Implementing adjustable voltage

[Nuck]

I have tried and tested a fairly simple way of adding user adjustable voltage control to a mod. The pieces are pretty cheap (I got mine at digikey.com)

I'm still a real novice at the circuit stuff so I have to give credit to RjG for offering a TON of advice and suggestions on this and damn never every other problem I run into while modding.

Parts

LM317 chip (I used a TO 220 version so the pins I explain will use this one)
Digi-Key - LM317TFS-ND (Fairchild Semiconductor - LM317T)

220 ohm resistor
330 ohm resistor

500 ohm potentiometer (there are a bunch to select from, these ones are pretty cheap...next time I will get a better quality)
Digi-Key - 3306P-501-ND (Bourns Inc. - 3306P-1-501)

Notes: The resistors are used to set and control the voltage chip. You can use a wide range of values and will set the min and max voltage values. Here is a good site that lets you play with the values and shows the basic circuit.

LM 317 Calculator


Wiring

The capacitors for our application can safely be ignored so to get it nice and small I do the following:

Note: Orient the LM317 flat with the legs pointing at yourself to determine which pin is left in the following instructions.

1. Wire the 220 resistor between the left leg(adjustment pin) and the back plate (alternate voltage out)
2. When looking at the potentiometer pins with the centre pin down, wire the 330 resistor between the left leg of the LM317 (adjustment pin) and the right pin on the potentiometer.
3. Wire the centre pin of the potentiometer to a ground
4. Wire the voltage supply to the right pin of the LM317 (voltage in)
5. The voltage out can be picked up anywhere off the back plate of the LM317 or from the centre pin (voltage out) of the chip.

That's it. The resistors and pots I use control the voltage within 3.1 to 6v and are adjustable with a small screwdriver to access the exposed adjustment screw of the pot.

 

[Laredo7mm]

...control the voltage within 3.1 to 6v...

What input voltage are you using?

The spec sheet for the LM317 shows a voltage drop out of about 2.75V when the load is drawing 1.5 amps.

 

[Nuck]

What input voltage are you using?

The spec sheet for the LM317 shows a voltage drop out of about 2.75V when the load is drawing 1.5 amps.

I'm using 2xcr123a which read about 8.2 volts when fresh. The dropout should be 2.25-2.50 at that level but I will test under load tonight. The drop decreases as the Vin decreases so the losses should scale down.

I'll run a bunch of tests when I complete the battery box I plan to use for testing. Hopefully the range will be acceptable since the next step is to add adapters that will allow the same mod to use any atomizers.

If the losses are too great then I may have to use a standard 6v regulator with a switch to turn it off. Luckily I have a set of 5v and 6v regulators that will be here during the week.

 

[mogur]

Very nice circuit, Nuck. Your reference to the Electronics Lab 317 calculator is excellent, also. Another great one to play with is-

Martin E. Meserve - K7MEM - LM317 Voltage Regulator Designer

If someone wants a finer control, narrower range of adjustment, a 560Ω resistor and a 200Ω pot would give you 4.38v - 5.57v output.

Yeah, the dropout voltage is a problem if you're going with 6 volts to the atomizer. The 317 usually drops 2.5 volts at an amp. And a 7806 drops 2.0 volts. That's fine at 2 x 4.2 volts, but you'll hit cutoff when the CRs reach 4.0v each and below. My atomizers (RN4075) fry at 5 volts, so I have more wiggle room.

 

[Laredo7mm]

I'm using 2xcr123a which read about 8.2 volts when fresh. The dropout should be 2.25-2.50 at that level but I will test under load tonight. The drop decreases as the Vin decreases so the losses should scale down.

I'll run a bunch of tests when I complete the battery box I plan to use for testing. Hopefully the range will be acceptable since the next step is to add adapters that will allow the same mod to use any atomizers.

If the losses are too great then I may have to use a standard 6v regulator with a switch to turn it off. Luckily I have a set of 5v and 6v regulators that will be here during the week.

I couldn't find the specs on the relationship between Vin and the drop out. The only info in the spec sheet was drop out versus current. If you are going to run a 3.7 ohm atomizer at 6 volts, the amps would be 1.63 and you will see more than 2.5V drop out (according to the curves in the specs). I don't think you will be able to sustain the 6V out with a 8.2 Vin.

Take a look at the LDO (low drop out) adjustable regulator from Texas Instruments. They also make fixed voltage output models. They have about 0.45V drop out at 3 amps load. Here is a link:

Linear Regulators - Single Channel LDO - UCC383-ADJ - TI.com

 

[Laredo7mm]

Hey Nuck, I am not trying to bust your %#$@, just trying to help.

I am not an electronics expert by any means. Just look at my post on the PV Pak preview thread. I have built six boards now, and it still isn't quite right (stupid touch switch). Electronics does not come natural to me, I am more of a mechanical type person.

