Introduction: Advanced Adjustable Dual Mode DC Voltage Regulator

Picture of Advanced Adjustable Dual Mode DC Voltage Regulator

Got projects to work on and don't have a voltage regulator? Here a simple yet efficient DC voltage regulator. Its simple in design, yet efficient in output, but still cheap for your pocket. Key features;

--> Adjustable positive DC voltage regulator for all most powering up any circuits

--> Adjustable negative DC voltage regulator for op-amps & amplifiers.

--> A USB fast charger for your phone

--> A USB port to power up your microcontrollers Arduino etc.

This is my first instructable, so there might be a lot of missing here and there. Just let me know about it what's missing and I'll update.

Step 1: The Concept & Design

Picture of The Concept & Design

The Concept

Beyond, I present you the most advance yet the cheapest Adjustable DC Voltage Regulator. Yay! but wait there are 100 instructables in 'instructables' so what so special with this.

The main concept of the DC voltage regulator was to:

1: (1V to 35V) Adjustable Positive DC Voltage.

2:( -1V to -35V) Adjustable Negative DC voltage.

3: A fast charger for mobile phone & a USB power source for Arduino.

4: Simple and easy design within a cheapest budget.

The maximum output current is 1.5 A.

The Design

The material design pattern was to minimize the size & price of the product while recycling most hardware parts as possible by reusing the components obtained from the worn out electronics junks. I concept design was able made practical up to a limit by using the body of a burn out SMPS(power unit in Desktop Computers) and the capacitors which are de-solderd from the board.

The circuit design was adopted from the datasheets of the respective ICs. The PCB layout was design on those schematics with protection diodes to keep circuits protected from short-circuiting while connecting across output.

For the positive DC voltage regulator LM317 IC with maximum output current of 1.5 A is used.

For the negative DC voltage regulator LM337 IC with maximum output current of 1.5 A is used.

And finally for the for the USB charger 7805 with maximum output current of 1.5 A is used.

Step 2: Step:1 Gather the Components.

Picture of Step:1 Gather the Components.

The main point of DIY project within a budget is to choose your components wisely without a compromise in the efficiency. The idea as such as it is implemented in my project. Many of the components used are of cheap yet high in efficiency. Here is the list of components;

1: Transformer 15V (15-0-15) 2Ampere x 1

2: Capacitors:

i) 2200uF 50V x 2

ii) 10uF 50v x3

iii) 0.1uF x2

iv) 22uF x1

3: Resistance

i) 120 ohm x1

ii) 240 ohm x 1


i) LM 317 x1

ii) LM 337 x1

iii) 7805 x1

5: Potentiomete 5Kohm(max) x 2

6: Diod IN4007 x 8nos

7: LED (different colours) x2

8: Switches

9:Standerd USB port (female) x1

For etching the PCB

HCL (Hydrochloric Acid)

Hydrogen peroxide (Solution)

Aceton (Nail Polish Remover)

Copper Clad

(The session about how to etch a PCB is not covered in here, I guess there are better authors on that topic is in here. Anyway sooner or later I will write an instructable about it. )

Now if you want to test the circuit for yourslef you might need the following components too;


Bread Board


Jumper Wires

Cutter & wire stripper

Tips And Tricks

Many of the capacitors used in this project are available from the worn or burn out SMPS board. So if you've a worn out board, try desoldering the components. This not only yu yusaves you money but also helps to save our nature from the E-Waste threat.

Step 3: About the Circuit (A Very Very Very Brief Overall Explanation of Circuit)

Picture of About the Circuit (A Very Very Very Brief Overall Explanation of Circuit)

The main functional part of the regulator are the ICs. They ICs regulate the the output from the capacitors C1 and C2 which is actually full of ripples to a steady DC output.

The positive voltage regulator LM317;

The diode D1, D2, D3, D4 regulates the Sin wave obtained from the transformer into respective half waves of positive and negative halfs. The capacitor C1 and C3 takes in the positive half of the sin wave and converts in short of DC output by continuous charge and discharge pattern. Yet it is not a complete DC output as it consists of some of the sin wave pattern created due to the time gap between the charging and discharging process called the ripple factor. The LM317 takes in those ripple factor contained waves and attenuates the ripple to give a steady DC output voltage.

