The LM317 is quite the hot head ...

[EasyGoing1]

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

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 ...

[budm]

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]

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

Where did you get that circuit?

I made it from scratch.

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]

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]

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

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... ???

[EasyGoing1]

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

how big is your heatsink?

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

lol

I dunno ... maybe 1.5” squared

[EasyGoing1]

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

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]

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

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]

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

use a mosfet switch and disconnect the cell with it.

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

[eccerr0r]

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]

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

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]

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

Full circle

[stj]

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

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

[kc8adu]

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

how are you terminating the charge cycle?
when in cv mode you need to watch current and cut it off at about 50ma for a typical 18650.
use a mosfet switch and disconnect the cell with it.
then it does not matter if your 317 can hit 0.
this also prevents issues with the 317 getting voltage to its output when off without the drop of a diode.
do not float charge li-ion.

[eccerr0r]

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

You'll have to look around for a LM358 or LM324, they are fairly common (they've been around almost as long as LM741).

MC3043, LM2904, TS271/TS272/TS274 are alternatives. A RRIO LM6142 or TLV2371/TLV2372/TLV2374 will work but are overkill. The LM741 is an ancient chip that has so many drawbacks, but the rail problem is not one of the most serious ones (there are many other low noise op amps that also don't go to rail that are commonly used due to noise and input characteristics where the LM358 is not so great at). You may find a LM358 in old crappy ATX power supplies like Deer used to generate PG. Good power supplies likely use a supervisory chip instead and not have that op amp.

The NE555/LM555 is a very common chip, it's an all purpose timer chip. Due to its output characteristics, it can be used to make charge pumps like in
http://www.electronicecircuits.com/e...supply-circuit .

And I don't know if you have a large capacitor on the input else you may be backpowering the LM317 which is harmful. A protection diode across input and output (anode on output, cathode on input) can protect against back powering.

Unfortunately likely you will have to go buy parts unless you have a lot of junk to scavenge from... 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...

[EasyGoing1]

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

Easier to just use a LM358 instead of the LM741.

Would you happen to know if the 358 is common in any specific electronics that I might have laying around ??? I feel like I'm doing my part when I salvage stuff rather just buying more ... not to mention a bird in the hand ... three days for shipping is murder for a US citizen ... lol

- create a charge pump of some sort to synthesize the negative voltage, perhaps using a 555 or some switching regulator.

No 555's laying around and everything else you said you may as well have been speaking chinese.... charge pump?? this is a real thing in electronics?

Yes, it also generates some inductive back EMF too. A small vibrator motor probably doesn't generate that much however.

The reason I asked about that, is because I built a small little 317 variable buck converter kinda thing ... in fact this is the circuit I used:



I forget the values for the voltage divider, but the second resistor is a pot ... 5k I think ... anyways ... whats happening is that Ill use the thing ... three or four times over maybe a weeks time then allofasudden, I plug it in and its passing ALL of the source voltage and the resistor on he adjustment pin does nothing... so if im feeding it 12 volts then thats whats at the output of the 317 ... so if I then replace the 317 with another one ... it works beautifully till suddenly ill plug it in and it only passes the source voltage ... till I replace the 317... I am now on my 5th 317 the last three happening in the last month... this could bel

No letting the smoke out and no stressing of the 317 has happened at all ... it never once got hot ... so i was thinking maybe when I run those motors ... then shut it down ... they might be hitting the 317 from the wrong side which would explain me no seeing the problem util the next time I plug it in. Other than that im stumped

[eccerr0r]

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

See now you're starting to make sense ... where does one conjure up ... negative voltage ... exactly??? Some kind of voodoo?

Easier to just use a LM358 instead of the LM741.

Else you'll either
- build another power supply and connect it backwards (or another winding on the transformer). You can use a 9V or even a few batteries to generate it in the mean time.
- create a charge pump of some sort to synthesize the negative voltage, perhaps using a 555 or some switching regulator.

You know the tiny motors that operate the vibration mechanism in a gaming controller ??? ... if I were driving that with a 317, do those motors pose the same risk to a 317 as a coil does to a transistor in terms of blow back once power is disconnected? Should the motor have a protection diode on it?

Yes, it also generates some inductive back EMF too. A small vibrator motor probably doesn't generate that much however.

[EasyGoing1]

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

You know the tiny motors that operate the vibration mechanism in a gaming controller ??? ... if I were driving that with a 317, do those motors pose the same risk to a 317 as a coil does to a transistor in terms of blow back once power is disconnected? Should the motor have a protection diode on it?

[EasyGoing1]

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

Using the 741 you will need a negative supply to rid of this bottom end issue.

See now you're starting to make sense ... where does one conjure up ... negative voltage ... exactly??? Some kind of voodoo?

[eccerr0r]

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

Check the voltage at the input of the 741 (keep in mind the impedance of your multimeter will load down the circuit, even if you have a 10Mohm DMM). See if it is doing the range you expect. Check this for the top end.

If you're insisting on using a 741, you will have some nonlinear operation as you see at bottom end due to the inherent issues with the 741. Using the 741 you will need a negative supply to rid of this bottom end issue.