Let us know how your load test results come out. I think voltage regulators are a nice way to go and having an adjustable one would be a nice feature.

 

[surbitonPete]

Those links to the calculators made me wonder if anyone knows of any good free electronic circuit design and test software?? Perhaps educational?

 

[breakfastchef]

This should keep you mildly entertained for a bit.

Free Electronics resouces: tutorials, datasheets, software, websites - Freebyte's Guide to
Circuit Symbols of Electronic Components
Electronic Circuit Design and Simulation Software, Power Supply Calculators
Downloads - Circuit Design - Emulation

Those links to the calculators made me wonder if anyone knows of any good free electronic circuit design and test software?? Perhaps educational?

 

[surbitonPete]

Thanks breakfastchef....I shall check those out.

 

[Nuck]

I couldn't find the specs on the relationship between Vin and the drop out. The only info in the spec sheet was drop out versus current. If you are going to run a 3.7 ohm atomizer at 6 volts, the amps would be 1.63 and you will see more than 2.5V drop out (according to the curves in the specs). I don't think you will be able to sustain the 6V out with a 8.2 Vin.

Take a look at the LDO (low drop out) adjustable regulator from Texas Instruments. They also make fixed voltage output models. They have about 0.45V drop out at 3 amps load. Here is a link:

Linear Regulators - Single Channel LDO - UCC383-ADJ - TI.com

I built a quick bat box to use for testing and set the pot to 5.5v. I'm running tests down the range of voltages. I did test the low and high range immediately and I'm smoking like a maniac to wear the bats and test the full range. Here is what I have so far:

V in 8.08, V out 5.50, V load 5.07
V in 4.00, V out 2.90, V load ----

The loss scaled down to 1.1v at the lower end but was still too big a loss.

Thanks for link btw, I was looking everywhere for a low drop out that still handled higher current.

 

[Nuck]

Hey Nuck, I am not trying to bust your %#$@, just trying to help.

I am not an electronics expert by any means. Just look at my post on the PV Pak preview thread. I have built six boards now, and it still isn't quite right (stupid touch switch). Electronics does not come natural to me, I am more of a mechanical type person.

Let us know how your load test results come out. I think voltage regulators are a nice way to go and having an adjustable one would be a nice feature.

No problem man, I didn't think you were and I honestly appreciate any advice or criticism you can provide. I've been following the PV Pak thread closely and am amazed at the work you've been doing.

 

[Laredo7mm]

OK, now I understand what you ment by the voltage drop scaling with Vin. In the case of an atomizer or any fixed resistance load, this is correct. A 3.7 ohm atomizer running at 4V will put a 1.08 amp load on the regulator. The same atty at 6V will draw 1.62 amps. Running an atomizer that has a 2.5 ohm resistance at 4 volts will have the same regulator voltage drop as running a 3.7 ohm atty at 6V. It all boils down to how many amps you are drawing.

I think the TI chip I mentioned before will work very well for you. Plus, register at TI and have them send you some free samples. I think they limit it to 5 free samples. Thats what I did with the 5V fixed output LDO regulator.

 

[Nuck]

OK, now I understand what you ment by the voltage drop scaling with Vin. In the case of an atomizer or any fixed resistance load, this is correct. A 3.7 ohm atomizer running at 4V will put a 1.08 amp load on the regulator. The same atty at 6V will draw 1.62 amps. Running an atomizer that has a 2.5 ohm resistance at 4 volts will have the same regulator voltage drop as running a 3.7 ohm atty at 6V. It all boils down to how many amps you are drawing.

I think the TI chip I mentioned before will work very well for you. Plus, register at TI and have them send you some free samples. I think they limit it to 5 free samples. Thats what I did with the 5V fixed output LDO regulator.

I just checked out the UCC283-5 and the UCC283-ADJ. Both are excellent chips that will do exactly what I'm looking for. They are pricey though at digikey. At 9 bucks it adds quite a bit to the price of a mod but since I'm only building a few I think it's well worth it.

It's gonna be incredibly tight in the chrome body I'm using but I think I will try to add a switch that allows a bypass of the regulation. This will allow the use of 18650 as a power source for those days you just don't want the big heavy hits.

I did try to register at TI but for some reason the window just closes on me when I select Canada and try to register. Guess no love from TI

 

[Nuck]

Ok..the order is in for both of those chips. The adjustable comes in a 5 pin package. I got the info on the pins and the resistance values seem to be the same as the LM317 but I'm a bit confused on the resistor placement.

It looks like R2 is placed on the adjustment line which I assume goes to ground and the R1 is run between the ground pin and the adjustment pin.

Is this correct?

Edit: Nevermind, it appears to be identical to the LM317 with the addition of a reference ground.