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Offline SolarRay

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Enable LDO's and Touch Sensor
« on: April 15, 2012, 05:25:17 AM »
There are a number on “Enabled” adjustable LDO’s on the market with high output current.  These can make decent voltage regulators for PV mods providing adjustment between 3.5V and 6.5 volts, current up to 7 amps using two 3.7volt batteries.
 
What is an “Enabled” LDO? It has a Enable pin that turns on the LDO. This pin requires a 5 volt logic signal at just a few hundred micro amps typical to enable the LDO.
 
In the circuit posted we are using a “Master switch” such as a tail-cap found on flashlights  or other user installed switch.

In the posted circuit using a Touch activated circuit as the “Fire” button.  The PNP Darlington pair transistor is the switch mechanism. Darlington pair transistors are very high gain devices so it take very little base current to activate them. (the base is connected to R4 in the posted circuit)
R5 and a 4.7 volt zener diode make up bring the the logic signal to the correct voltage and current levels.
The rest of the circuit is standard typical style for most voltage regulators. The Values for C1 and C2 are recommended by the manufacturer.
R1, R2 and R3 provide the voltage adjustment as per manufacturer
R4 would normal be in the neighborhood of 100K
R5 and the Zener Diode  can be calculated using the handy calculator:

Zener Diode Power Rating Calculator

Some of the Enabled LDO require only 200 micro Amps on the 5 Volt enable signal.
So I was wondering do we need the Darlington Pair at all?
Skin is 100,000 ohms per Square Centimeter
100K resistor + 100K skin = 200K Ohm 8V divided by 200K Ohm = 0.00004 = 40 micro amps
So the answer is Yes but we only seem to need a gain of about 5x……. 40 * 5 = 200
I would imagine we need the Darlington Pair to ensure reliable operation.

Anyone have any thoughts or input?
I will post some part numbers for Enable LDO’s on my next post
« Last Edit: April 15, 2012, 05:28:59 AM by SolarRay »

Offline SolarRay

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Re: Enable LDO's and Touch Sensor
« Reply #1 on: April 15, 2012, 02:57:09 PM »
New schematic. The above schematic is incorrect. Here is a corrected schematic. The touch sensor now goes to ground, which is the correct configuration for a pnp transistor and much better for metal cases, flash light mods and tube mods that use the case as ground.

Enabled LDO with High Current Output, Adjustable and Vin 8v or more:
EXAR SPX29501/02
MICREL 29302,29502 29752
On Semi NCP5663 NCV5663 NCP 59300
« Last Edit: April 15, 2012, 03:21:01 PM by SolarRay »

Offline CraigHB

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Re: Enable LDO's and Touch Sensor
« Reply #2 on: April 15, 2012, 03:52:59 PM »
You could probably use a Darlington pair if you really wanted, but a MOSFET will do a better job cheaper with fewer components.  I don't know how well a Darlington pair would work myself since I've never tried it.  The best solution is to use a capacitive touch sensor.  Single channel controllers are sort of uncommon, but there's a few out there.  Atmel makes a good one.  Some MCUs have a built-in touch sensor function which is handy.

You can use the converter controller's enable pin as a master switch, but the problem is there is always some quiescent draw even with the regulator in shutdown mode.  It varies so you'd have to reference the data sheet for the particular switching controller.  Better to just use a P-channel MOSFET to switch converter power and tie off the enable pin.  For a boost converter, there's no option since boost controllers can not disable input current (due to their architecture).
« Last Edit: April 15, 2012, 03:57:07 PM by CraigHB »

Offline SolarRay

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Re: Enable LDO's and Touch Sensor
« Reply #3 on: April 15, 2012, 05:14:09 PM »
Craig, thanks for the input.

We don't want to use an MCU here, this design is to be ultra simple.
The design is also trying to get away from the high power MOSFET, I know that technique works well; however it is a little bulky.
Since we are driving the enable pin on the LDO it takes a very small signal so it possible to use 1/8 watt resistors and diodes and transistor. 

We also trying to eliminate a 3 amp push button. Which is also kind of bulky and tends to run about $2.00  to $3.00 which is more than the resistors, diode, and transistor.

Darlington pair can be built from two common pnp transistors as well.

Plus touch sensors are cool!
« Last Edit: April 15, 2012, 11:37:48 PM by SolarRay »

Offline SolarRay

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Re: Enable LDO's and Touch Sensor
« Reply #4 on: April 15, 2012, 11:31:39 PM »
Initial test show this is works well. I don't have an Enabled LDO to play with yet, but I am lighting up an LED with this circuit. The Resistor values will have to played with to get it to work just right.

