Hi there,

I need a -5V to power up the INA126 chip used in my project. I know i can use a voltage regulator to do that. what i will like to know if there are any other options. my concerns are, cost, current consumption(as little as possible), bulk(how big the circuit is going to be).

From what i understand, voltage regulator do chew up a substanitial amount of current from the battery. i aim to reduce that effect. so i was hoping someone out there can help me with this.

thanks

alvin

 

LM7905, cheap, 3 pin to-220 regulator @ 1A
alternative is a 5 volt Zener diode with a resistor ( Ohms dependent on VCC)

 

What supply to the circuit have you got? You could use something like an ICL7660 to convert +5V to -5V which would have lower power consumption compared to a 7905 but would take up more space.

Up to you to decide

 

with a 79xx you still need a negative supply to begin with... Don't you?

 

A -5V regulator doesn't MAKE negative voltage, it only regulates it.

ICL7660, MAX1044 will turn 5V to -5V. It's limited to a few milliamps and is not regulated.

What are you trying to do with the INA126? If you have a digital system, you can drop the amp and go with an unbuffered ADC which can accurately read signals -0.3 v below ground without using a negative supply.

 

If the circuit you have isn’t on batteries you can pickup some current with a capacitor at the rectifier. This can be filtered and regulated if necessary but only for low current output.

Ante :roll:

 

it'll take up more space but couldn't you use a hex inverter or a smaller type if you can find it?

 

Um, hex inverter as in a logical inverter? That's got nothing to do with creating a negative voltage.

 

yeah the inverter will just turn 5V to 0V and 0V to 5V. it cant make negative voltages

 

hi there,

i've took note of all the replies. thanks.

The INA126 will be used to detect heartbeat signal. as this signal is pretty small and susceptible to noise, i felt that i would need a chip thats designed for it. i tried and tested the chip and it works. so i dun have much of a choice. i tried using LM324 to build the exact same circuit but it doesnt work as well. apparently the signal picks up a lot of noise which makes it impossible to read it off the scope.

"with a 79xx you still need a negative supply to begin with... Don't you?"

is this true???


"alternative is a 5 volt Zener diode with a resistor ( Ohms dependent on VCC)"

How do i do this? i know how to obtain +5V but not -5V using a zener diode


"A -5V regulator doesn't MAKE negative voltage, it only regulates it."

What does this mean??

hope you guys can help me answer these questions.
Thanks alot

 

A regulator takes a voltage (maybe approx 12v) and 'regulates' down to another voltage (a 5v reg gives out a regulated 5v output...). In the same way that a +5v reg needs (for example) a +12v input, a -5v reg would need a -12v input.

Any help?

 

both of the above statements are true. if u see the datasheet for the 7905 regulator on national semiconductor's website u will see that these regulators need a negative supply in the first place. u see these regulators are negative voltage regulators and not negative voltage generators. they only "regulate" a negative voltage. this negative voltage can be from anything, a bridge rectifier for instance.

if u see the datasheet, in the Absolute maximum ratings section its written that the maximum input voltage is -25V for the 7905 and the maximum input-output differential for the 7905 is 25V. and -10V is a typical input voltage for the 7905.

nowhere does it say that a 5V will be turned into -5V. for that u need a DC-DC converter. a DC-DC converter is different from a voltage regulator. its a different domain of power electronics. and 5V to -5V converters have already been suggested to u in this post above.

i hope that helps

 

Why not? If one inverter formed an oscillator, another five work as buffer, via seriel capacitor and a voltage doubler possible You can make a negative voltage...

 

well if u put it that way, then yes it may be able to provide a negative voltage. actually the person who said that a hex inverter will be able to provide a negative voltage didnt tell how it would do that. have u ever produced a negative voltage by doing this? do u have a schematic

 

Hey,

thanks alot for all your replies. i might just go for the chip to get the -5V. if anyone out there have any new ideas, pls post it. i will be watching this newsgroup as often as i can. i was hoping of using components tats cheap and will take up minimal space on the PCB.

Thanks alot.........