The LM317 is quite the hot head ...

**stj** · 06-04-2017, 02:18 PM

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

another way to control the LM317 would be an i2c controlled digital pot.

**eccerr0r** · 06-04-2017, 02:43 PM

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

Full circle

**EasyGoing1** · 06-04-2017, 04:20 PM

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

Originally posted by eccerr0r

I suppose I have way too much scrap to scavenge from now, though I did spend quite a bit from Jameco to fill the shelves...

OK WOW ... I've been buying this stuff from amazon or ebay ... I didn't even know about Jameco and looking at their stuff, I can get these parts for practically nothing ... shipping will probably cost more than the parts...

Downloaded their catalog and have been looking through it ... i'm impressed.

**eccerr0r** · 06-04-2017, 05:03 PM

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

Well, I'm not saying that Jameco has the best parts - they sell Chongx and Jamcon (I don't know if they're proud of this brand) capacitors as part of their "Jameco Valuepro" for heaven's sake - but if you want to focus on cheap, they've been pretty decent. Also their grab bags can be a good assortment of random parts.

Else you'll have to go with the usual Digikey/Mouser.

**EasyGoing1** · 06-06-2017, 12:22 AM

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

Originally posted by kc8adu

use a mosfet switch and disconnect the cell with it.

Could you give me part number examples of a ‘mosfit switch'?

**EasyGoing1** · 06-06-2017, 12:24 AM

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

Originally posted by eccerr0r

Else you'll have to go with the usual Digikey/Mouser.

I've never priced anything at DigiKey, but I use them a lot for data sheet downloads ... their web site has the feel of being a company that only caters to bulk buyers ... do they do onzie twozie type sales without charging out the nose for shipping to make up for the low value invoice?

**EasyGoing1** · 06-06-2017, 12:25 AM

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

Originally posted by stj

another way to control the LM317 would be an i2c controlled digital pot.

Actually, in my OP, you’ll notice that I’ve already done this and was simply thinking there could be a better way ... also, the number of wires needed for the digital pot ... man!

**EasyGoing1** · 06-06-2017, 04:48 AM

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

Originally posted by stj

how big is your heatsink?

That's a little personal, don't you think?

lol

I dunno ... maybe 1.5” squared

**EasyGoing1** · 06-06-2017, 07:44 AM

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

Originally posted by kc8adu

use a mosfet switch and disconnect the cell with it.

Do you think that this layout would work CONCEPTUALLY???

Since my Arduino can only output 3.3v, and the power MOSFET that I have is fully on at 4 volts, I thought maybe controlling the mosfet using a 3904 off of a 5v source with a voltage divider might be a sensible way to go about it... ???

Attached Files

**budm** · 06-06-2017, 08:51 AM

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

Where did you get that circuit?Look at the Voltage divider of the 220 Ohms and the 1200 Ohms resistor and how that transistor is connected and the effect of the Voltage on the Gate will be when the transistor is turned on which it will never be on since the Emitter Voltage is higher than the Base Voltage so the Transistor is in reverse bias if the output of the iC in high state is only 3.3V.

**EasyGoing1** · 06-06-2017, 09:16 AM

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

Originally posted by budm

Where did you get that circuit?

I made it from scratch.

Originally posted by budm

Look at the Voltage divider of the 220 Ohms and the 1200 Ohms resistor and how that transistor is connected and the effect of the Voltage on the Gate will be when the transistor is turned on which it will never be on since the Emitter Voltage is higher than the Base Voltage so the Transistor is in reverse bias if the output of the iC in high state is only 3.3V.

That confirms my readings after building it just now...

I was thinking that I wanted to get 4 volts to the gate of the MOSFET using a 3.3v pin on the Arduino ... let me re-think it and see what I can come up with.

**budm** · 06-06-2017, 09:24 AM

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.

**EasyGoing1** · 06-06-2017, 09:34 AM

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

Originally posted by budm

which it will never be on since the Emitter Voltage is higher than the Base Voltage so the Transistor is in reverse bias if the output of the iC in high state is only 3.3V.

What about this ... though I think I need to re-calc the resistors ...

Attached Files

**EasyGoing1** · 06-06-2017, 09:43 AM

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

Originally posted by budm

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.

**EasyGoing1** · 06-06-2017, 09:59 AM

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.

**mariushm** · 06-06-2017, 10:15 AM

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** · 06-06-2017, 11:51 AM

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

Originally posted by mariushm

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?

Attached Files

**budm** · 06-06-2017, 12:47 PM

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** · 06-06-2017, 02:48 PM

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

Originally posted by budm

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** · 06-06-2017, 07:22 PM

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?

The LM317 is quite the hot head ...

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