 I found that a 1 Mega Ohm resistor from Ground to Zener / R5 junction seems to shut down everything pretty quickly. Circuit use about 1 micro amp when the touch circuit is not engaged,  it may use more when then LDO is deployed. The master switch is essential to ensure its not firing up when you don't want it to and save battery from the any  (albeit very minimal) power draw.

I can't wait to put this into a mod.

Offline SolarRay

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Re: Enabled LDO's and Touch Sensor
« Reply #5 on: April 19, 2012, 12:47:18 AM »
Bread board test results.

So I got an Exar and Micrel 29502 LDO's in the mail today. each was about $5.00 each one is rated for 5 amps.  (hey that's a dollar per amp). The proposed touch circuit using a Darlington pair PNP transistor works FANTASTIC . Fast response to finger (dry). All the resistors can be 1/8th watt size. The zener diode is rated for  1 watt but is no bigger than an 1/8 watt resistor. The caps I'm using are: a 16v, 6.8uF electrolytic  and a 16v, 22uF Tantalum. if you can find 10v caps they will be smaller in physical size. Current draw with SW1 on but touch NOT activated is less than 1 milli-amp.
Both LDO's are available in the smaller TO-263 size or the Standard TO-220 Size. C1 is not critical and can be left out.

You could defiantly build this whole circuit in a very small space, plus the fact there is no bulky FIRE switch. SW1 is designed to be a "Tail cap switch" but could be a  "Battery Removal" or other. .... If one was to go over to surface mount construction it could be REALLY tiny.  5 amp rated LDO's may be a bit over kill, could probably get away with the 3 amp rated versions, because e-cigs are usually have short ON times.

Final schematic will be posted next. (would have posted this time, but the cat jumped in my lap and hit the enter key prematurely).
« Last Edit: April 19, 2012, 01:47:02 AM by SolarRay »

Offline SolarRay

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Re: Enabled LDO's and Touch Sensor
« Reply #6 on: April 19, 2012, 01:05:21 AM »
Final Schematic:

with these resistor values and pot variable voltage yields 3.5 to 6.0 volts
« Last Edit: April 19, 2012, 01:17:59 AM by SolarRay »

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Re: Enable LDO's and Touch Sensor
« Reply #7 on: April 19, 2012, 02:06:48 AM »
You could probably use a Darlington pair if you really wanted, but a MOSFET will do a better job cheaper with fewer components. 

The Darlington Pair touch switch requires: 6 components, instead of 3 components required for MOSFET touch switch. That is only 3 more, but twice as many and requires an LDO VR with an Enable pin. I did see a boost driver with a logic level enable when browsing parts...I'll try and find it.

Cheaper? From my local surplus:
DARLINGTON = 4 resistors at 6 cents, 1 diode at 14 cents, and 1 Dar PNP transistor at 14 cents. = $0.52 cents

MOSFET (5 Amp to 15Amp)  $1.25 to $1.99

Online Breaktru

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Re: Enable LDO's and Touch Sensor
« Reply #8 on: April 19, 2012, 09:35:00 AM »
Thanks for sharing. It's nice to have another alternative for the touch circuit. Good work  :thumbsup:

Have you done any testing with 1.5 ohm or higher atty loads.
I have found that the mosfet circuit using a 1.5 ohm needed tweaking.
Being you are not breaking heavy current and using it on the enable (low current) pin, it may not be effected by the load.  :Thinking:

Offline SolarRay

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Re: Enable LDO's and Touch Sensor
« Reply #9 on: April 19, 2012, 02:22:34 PM »
Thanks for the Props!   :D, So many people have done fantastic work on this site. I would have never have gotten so far into modding without the Breaktru forum. I wish I had start vaping and modding long ago...I combines too of my favorite things: Electronics and Vaping.

I didn't see anything wrong with the original touch switch, just wanted to to provide an alternative....being mostly a digital guy...something using a digital logic level. The same logic level can also be used to activate other logic circuits in parallel....such as a tiny MCU like the microchip 12F675, (the surface mount is about the size 1/16" x 3/32"...which can be use to drive LED's....for those who want a crazy light show (search google: "12F675 RGB driver" which can be hacked to do away with the drive transistors and drive LED's directly at up to 10ma - 15ma, not as bright, but still cool)....or as a voltage meter via LED's.....similar to a bar graph....Not nearly as cool as a fully controlled MCU mod with display, but a mid level complexity project....I've seen the surface mount chip programed via a special socket or by soldering wire wrap wire to the pins and then connecting via clips.

