Hi Everyone,

Is there negative Voltage References?
I am looking for -2.5V Voltage Reference IC.
Can anybody recommand part number or brand of a product to me.

Best Regard

 

Ah, google must be down in Tawain, let me help you then:

http://focus.ti.com/docs/prod/folders/print/lm237.html

 

Ah, google must be down in Tawain, let me help you then:

http://focus.ti.com/docs/prod/folders/print/lm237.html

That's not a reference, it's a regulator. Regulators generally are not as precise or as stable as references. Also, references are not designed to carry significant current.

If you know how to use a zener as a negative reference, you can use a shunt reference IC (2 or 3 pin) the same way.
Series references (at least 3 pins) are generally positive output devices, but they can be used as negative references. See AN42 from Linear technology for some ideas.

 

How do you get a negative reference when all there is to work with is positive voltages

 

You can also use the TL431, connected in this way.

 

You can use a positive reference and a unity gain inverter.

 

You can also use the TL431, connected in this way.

That illustrates the point I made about knowing how to use zeners as negative references.

 

I suggest you Google this phrase negative voltage reference. Then select a few options. And take them back here for comments. Remember always to check availability and package type before you made your final design.

 

Too simple!

The TL431 circuit shows (+) power at ground and the (-) power feeding the circuit. That is not possible if you only have one positive supply to work with that has (-) at ground, like normal.

Look at the LM317/350/338 data sheets for making adjustable regulators. Their adjustable output starts at +1.25 volts. If you need to start at 0 volts, you need a negative voltage to supply -1.25 for the regulator which you can't get with a negative grounded supply.

So far, a small switching inverter like a MC34063 is as close as I can get to cheap, simple, compact reversed power.

 

Clearly, if there is no existing negative supply one would need to be created, either at the desired reference value, or a more negative value to allow for regulation.

Perhaps the OP merely had difficulty understanding that a typical shunt reference device can be used for either polarity, given suitable supply rails.

 

By the way. Why do you need a negative reference? Can your problem be solved with a common positive reference and a summing opamp configuration.