mini adjustable voltage regulator

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http://www.instructables.com/id/Mini-Adjustable-Voltage-Regulator/

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Mini Adjustable Voltage Regulatorby MagicTKon October 15, 2014

Table of Contents

Mini Adjustable Voltage Regulator .................................................................................................

Intro: Mini Adjustable Voltage Regulator .........................................................................................

Step 1: Schematic and Battery Terminal Prep .....................................................................................

Step 2: Voltage Regulator Placement and Wiring to Voltmeter and Potentiometer ...........................................................

Step 3: Final Assembly and Epoxy ..............................................................................................

Step 4: Short video showing voltage changing .....................................................................................

File Downloads ...........................................................................................................

Related Instructables ........................................................................................................

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Comments ................................................................................................................
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Author:MagicTK

Electrical Engineer

Intro: Mini Adjustable Voltage RegulatorThe goal was to make a variable power supply and make it as compact as possible. This is what I made. I know there are many other voltage regulator projects out thbut I wanted to make mine to suit my needs. This instructable assumes you know how to solder and basic knowledge of how to align circuit components in a tightconfiguration. Let me know if you have questions, or try www.google.comfor help also.

The items listed below are what I used, or something similar. It isn't necessary to use exactly the same components that I have used, but I am giving you a few links th

might help. I also didn't use the capacitors like shown, because I only use it to power things temporarily, and typically don't care if there is some fluctuation.

Bill of Materials

Dual 9v battery terminal (this one is parallel connected, I need series connected, just to get higher voltage range, but if you only need up to 9v, then this wouldwork. If you can't find a series connected version, you can easily modify this one to be series) http://www.vetco.net/catalog/product_info.php?prod...If you use battery terminals like I've shown, you will need some prototype board, similar to this, but I highly recommend buying the dual terminals above becauit created more work to solder them properly:

http://www.mouser.com/ProductDetail/BusBoard-Proto...

Mini Digital Volt Meter https://www.adafruit.com/products/705A potentiometer with a knob, the LM350 recommends R2 = 5kohm along with the R1 = 240ohm, but I used R2 = 1000ohm and R1 was a 10-turn 20kohm pot ever rebuild this, I would definitely look for a physically smaller one, but still 10-turn, however this is what I had on hand). I show other potentiometers, but thoswere very high values like 500kohm and 2Mohm, they might have worked, I just chose not to use them.1000ohm resistor (if you use a 20kohm pot)LM350 3A Voltage RegulatorToggle Switch something like this is what I used:

https://www.superbrightleds.com/moreinfo/dimmers-a...

Small alligator clipsSome wireSolderHeat shrinkDuct tape or something to apply to the back of the volt meter as insulation (short circuits are usually bad)Epoxy (I used 5 minute type, but others could be used)

Note: If you use the dual battery terminal listed, then you would not need the PCB
https://www.superbrightleds.com/moreinfo/dimmers-and-switches/mini-onoff-toggle-switch/1353/https://www.adafruit.com/products/705http://www.mouser.com/ProductDetail/BusBoard-Prototype-Systems/SB400/?qs=sGAEpiMZZMtgbBHFKsFQgkU9HqdjFsiqUjQSFkmxBXQ%3dhttp://www.vetco.net/catalog/product_info.php?products_id=15055&gclid=CJbg8d6Gs8ECFcRzMgodQycALQhttp://www.google.com/http://member/MagicTK/http://member/MagicTK/


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Step 1:Schematic and Battery Terminal PrepFor the circuit, be sure you check the datasheet of whatever voltage regulator you are using. I chose the LM350 because it has higher current output, but I've usedLM317 in the past. If you plan to drive something with higher current needs, you might need a heat sink.

You will need to cut wires and cut open the plastic sheath around each battery terminal, if you use the individual 9v battery terminal with wires. If I were to build this agI would use the dual terminal type on the first page, and modify it to be series rather than parallel like that link shows.

Then you need to cut the prototype board to fit roughly the size of the two batteries together.

Solder the terminals onto the prototype board as shown, and add a short wire beneath the terminals on one end (as shown the red wire in the 4th picture). This will puthe batteries in series to give 18v, when you connect the other terminals. Keep track of which is +and -for correct operation.


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Step 2:Voltage Regulator Placement and Wiring to Voltmeter and PotentiometerI placed the voltage regulator on one edge so that I could bend the input terminal and make it stick through to the positive battery terminal. Then you just bend it to touthe terminal from the other side and heat it up and apply solder.

Then you cut the resistor shorter and bend one end around so it can be soldered to the regulator terminals as shown. I planned ahead and applied heat shrink tubingonce I had the wires soldered, but don't do it too soon unless you know where to make the next connections.

