axis is V(DS). With a V(GS) of 4V, the curve doesn't go higher that ~1.5A.

2. Those curves are for junction temperature, not ambient temperature. Elsewhere in the datasheet, it specifies a junction to case thermal resistance. That means that if the device is dissipating power, the junction temperature - the temperature of the silicon die - will always be higher than the temperature of the case. On top of that thermal resistance there is the thermal resistance between the case and the heatsink, and the thermal resistances from the heatsink to ambient air. All those thermal resistances together mean that if the silicon die is dissipating 30W, that silicon die has to be hotter than the room ambient temperature (unless the device is being cooled by a refrigerated liquid).

MOSFET makers publish that junction-case thermal resistance. Insulator manufacturers specify the thermal resistance of their insulators. Heatsink manufacturers publish the thermal resistance vs. airflow curves for their dissipators. Fan manufacturers publish the airflow vs. back pressure curves for their fans. Actual airflow can be measured with anemometers. All in all, design engineers can calculate the junction temperature rise for their power devices to choose heatsinks and fans that can keep the junction temperature within a desired range (if the ambient is 40C instead of 25C, the junction temperature will be ~15C higher).

3. You would do better to go to device manufacturers' websites, pick several possibilities, and see what is available. Also, I'd go with Digi-Key or Newark over Amazon.

Right now, EG1, I think your focus needs to be on what different types of devices do, how they can be used, and how they operate. I've noticed that even university engineering programs (e.g. San Jose State) give those fundamentals short shrift. Without that foundation, you'll have trouble recognizing and understanding the importance and meaning of information such as the thermal resistance or datasheet curves. I'm not being critical. You're probably wa-a-a-a-aaaaayyyyy over my head when it comes to network and computer stuff; OTOH, power electronics has been my career field for over 35 years, and much of what I've learned was by doing, hands on, over that time.

+10, especially 'I think your focus needs to be on what different types of devices do, how they can be used, and how they operate."
You cannot skip the basic and there is no stop in learning, and hands on is the great learning tool.

[EasyGoing1]

Re: The LM317 is quite the hot head ...

The pmv16xnr is very tiny but the pins are spaced far apart that you can get some prototyping board, put three blobs of solder on some through holes on the prototyping board and then just tin the pins and then heat up the blobs of solder and make contact between the pins and the blobs of solder. It's easy.

These are being marketed as “Arduino Power MOSFET Switches” etc.

They're $16 for 10 on Amazon.

[mariushm]

Re: The LM317 is quite the hot head ...

Those were marked as discontinued/obsolete around 2011 I think - some guy probably has a few thousand of them old stock (from some project he didn't finish or something like that) and he put them as Amazon listing.

The modern replacement seems to be FQP30N06L which is 11$ for 10pcs : https://www.digikey.com/product-deta...06L-ND/1055122

Add 6-8$ for shipping and you're at the same price but at least you know you get genuine and relatively new parts (these don't stay on shelves for a long time at a distributor like Digikey)

If you can live with only 30v Vds , this one is 0.6$ in 10pcs and will work just fine : https://www.digikey.com/product-deta...893-ND/2606361

I gave you Digikey and the link to a huge selection of mosfets, just use the filtering mechanism to pick what you want. If you're afraid of surface mounted components just filter them out (select through-hole only, there's an option there to the right)
Here's all n-channel mosfets that are through hole , play around with filters and check datasheets like I explained and you'll find plenty that would fit your needs.

[EasyGoing1]

Re: The LM317 is quite the hot head ...

Those were marked as discontinued/obsolete around 2011 I think

This one should work, right? I can get 10 for like $8