Hi folks, I am trying to do an op amp experiment. As we all know, the op amp needs +15v and -15v. I have a really old school dc power supply similar to the one shown below. How could I get +15v and -15v at the same time out of this power that I have?
Thank you for your replies!!

 

As we all know, the op amp needs +15v and -15v.

No we don't all know that because it isn't true. Some opamps are optimized for operation from a single supply and I can't think of any "dual supply" opamp that can't be operated from a single supply.

I have a really old school dc power supply similar to the one shown below. How could I get +15v and -15v at the same time out of this power that I have?

Use a switching supply to generate a negative voltage. Supplement the existing supply with another 15V; isolated of course.

 

For experiments, two 9V batteries should suffice. Connect + of one to - of the other. That connection is the ground, the other two free connections are +9 and -9.

Bob

 

How could I get +15v and -15v at the same time out of this power that I have?

I downloaded the schematic:

It would be straightforward to add a negative supply that tracks the positive supply. Add two rectifier diodes and a cap or three, an opamp, a darlington transistor, a handful of resistors, and a banana jack.

 

It might be a better idea to build your own. Since you don't need a lot of current, it should be fairly easy. Tons of designs can be found with goo-fu. First hit on "bipolar power supply 15V design":

 

Can you scavenge an old computer power supply?

 

How could I get +15v and -15v at the same time out of this power that I have?

In the spirit of proposing solutions that satisfy the restrictions placed on solution space, here is my take at adding -15V to the existing supply, this is what I had in mind in post #4:

It does require adding hardware to the existing power supply, but it doesn't require adding another supply, or building a new supply from scratch.

The circuitry that isn't highlighted represents the existing circuitry. LM358 can be used for the opamp as long as you take into consideration maximum operating voltage. Output voltage is only guaranteed to be within a few volts of V+, so for tracking output near 0V, V+ for the opamp should be at least 3V. If the filtered DC peak is actually 27V, you'd be at the ragged edge of LM358 capability. You could use a couple zener diodes to bracked bracket the voltage range needed to generate 0V to -15V range. There are no issues with common mode input range or minimum output voltage.

Not shown is the jack for the negative voltage. There is no current limiting for the negative supply, but it will track the positive supply if it becomes current limited.

 

Thank you everyone for your replies. My project worked put very well with your feedbacks.

 

My project worked put very well with your feedbacks.

Glad it worked out.

What did you end up doing for a negative supply?

 

Can you scavenge an old computer power supply?

Some older pre ATX ones had a minus 12V output for early RAM chips and RS232.

You usually have to load the 5V output to get the PWM chip humming.

Its normally done with a 7912, so 1A limit on the negative output.