Refer to the schematic to understand where the volt meter needs to be connected. The red wire is the power for the meter itself, so I connected it to the 18v, and theblack wire to the ground point which will be after the switch.

I think I missed taking a few pictures for the rest of the wiring, but if you follow the schematic, you will see the battery ground is connected to one terminal of the switchthen another wire will connect to a terminal of the potentiometer (see yellow arrows on 6th picture).

Then the adjustterminal of the regulator will have a wire soldered to it which will go to the one terminal on the potentiometer. And the third terminal on the potentiomeis unused. Be sure you check that you have adjustable resistance. If you connect the two on the "ends" of the potentiometer, it will just be the max resistance and not the wiper. The potentiometer I used had its own schematic showing what each pin 1, 2, and 3 are.

The voltmeter black ground will connect to the same terminal of the switch that the potentiometer is, and the red positive wire will connect to the bent terminal of theregulator, which is the Input voltage. The white wire will connect to the Output of the regulator. I made each wire length fit to the distance and location of each connectkeeping enough slack to allow easy assembly.

Be sure you add duct tape or something as an insulator on the bottom of the voltmeter.


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Step 3:Final Assembly and EpoxyAt this point, all the wires should be soldered. You can carefully attach the batteries and turn on the switch and measure the voltage from the Output to the Ground

terminals and turn the potentiometer, the voltmeter reading should change.

If it makes it easier, solder some wire (see the silver wire) to the Ground terminal of the potentiometer and the other wire (copper) to the output of the voltage regulatoand solder the wire to the alligator clips (you might need to redo the heat shrink if you already did that earlier.

If this test was OK, then you can move on to epoxying everything together. No secret or best method, just hold the pieces where you want them to be, then find some of temporarily holding them together. I used Scotch tape and a Quick-Grip clamp or something, then applied some 5-minute epoxy with a toothpick and just waited untwas dry, then rotate the assembly and add more epoxy as needed to ensure it holds tight. Then remove the tape, clamp, or whatever temporary holding method youused.


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Step 4:Short video showing voltage changingThe minimum output is based on the voltage regulator's internal reference voltage (look at the datasheet formula), and the maximum output is based on the batteriesconnected and how much energy they have left (as well as the maximum specified in the datasheet, in case you connected much higher voltage).

Hope you enjoy making this.

File Downloads

Adjustable Voltage Regulator-1.m4v(7 MB)[NOTE: When saving, if you see .tmp as the file ext, rename it to 'Adjustable Voltage Regulator-1.m4v']

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Comments

10 comments Add Comment

victordoessays: Oct 21, 2014. 1:27 AM REPThis is really useful! Where going to buy a couple. but now thanks to you I can make them instead! Thanks

ac-dcsays: Oct 21, 2014. 11:33 AM REPKeep in mind that once you factor for the time and expense of buying the individual components, plus gas to drive to get them or shipping, it actuallyends up cheaper to just buy one ready made off eBay if you can wait a few weeks for it to ship from Hong Kong or another oriental address.

techlvsays: Oct 21, 2014. 8:36 AM REPRemember, the higher the voltage drop between input and output, more heat will be dissipated in the LM350. A heat sink may be needed in that case.

ac-dcsays: Oct 21, 2014. 11:31 AM REPIndeed. Voltage drop x current = watts. If it is approaching 1W or more there should be a heatsink on it.

MagicTKsays: Oct 20, 2014. 4:55 PM REPThanks. My first one, I had a SPDT switch and used a 7805 and 7812 for 5v and 12v but they were just fixed voltages. I wanted adjustable, and even had aseparate box to do that, but it still didn't make me happy because I always had to get my separate voltmeter to measure the output. So I added the voltmetdisplay. And other than the monstrous potentiometer (comparatively) it's a very compact design.

ac-dcsays: Oct 21, 2014. 11:30 AM REPLM7805 and 7812 aren't really/necessarily fixed voltage. I mean that they are the same as LM350 and others to the extent that if you vary the resistancto ground with a voltage divider (pair of resistors or one being a potentiometer as shown) subcircuit (just like with the other linears) you can adjust theoutput voltage.

3366carlossays: Oct 20, 2014. 7:06 PM REPThanks, I really like those voltmeters and plan to buy a few. btw, your movie doesn't work. thanks.

MagicTKsays: Oct 20, 2014. 8:43 PM REPI'll look into the video not playing. It plays on my phone and my computer, though. You might have to download it rather than play direct, then play it froyour device. Anyway, it was just a video showing me turning the potentiometer and the voltage increasing. And I'm glad you like this.

ibenkossays: Oct 20, 2014. 4:18 PM REPReally smart idea! Im going to make this! :)

seamstersays: Oct 20, 2014. 2:16 PM REPNicely done. Thanks for sharing this!
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