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Improved Simple Adjustable DC Power Supply

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Improved Simple Adjustable DC Power Supply
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  http://www.instructables.com/id/Improved-Simple-Adjustable-DC-Power-Supply/  Food   Living   Outside   Play   Technology   Workshop Improved Simple Adjustable DC Power Supply by stuuf  on August 14, 2008 Table of Contents Improved Simple Adjustable DC Power Supply ........................................................................................1 Intro: Improved Simple Adjustable DC Power Supply ................................................................................2 Step 1: Parts and Tools ......................................................................................................2 Step 2: Circuit schematic .....................................................................................................3 Step 3: Mounting the power jack and regulator .....................................................................................3 Step 4: Installing other components .............................................................................................4 Step 5: How to use it ........................................................................................................5 Related Instructables ........................................................................................................5 Advertisements ...............................................................................................................6 Comments ................................................................................................................6  http://www.instructables.com/id/Improved-Simple-Adjustable-DC-Power-Supply/  Intro: Improved Simple Adjustable DC Power Supply Work in progress: I'll add more text explaining how this thing actually works and a schematic image in the next few days.There are already a few instructables about using linear voltage regulator chips to power low-voltage experiments and projects. This is my variation on those, using a lowdropout regulator to allow lower input voltages and a coarse/fine adjustment system. Image Notes 1. Voltage Regulator2. Input power3. Output power4. Coarse voltage control5. Fine voltage control6. o.O Step 1: Parts and Tools You will need the following components:LDO voltage regulator such as MC33269TO-220 heat sink and mounting screwCapacitors to filter the regulator's input and output circuits240 ohm resistorTwo potentiometers: 1Kohm or more for coarse adjustment, 100 ohm for fineI used trimmers for both pots, since they're compact and hard to accidentally adjustPower connectors: a PCB-mount coaxial jack for input and screw terminals for output are usually the easiest to work with3-4 square inches of perfboardSome hookup or bus wireYou should have these tools available:Soldering ironSmall screwdriverPliers and wire cuttersA sharp knife that can carve your perfboard such as a regular #11 X-ACTO blade. (or a 1/8 drill bit)  http://www.instructables.com/id/Improved-Simple-Adjustable-DC-Power-Supply/  Step 2: Circuit schematic Check the datasheet for your regulator for details about what capacitor values should be used and how to wire an adjustable regulator circuit. Instead of a single variableresistor to adjust the voltage, I added a second one for fine adjustment. With the two resistors in series, the voltage depends on the sum of the two, so adjusting the finecontrol (which has lower resistance) will change the output voltage slowly. Step 3: Mounting the power jack and regulator The most common style of DC power jacks uses two large pins that are too wide to fit in standard perfboard holes. To be able to mount the jack, you need to cut widerholes in the board. There is also a third terminal on the jack used for a switch. Since this circuit doesn't use that terminal, and since it gets in the way, you can bend it outof the way or cut it off.New method: I've also discovered that it's easier to just drill three holes with a 1/8 bit, widening the existing perforations.Medium- and high-power linear regulators use TO-220 packages that can be mounted to a heatsink to safely dissipate more heat. Heatsinks made for TO-220 devicesare usually a block of aluminum with a 4-40 threaded hole tapped near the top.  http://www.instructables.com/id/Improved-Simple-Adjustable-DC-Power-Supply/  Image Notes 1. I ended up cutting this tab completely off so i could run a piece of wireunder it without shorting Image Notes 1. This gray sheet is an insulator, so that the heatsink won't be electricallyconnected to the output voltage terminal. There's also a plastic ring under thescrew to keep it insulated from the tab. This is optional, of course. Step 4: Installing other components Mount the remaining components on the board and solder them together according to the schematic.

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