Craig is correct that Capacitive touch switches with MCU's is usually the best way to go...However, this method opens up using programmed MCU's (available from the web) or hacked from greeting card, lighted shirt buttons, etc ....that require a logic level (high) to activate....if they require a LOW to activate as simple transistor based logic inverter can branched off..You could also use a physical switch to activate as well. (I wanted to get away from physical switches because they do wear out, common place in mods, take up lots of space, and are one of the more expensive parts). Sometimes the "Gotcha" is that they (the MCU's from other sources) are looking for a button quick press, not a "held" state. You have have to provide an 3.3 VR but there is a surface mount ones in SOT23 packages that are about the size of grain of rice. You can "free form" build surface mount but it's somewhat a "B**CH", you can also mount some of it on protoboards using superglue, solder and wire wrap wire for connections.


 Hope this post sparks some creative ideas for you Modders out there. :rockin smiley:

Here is one more contribution, a build plan for "free form" construction:
« Last Edit: April 19, 2012, 02:34:43 PM by SolarRay »

Offline SolarRay

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Re: Enable LDO's and Touch Sensor
« Reply #10 on: April 19, 2012, 02:24:38 PM »
Have you done any testing with 1.5 ohm or higher atty loads.
I have found that the mosfet circuit using a 1.5 ohm needed tweaking.
Being you are not breaking heavy current and using it on the enable (low current) pin, it may not be effected by the load.  :Thinking:

Not yet....Once I get it built in to a fully working Mod I'll test it with some 1.5 Ohm atty's and some Dual coils at my local vape lounge.

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Re: Enable LDO's and Touch Sensor
« Reply #11 on: April 19, 2012, 05:04:06 PM »
Cheaper? From my local surplus: DARLINGTON = 4 resistors at 6 cents, 1 diode at 14 cents, and 1 Dar PNP transistor at 14 cents. = $0.52 cents

You can implement that circuit with a small signal P-channel MOSFET and two resistors if active low, N-channel and 3 resistors if active high.  However, it's true that it would be more expensive to use a power MOSFET, but you're not doing that.  You're only driving an enable pin.

My argument before was that due to idle power consumption, it may be better to switch power to the converter with a power MOSFET than use the converter's enable pin, albeit a more expensive solution.

Offline SolarRay

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Re: Enable LDO's and Touch Sensor
« Reply #12 on: April 19, 2012, 09:03:29 PM »
Oh, I see what mean use a small signal MOSFET rather than the Darlington to drive the enable pin.  :facepalm:
Would would  we still need the 5v zener plus its' resistor to bring the signal to logic level?

Craig don't get me wrong, I think your work and suggestions are incredible, you are defiantly a GURU!

I wasn't trying to criticize the earlier suggestion, just bring my goals (cheap and easy) for doing it this way to light....




 

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Re: Enable LDO's and Touch Sensor
« Reply #13 on: April 20, 2012, 03:30:23 PM »
As far as logic levels, most regulators (converters) have a limit of -.3V to Vcc +.3V on logic inputs.  That may not always be the case, but usually it is.  Now if you were driving an MCU input, you may need level shifting since in that case, Vcc for an MCU would likely be regulated to a lower level.

In any case, there's always more than one way to do something in electronics.  Using a Darlington pair could very well be a better solution if it's a particular matter of cost and parts availablity.  I wouldn't say there's anything wrong with your solution.  It's definitely worth experimenting with and posting.  Though, it probably would not be the most traditional approach.

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Re: Enable LDO's and Touch Sensor
« Reply #14 on: April 20, 2012, 06:52:26 PM »
I guess I should learn more about MOSFETs,   :laughing: I've always thought of them as a "high power" switch. Often required for large load switching when a common transistor is not up to the job. I knew from school (long ago now) the darlington has a very high signal gain, and can take a very small signal such as the touch sensor and amplify it enough to be useful. And can be built from two common transistors which many people may have on hand. I guess the small signal MOSFET can do the same...definitely worth exploring and experimenting.  :Thinking:

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Re: Enable LDO's and Touch Sensor
« Reply #15 on: April 21, 2012, 05:58:11 PM »
Actually, there is one advantage to the Darlington pair.  It's much less sensitive to ESD or static discharge.  It's not impervious, but MOSFETs are highly delicate in that regard.  Though you can get MOSFETs with built-in  clamping diodes to achieve an amount ESD protection, probably about the same tolerance as the BE connection on a bipolar transistor.  You can also add a Zener externally on a MOSFET to provide ESD protection.

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Re: Enable LDO's and Touch Sensor
« Reply #16 on: April 22, 2012, 07:15:27 AM »
Cool thanks for the info.....I have a MOSFET for the circuit used in the Copper Side By Side, Although it is currently lost in parts storage bins.....I guess I should find it and  make SURE it is in an anti-static bag.

