Wednesday, September 25, 2013

Dual Power Supply

Good evening everyone. Hope everyone is okay. This post is about dual power supply. 

Now if you are into hobby electronics projects and tech stuffs you may have come across the idea of dual power supply. You might have seen that Op-Amp requires Dual Power supply. In different power supply labels you may have seen powers like +12V, 0V, -12V or something like that. This post will help you to make one for yourself.

When I was a kid my brother got a remote controlled vehicle which can go back and forth. And as usual we opened it up and found an interesting motor feeding system. Though the vehicle was running from 4 AA size battery but only 3V was given to the motor, either from 2 of the battery or from the other 2. Thus achieving a different polarity causes it's direction to be different. It was about 11 years ago. Anyway don't want to bother you anymore with uninteresting history. Let's see the first figure.

This is how dual power supplies work. You can use any of these three points for getting different voltage level. 

From Battery

First, let's see how to make a dual power supply from battery. You can use any type of battery. For example you can use 4AA battery or 2 9V battery.

Very simple, right? Just connect both the battery in series. Now the center of the two cells will work as the Ground, and two other terminals will provide positive or negative supply. 

Very simple but effective. If you use two 9 volt battery you will get 9V 0V -9V power supply. With that you can power up small op amp IC or maybe small motor that will go in both direction.

Dual Power Supply From Battery


From CT Transformer

Okay now let's see how to make a dual or negative power from a center tapped transformer. 

Unregulated Dual power supply from CT Transformer

Regulated Dual Power Supply from CT Transformer

Voltage Testing

Voltage Testing

Diagram above is a diagram of Dual power supply capable of providing 15V-0V-15V. You can read my earlier posts to find out more about how this circuit is converting AC from DC, what is voltage regulation etc. Those posts may help you to understand this circuit better. Now for simplicity I will describe it in brief. First the transformer steps down the power to a lower level. Here it is 18V. And then the diode IN4007 converts it's to DC. Adjacent capacitors smoothen the power - Lowers the voltage ripple and noise. You have already got the dual power supply. But it's around 15V 0V -15V. And it's not regulated (1st diagram). To regulate it to 12V we will need one positive regulator and one negative regulator. 7812 is a positive regulator where 7912 is a negative regulator both 12V and 1A capable. At the Output side you will get +12V 0V -12V power(2nd diagram).

Actual picture doesn't have the regulator added to it, yet. If you add a regulator you will get a cleaner voltage, that means less noise and ripple. Open pictures to see them in high resolution. You will be able to see diode orientation and polarity from voltages from this. I needed three multimeter but I only have one working right now, two of my meters got busted. But still you can see that positive from one point and negative from another. If we use only positive and negative point, we would have seen around 44V here.

From ATX Power Supply

Now, I'm going to show one more way. Most of us have seen computer power supplies. Small but efficient and powerful. ATX power supplies provide both positive 12V and negative 12V.

A Corsair CX750 Unit, Colors refer to Wire color and respective voltage

Voltage of Blue Wire Respect With Ground/Black Wire
Voltage of Yellow Wire Respect With the Ground/Black Wire
This is how you can get dual power supply from your ATX power supply. Simple keep the power supply turned on. Click here to see how. Anyway as you can see form the ratings Blue Wire provides -12V, Yellow provides 12V and black provides 0V. As we can see from the same 0V respect we are getting 12V both positive and negative, we can obviously use it as dual power supply.

You can also check your own power supply to see the ratings. You will see the Yellow wire is for 12V, Black wire is for 0V and Blue wire is for -12V. You can use Yellow - Black - Blue configuration to get +12V 0V -12V supply. Though most power supplies -12V will provide only a small amount of current. But that should be okay for running most of the small ICs. If your power supplies cables are not color coded you can always use a multimeter to measure the voltages.

Anyways these are the three basic ways to get dual power supply. Hope it will help. Will update as soon as possible. 

You can visit the index for more interesting posts. 


1. If you use the CT transformer or ATX Power supply, Take proper caution from shock hazard.

2. Don't touch the circuit of a running ATX power supply.

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