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Commentator

Join Date: Nov 2006
Posts: 60

# Powering Op Amp +/- 15 Volt

01/16/2007 11:33 PM

I would like to know is there a simple circuit to generate +15 and -15 volt from a single power supply to powering up an Op Amp 471. Can anybody help me. Thanks.

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Anonymous Poster
#1

### Re: Powering Op Amp +/- 15 Volt

01/16/2007 11:59 PM

There are a few ways I can think of to do this. First and maybe the easiest would be to use a virtual ground. You can use a 30 V power supply and create a virtual ground at 15 volts so your op amp would see the 30 volts as +15, the 15 volts as GND and the 0 volts as -15. One problem of this is both the input and the output will be mapped to this voltage transformation. You could also use a rail to rail op amp and just go from 0 to +V and not worry about not having a -V. Another method and more complicated is to make a DC-DC converter. There are converters that can change + voltage to - voltage. Look at the linear web site or national web site for application notes how to do this.

Commentator

Join Date: Nov 2006
Posts: 60
#2
In reply to #1

### Re: Powering Op Amp +/- 15 Volt

01/17/2007 12:19 AM

is there any circuit that i can refer to.

Anonymous Poster
#4
In reply to #2

### Re: Powering Op Amp +/- 15 Volt

01/18/2007 1:23 AM

Page 8 of http://www.national.com/an/AN/AN-69.pdf for the virtual ground. You can also look at national's web site for the switching regulators. Depending on your experience it can be easy or really hard to make these things. The do have tones of App notes to look at to make this stuff. Take a look.

Anonymous Poster
#5
In reply to #4

### Re: Powering Op Amp +/- 15 Volt

01/18/2007 1:27 AM

Oops, did I say page 8, I meant 6. Sorry.

Anonymous Poster
#6
In reply to #5

### Re: Powering Op Amp +/- 15 Volt

01/18/2007 2:45 AM

Its a good circuit, But my idea is we can use two resistor of same value with high wattage capacity accross the two capacitor and connected to supply and GND(Voltage Divider) instead of LM380. i dont know it will work or not but it is almost same like this circuit.

Thank you,

K.P.mahalingam,

Electrical and electronics engineer,

India.

Anonymous Poster
#7
In reply to #6

### Re: Powering Op Amp +/- 15 Volt

01/18/2007 10:18 AM

It all depends on the circuit but the advantage of using the op amp is the impedance to the virtual ground is very low. If you just use a resistor divider then the impedance will be the impedance of your resistors. If you were going to only use the resistors I would put a few capacitors across them so you will have a resistor and capacitor in parallel in series with another resistor and capacitor. It is even a good idea to put a capacitor across half of the trim resistor as in the applications note.

Anonymous Poster
#8
In reply to #2

### Re: Powering Op Amp +/- 15 Volt

01/18/2007 12:04 PM

You also can use an isolated DC/DC converter. I have used the ones form TI that seems to work pretty well. They are part number DCP01B series converters. You can look at the data sheet at http://focus.ti.com/lit/ds/symlink/dcp012415db.pdf . There is a dual output version too so get that one. You can even order a free sample of the dip package if you want to try them out. That's at http://focus.ti.com/docs/prod/folders/print/dcp012415db.html . This is not a bad way to do it either. How much power do you need?

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#3

### Re: Powering Op Amp +/- 15 Volt

01/17/2007 8:22 AM

Better use 7815 (+VE output) and 7915(-VE output) voltage regulator ICS

if you go through he google.com you may get this ICS data sheet. its very cheap and simple simple then other circuits.

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#9

### Re: Powering Op Amp +/- 15 Volt

01/18/2007 3:43 PM

Try this:

Part Total Qty. Description Substitutions C1, C2 2 2200uF 35V Electrolytic Capacitor C3, C4, C5, C7 4 1uF 35V Electrolytic Capacitor C6, C8 2 100uF 35V Electrolytic Capacitor R1, R4 2 5K Pot R2, R3 2 240 Ohm 1/4 W Resistor BR1 1 2A 30V Bridge Rectifier U1 1 LM317 Adjustable Positive Regulator U2 1 LM337 Adjustable Negative Regulator T1 1 30V Center Tapped 2 Amp Transformer S1 1 SPST 2 Amp Switch MISC 1 Heatsinks For U1 And U2, Line Cord, Case, Knobs For Pots, Wire

Notes

1. Since this project operates from 120 (or 220, or 240, etc.) volts AC, it MUST be built inside a case.

2. U1 and U2 get quite hot and will require heatsinks. A fan is usually not needed.

3. You can, of course, add a volt and amp meter.

4. U1 and U2 can only go down to a minimum of +-1.2V. If you need to go lower, you can add two 1N4003 diodes in series with the output of the regulator. The diodes drop about 0.6V each, which will allow the supply to go to 0. Note that this will also decrease your maximum output voltage by 1.2V. (Thanks to Steve Horvath for the suggestion).

I hope it help. I should be no more than 40USDlls.

Saludos!

Delmar

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#10
In reply to #9

### Re: Powering Op Amp +/- 15 Volt

01/19/2007 12:33 AM

The circuit Ahuev23 has posted will definitely do the job. If however you can cope with not being able to adjust the voltages then using 7815 +15 V and 7915 -15 V regulators will reduce the number of components and cost.

It all depends on what you wish to do. If you think you can use the power supply in various places for multiple applications then use the variable output regulators, but if it is a one off then the fixed regulators would more than likely be the best way to go.

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#11
In reply to #10

### Re: Powering Op Amp +/- 15 Volt

01/19/2007 11:40 AM

Good point Masu!!

If the power supply will be used just for this project is better fixed regulators!.

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#12

### Re: Powering Op Amp +/- 15 Volt

01/20/2007 12:03 AM

Jusat find out a single to dual supply converter IC or if your supply is using Split-transformer [15+15V & 2 diodes] then simply connect a bridge rectifier across 30VAC & get O/Ps from (+) & (-) points of bridge; while centre-tap as common [as is being used by you normally].

Enjoy