Likewise the rippled output from the capacitors of negative voltage is taken in by the IC LM337 and attenuates the ripple factor to give a steady negative output voltage

The 7805 limits the input voltage to a 5V output.

All of these ICs give a maximum output current upto 1.5 A.

The extra diode across the input and output of LM317 and Lm337 are called protection diode, they are necessary as it prevents the ICs from damaging under extreme conditions. The didoes across the output and adjust keeps the diode protected from the short circuiting problems.

The capacitors C7,C8 attached at the output reduce the ripple readings from the diode.

To know more detailed information about the circuit and 'why' and 'where' of the components, take a look at the IC datasheet attached.

Step 4: Step 2: Lets Create the PCB

Picture of Step 2: Lets Create the PCB

Now to the main step, with the given design attached as pdf etch the PCB. Make sure all the lines are clear and connected. As I mentioned earlier I'm not going through the entire process of etching a PCB. Unlike the myths ever told ;) its actually easy to etch a PCB! To know more about it try searching in instructable about "How to etch a PCB".

The PCB for power supply and USB are made separately. Just follow the top view to

Follow the top view diagram to solder the components easily.

Make sure the polarity of diodes, capacitors and the ICs are correct. If not you might end up with a blown capacitor or burn out /overheated ICs.

Also never ever reverse the polarity of USB male port! Make several rounds to make sure the connections are right.


A left to right rotatory motion on potentiometer is ideal for the "Increment of the voltage", inorder to attain that ,test the output ports say pin1,pin2 & pin3 of the potentiometer across a multimeter to find out which gives an increment of resistance.


Find out which two pins pin1 & pin2 or pin2 & pin3 and attach the corresponding pins to adjust( always the middle pin,pin2) & ground (pin1 or pin3- depends on your theory).

Step 5: Step 3: Screw Them, Tight Them & Finish It Up

Picture of Step 3: Screw Them, Tight Them & Finish It Up

Now its time to finish the project. So hey, what to do with the switches? Well, just follow the instructions.

The box of the power supply is a metal body of the recycled SMPS. The front panel has been removed and attached with a cardboard with appropriate holes and spaces for switches, minivoltmeter & USB port. The external connection are as follows

1: Connect the DC power lines to the screw switches both the positive and negative lines but not the ground wire, well not yet.

2: Connect the ground from the Transformer to the switch 1, now from the switch (the second port) to the PCB.

3: Attach a 470 ohm resistance to the power line from the " To LED " on the PCB, then to the anode of a Red LED. and the cathode to the ground line on the PCB.

4: Get another set of wire from the Transformer,connect the line to the input of Switch 2, from the other port of switch to the input of 7805. Finally connect the ground wire.

5: For the voltmeter connect the Red wire across the positive DC output terminal and the ground output terminal.

6: To place the USB port tighten just bend the side arms to both sides of the board sheet.

Step 6: What Might Go Wrong & How to Solve It!

Picture of What Might Go Wrong & How to Solve It!

Here the list that might go wrong with the project and how to solve it;

1: Usually there might be a confusion with the polarity of the USB port.

Inorder to test the USB port you might need a USB cable with its other end open exposed to 4 wires. Connect an LED's anode across the Red wire and cathode across the Black. If lighten up the connections all clear. Remember to add a resistance before connecting it directly. Refer the attached diagrammatic representation.

2: Fluctuations at the output.

Its quite normal to obtain a +0.01 /-0.01 voltage variations at the output. If the rate of fluctuations aren't within the limit check the last capacitor C7 & C8.

Sometimes a burnt potentiometer would also create a fluctuated output. Check the potentiometer too.

3: The minivoltmeter does not showing voltage reading below 4V.

For some voltmeter such as the one shown in picture the minimum reading that can be obtained from the voltmeter is 4v, so below the 4v the reading can be only obtained by a multimeter.

4: How to obtain a negative reading across the mini voltmeter?

Actually I cant ,the rage of reading for the mini voltmeter used is between 4v - 100v, if you have an alternative choice go for it. Otherwise just measure with the multimeter.

Remember to connect to the ports mentioned in diagram.

Still got any doubts & complaints fell free to ask in comments.


About This Instructable




Bio: Hey I'm Matthew, you can call me Mathz. I'm 20, and currently studing for Electronics and computer hardware.I belive in the best ... More »
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