The LM317 is quite the hot head ...

[EasyGoing1]

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

3.3V Vgs is not going to cut it based on your graph in post 66. BTW, how did you come up with 220 Ohms GS resistor? You know what Vds, Vgs are, right?

I just arbitrarily chose 220 because from what I’ve read, the only thing that matters, is that the gate be able to go ground should the arduino pin ever float for whatever reason. Because from my experimentation, you can apply a voltage to the gate and if you take it away, the mosfet stays ON ...

Vds = Voltage between drain and source
Vgs = Voltage between gate and source

I took two years of electronics and even passed my CET ... but that was in 1992. Since then, Ive done nothing with that education, but rather became a Novell CNE in 1995 and have been a network engineer ever since. Only recently have I begun to experiment with electronics again. I remember doing calculations for transistor circuits, I remember doing nodal circuit analysis, Thevenoms theorem, Kirckhoffs laws etc., I even took a year of electrical calculus ... I just seem to have forgotten most of it. BUT, what I haven’t lost, is my ability to re-learn, nor my curiosity for it.

[eccerr0r]

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

Power Schottky Rectifiers are for the output stages of forward switching regulator converters.

And here's a suggestion for the level shifter (I did not do much validation on component selection but at first glance it should work and saturate the mosfet. That +12V must be clean and not exceed the maximum gate voltage of the mosfet or you'll kill it.) This is the same old schematic as before except I drew more on it...

[budm]

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

3.3V Vgs is not going to cut it based on your graph in post 66. BTW, how did you come up with 220 Ohms GS resistor? You know what Vds, Vgs are, right?

[EasyGoing1]

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

What would use one of these for? Something called a “Power Schottky rectifier”??? I've got a few of those.

[EasyGoing1]

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

Don't know what you attached but doesn't seem to be related to irfp460

here's datasheet for irfp460: https://cdn.badcaps-static.com/pdfs/...7e5d86dcce.pdf

note Vgs up to 4v (min 2v, max 4v), your mosfet may or may not turn on (fully) with 3.3v and 4200pF input capacitance seems huge.

also strictly related to that graph picture, those values are for Tambient of 25c which won't ever happen during operation

This is what I was using

[mariushm]

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

The way I read the graph, its good for 10 amps at 3 volts

See?

Vgs are those lines, the graph shows only Vgs starting from 4v, your 3.3v Vgs isn't even in that graph picture.

something cheap and good for around 5A continuously : https://www.digikey.com/product-deta...ICT-ND/2052800

or something for ~12a : https://www.digikey.com/product-deta...DKR-ND/3458181

[mariushm]

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

May have found a better solution ... was scouring through my regulators / mosfets and found an IRFP460 ... look at the graph on this bad boy...



I think we might have a winner...

Don't know what you attached but doesn't seem to be related to irfp460

here's datasheet for irfp460: https://cdn.badcaps-static.com/pdfs/...7e5d86dcce.pdf

note Vgs up to 4v (min 2v, max 4v), your mosfet may or may not turn on (fully) with 3.3v and 4200pF input capacitance seems huge.

also strictly related to that graph picture, those values are for Tambient of 25c which won't ever happen during operation

[EasyGoing1]

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

Will 1A be sufficient? At 3.3V it's below the rated threshold though slightly above the minimum spec (used for Ids leakage estimates). You'll need a level shifter or find another FET. Or you could use a power darlington but the characteristics might not be sufficient...

The way I read the graph, its good for 10 amps at 3 volts

See?

[eccerr0r]

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

Will 1A be sufficient? At 3.3V it's below the rated threshold though slightly above the minimum spec (used for Ids leakage estimates). You'll need a level shifter or find another FET. Or you could use a power darlington but the characteristics might not be sufficient...

[EasyGoing1]

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

So with that, I'm thinking this is how its gonna work... maybe?

[EasyGoing1]

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

May have found a better solution ... was scouring through my regulators / mosfets and found an IRFP460 ... look at the graph on this bad boy...



I think we might have a winner...

[EasyGoing1]

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

So if the Vbe is around 0.9V then what do you think the Voltage will be at the Emitter of that Transistor based on your last diagram?

OH I think I see grasshoppah .... Should I remove the 220Ω from base to ground? cause like that, it should about 1 volt minus Vbe - right?

And possibly lower that resistor value so that it would give me like 1.7 volts cause the Vbe should be roughly .7 volts?

[delaware74b]

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

Both Digikey and Mouser will ship priority mail (1 pound max, no more than 3 business days after order is processed). Mouser charges $7.99 and Digikey charges $7.50. They will ship just 1 item but it makes sense to make a larger order so your parts total is more than the shipping. I always try to spend at least $30 before shipping.

[budm]

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

So if the Vbe is around 0.9V then what do you think the Voltage will be at the Emitter of that Transistor based on your last diagram?

[EasyGoing1]

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

Well, ask yourself this: I have 1VDC between circuit GND and the BASE of the NPN Transistor 2N3904, what will my DCV at the Emitter and circuit GND of the Transistor has to be so it will be biased ON?
]

According to the data sheet, it has to be like .9 volts ..

[budm]

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

Well, ask yourself this: I have 1VDC between circuit GND and the BASE of the NPN Transistor 2N3904, what will my DCV at the Emitter and circuit GND of the Transistor has to be so it will be biased ON?
Look up Emitter follower.
http://fourier.eng.hmc.edu/e84/lectures/ch4/node9.html
https://en-sg.knowledgebase.renesas....wer_circuit%3F
https://cdn.badcaps-static.com/pdfs/...2475f71559.pdf
http://www.falstad.com/circuit/e-follower.html

[EasyGoing1]

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

Can't you pick a better mosfet?

The one you chose has quite big gate capacitance and high gate threshold voltage (4v)... why not pick one that is guaranteed to turn on at less than 3.3v and simply connect it directly to an output pin.

Cause I have like ... 15 of these ... ill see if I have any others....

What about this layout?

[mariushm]

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

Can't you pick a better mosfet?

The one you chose has quite big gate capacitance and high gate threshold voltage (4v)... why not pick one that is guaranteed to turn on at less than 3.3v and simply connect it directly to an output pin.

Use a decent resistor between gate and ground to discharge the gate to quickly turn it off when needed.

[EasyGoing1]

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

OK, I’m reading a few articles on it ... lemmie see if I can figure this out.

[EasyGoing1]

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

What are you trying to accomplish? Turning the MOSFET fully on when its needed and fully off when its needed, or PWM? I think you need to understand how to bias transistor on and how to turn it off, if you understand that then you will see why that transistor is off with the Voltage as shown in your diagram, need to understand the basic first.

I want the MOSFET fully on when it’s needed and fully OFF when its not needed ... and that state I want to control with by turning the 3.3v pin from the Arduino on or off.

AND the MOSFET that I have is not fully on until there is 4 volts at the gate.