I have moved from breadboard to workbench with this Darlington circuit.... the Case (tube) is going to take a while but, the circuit is performing well....I should be able to take some test tokes from it tomorrow...its 90% built with the last 10% awaiting the case to be finished. I have hooked it up temporarily to make sure its correctly built and working and made initial measurements.  Built in free form to plan posted above. So far so good.  :thumbsup:

May design it as  a small circuit board for surface mount.  at 11 board mounted components it would be too extreme of a build as surface mount. I think I can get all 805's for the resistors, caps,  & diode. The transistor: SOT23 and the LDO: TO-263. I won't go smaller than 805....the 603's are too much of a fiddle.
« Last Edit: April 22, 2012, 07:18:58 AM by SolarRay »

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Re: Enable LDO's and Touch Sensor
« Reply #17 on: April 22, 2012, 10:08:41 AM »
Cool thanks for the info.....I have a MOSFET for the circuit used in the Copper Side By Side, Although it is currently lost in parts storage bins.....I guess I should find it and  make SURE it is in an anti-static bag.

I have moved from breadboard to workbench with this Darlington circuit.... the Case (tube) is going to take a while but, the circuit is performing well....I should be able to take some test tokes from it tomorrow...its 90% built with the last 10% awaiting the case to be finished. I have hooked it up temporarily to make sure its correctly built and working and made initial measurements.  Built in free form to plan posted above. So far so good.  :thumbsup:

May design it as  a small circuit board for surface mount.  at 11 board mounted components it would be too extreme of a build as surface mount. I think I can get all 805's for the resistors, caps,  & diode. The transistor: SOT23 and the LDO: TO-263. I won't go smaller than 805....the 603's are too much of a fiddle.


Can't wait to see the photos of the finished product.

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Re: Enable LDO's and Touch Sensor
« Reply #18 on: April 23, 2012, 04:31:30 AM »
Here some previews....

My Comments on my photos:

Photo 1: Dang how I am going shove all those electronics into that little tube  :wallbash:

Photo 2: Its looking kind of Steampunky right now, but Its going to get a coat of paint. Ready for final sanding cleaning and priming.

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Re: Enable LDO's and Touch Sensor
« Reply #19 on: April 25, 2012, 04:50:49 AM »
34 Guests browsing this topic? at 3 am on a Tuesday? Wow! :laughing:

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Re: Enable LDO's and Touch Sensor
« Reply #20 on: April 25, 2012, 07:32:16 AM »
Here some previews....

My Comments on my photos:

Photo 1: Dang how I am going shove all those electronics into that little tube  :wallbash:

Photo 2: Its looking kind of Steampunky right now, but Its going to get a coat of paint. Ready for final sanding cleaning and priming.


Very interesting concept.  :applaude:
I'm very curious to see what this ends up looking like  :popcorn:

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Re: Enable LDO's and Touch Sensor
« Reply #21 on: April 27, 2012, 04:40:49 AM »
Just shut down my workshop at 3:00 am (again).
Painting done: ( plus I got tired of wet sand, additional coat, wet sand, additional coat.... Repeat)
Fabrication: done (well one more small hole for the power LED, didn't know where it was going to go exactly till now)
Wiring and assembly: in progress...ONE more day should finish it!.....

been working my tail off trying to get er done. My JoyTec Egos work great but I need something that is adjustable and doesn't cut out after 10 seconds, other than my benchtop mod.

I have a Copper VV with Digi-pot 3/4 complete too! Mounting the two tiny tiny micro switches for the voltage up/down should be a new adventure in frustration  :wallbash: not to mention the tiny 3 amp fire switch I have for the Copper it's 4-40 threaded. Hopefully will have that mod done soon too! It's PTN4050C based.

Will post pics soon as either one is complete.  :)
« Last Edit: April 27, 2012, 04:44:30 AM by SolarRay »

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Re: Enable LDO's and Touch Sensor
« Reply #22 on: April 27, 2012, 03:28:03 PM »
I hate those short cutoffs.  I use a 30 second cutoff with my own mods. 

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Re: Enable LDO's and Touch Sensor
« Reply #23 on: April 28, 2012, 04:16:42 AM »

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Re: Enable LDO's and Touch Sensor
« Reply #24 on: May 04, 2012, 03:13:30 AM »
See above link for a performance report. Scroll down past the pictures. look for the post entitled update

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Re: Enable LDO's and Touch Sensor
« Reply #25 on: May 04, 2012, 09:37:28 AM »
Nice solar, good work.
I kinda got use to using the mosfets but may try a darlington one day.

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