120Vac to +/- 12Vdc

[rekent]

I have a 3 prong plug going into an American wall outlet and need to convert that voltage to a buffered positive and negative 12 volts for use in a circuit. I am an early EE student and understand slightly beyond the basics of electronics design, but the details of dealing with AC power still elude me.

Any suggestions on how I might achieve this task? 120Vac to buffered +/- 12Vdc?

 

[crutschow]

You need a 120V transformer with two 12V or a center-tapped 24V output winding, two bridge rectifiers and capacitor filters to generate unregulated DC, and then two regulators to provide the 12VDC (such as an LM317 if you current is no more than an ampere or so per output).

What is the current you need?

 

[rekent]

Anyway you could possibly post a quick schematic of that please?

My maximum current draw is 500mA.

 

[crutschow]

Since you are a student it would be a good learning exercise for you to generate a schematic and have us critique it. You won't learn much if we spoon feed you the answer. Google what you need to know such as this on power supplies. Also Google about the 317 regulator.

The trick to being a designer is not knowing everything but knowing where to find everything.

 

[MikeMl]

Another valuable engineering skill; throw money at it Buy two of these.

 

[rekent]

Since you are a student...

Yes it would be a nice learning exercise, however I am only a sophomore (i.e. Gen Ed and basics only). We have not discussed transformers in any form, and I am at a slight loss as to which diodes would be best for the rectifier and what you mean by a capacitor filter. Perhaps with a little more assistance/leading I will be able to develop a schematic.

Another valuable engineering skill; throw money at it Buy two of these.

Buying two of those would not be very beneficial since I already said I have to go off a standard 3 prong 120Vac plug.

 

[MikeMl]

...
Buying two of those would not be very beneficial since I already said I have to go off a standard 3 prong 120Vac plug.

So you cant also buy**broken link removed**?

 

[rekent]

Ok let me explain this slightly farther. I am using a plug such as this one because of the small space where the male end of the cable must plug in (a wall adapter like the one posted would not fit in the space). I also have to use this type of power plug to make it more uniform, able to be powered with any one of the hundreds of these style power cords lying around.

 

[MikeMl]

I sure hope you are not using the pictured plug as an OUTLET. That would not pass UL/CSA certification; having exposed 120V on the prong is not allowed.

 

[rekent]

I sure hope you are not using the pictured plug as an OUTLET. That would not pass UL/CSA certification; having exposed 120V on the prong is not allowed.

I am using the plug in the same sense as you see on the back side of virtually every computer tower made.

 

[MikeMl]

Ok, so you are trying to build a custom power supply in your own enclosure which has a single pigtail power cord of the type you pictured?

You can still get two of the switching power supplies, strip off the plastic, and mount them in your enclosure, add line cord, fuse, and output connector of your choice.

 

[Reloadron]

Simple dual power supply that allows for adjustable outputs. If you don't want adjustable then replace the regulators with a LM7812 and LM7912 for fixed +/- 12 volt outputs. Look at the drawing and get the idea.

Ron

 

[arunb]

dont start on SMPS if you are a beginner, they could be complicated, a transformer based design may be easier to learn.