Hi all,

I need a stable -2.5 V on a negative power supply rail so I am looking for a fixed -2.5 V negative regulator (same as 7905 for -5 V ).
I found the LM2937-2.5 for positive 2.5 V, but I would need for a negative voltage output.

Can you suggest me if there is a LM2937-2.5 negative equivalent ?
Thank you in advance.

 

There is a LM337 negative equivalent to the LM317, so you can program -2.5V by selecting the resistors.

 

Try LM337 and adjust the output to 2.5V .

 

I know the LM337 but I would like to avoid to adjust the output with the external resistors and having problems with tolerances etc.
There is not a 'negative equivalent' for the LM2937 ?

 

You just using the pot to try and then using the fixed resistors to replace them.

 

I already mounted a trimmer on my breadboard as well, where I am doing some testing before making the PCB. It's not so trivial to set it to -2.5 V..
Maybe I have to try with 1 % resistors..

 

I already mounted a trimmer on my breadboard as well, where I am doing some testing before making the PCB. It's not so trivial to set it to -2.5 V..
Maybe I have to try with 1 % resistors..

Sometimes you need to using 1% and different value of resistors in series with them.

 

and different value of resistors in series with them.

That's why I would like to avoid putting resistors in series etc..

Actually, from datasheet, with R1 equals R2:

\( -1.25 \left (2 \right ) + (120\,\Omega \times 100\,\mu\text{A}) \approx -2.5\,\text{V}\)

I will try with 1 % resistors, I will buy these during the week. : )

 

There are dozens of 2.5 volt regulators. If you would say what you need instead of what you want (an exact complement to an LM2937), you might some good results.

Do you need -2.5 volts at 500 ma?
Do you need 1/2% accuracy?
Do you need it in a 3 pin package?
Do you need it to survive 60 volt surges?
What is the supply voltage?
What is the actual current you need?

 

I need a -2.5 V regulator with -5 V input from a 7905.

The load current is not a problem, it will be very low, no more than 10 or 20 mA because I need it for reference voltage and for an op amp supply with high load to its output. TO220 package for the regulator is good enough.

Thank you in advance.

 

The LT3015-2.5 has a -2.5V fixed output.

 

Thank you crutschow !

 

Finally I found at home 2 resistor of 100 Ohm 1 % tolerance. I tested the LM337 with them instead of using the trimmer and it works like a charm.

Thank you all guys.

 

1% resistors will give a worst-case voltage error of ±1% plus the ±2 tolerance of the LM337 internal reference (at 25°C) or ±3% total output voltage error from nominal.