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# Problems with power supply

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#### rina_1220

##### Member level 2
Hey there. I'm working on my graduation project and all my project should work with only a 3V lithium battery as a supply and it has to be as small as possible.
I need to use some operational amplifiers and for tests and prototyping I'm using the TL071 ones, which are working fine. The only problem is that they require dual supply (+-3V).
What choice would be best to help me? Find some low noise, single supply op amps or to use a negative voltage regulator to get +-3v for the opamp?

I've been doing some tests with OPA335 as well, but their output voltage goes only from 0 to 5V and I end up losing the negative part of my signal.

Maybe you could try DC-DC converter with the ratio of -1 (negative buck DC-DC converter with 1:1 converter ratio will be ok)

I'd use single supply OA, and AC couple the input signal, setting signal reference to 1/2 of power supply.

u can easily use 2 lithium batteries.

for +3 use one battery and for -3v, use other battery in reverse.

(I think using this logic u can accomplish this using single battery, let me know when u succeed)

Naveed

I thought of using 2 batteries. But the problem Id face is size. It cannot become so big, nor heavy. So I think 2 batteries would be too much.

Hi Rina,

Iam not quite sure tis gonna work..may be just an idea...!!

I thought that you could draw just the opposite polarity from the same battery, with proper grounding and rest assured you may succeed. The only issue that would be, whether the battery with this connection can still drive your circuitry..!!

Please check... and tell me .!!

Sai

rina_1220 said:
I thought of using 2 batteries. But the problem Id face is size. It cannot become so big, nor heavy. So I think 2 batteries would be too much.
Then use one battery.
for +3v, use normal connection.(+Vcc)
for -3v, reverse the battery connection.(-Vee)
am I clear??

Naveed

Naveed Alam said:
Then use one battery.
for +3v, use normal connection.(+Vcc)
for -3v, reverse the battery connection.(-Vee)
am I clear??

Naveed

Sorry.. didn't get ya

ok..
suppose pin no. 2 and 3 are for Vcc(+3volt)
and pin no. 4 and 5 are for -Vee (-3volt)

Then take a battery and connect, its positive terminal with pin no. 2 and negative with pin 3. (+Vcc connections are done)

now, for -Vee connection, connect same battery's positive terminal with pin 5(instead of pin4) and negative terminal with pin 4(instead of pin5), these reverse connection will result as -Vee connections.

I think u will understand my point now.
Or call on my cell, for more clearance..!!!
got my point??

Naveed

why don't you use a digital logic inverter?

Hi rina...

I was using multisim (v9) and tring to simulate some small ckts (analog) with the kind of connections me and our friend naveed...

for +3v, use normal connection.(+Vcc)
for -3v, reverse the battery connection.(-Vee)

had suggested. They seem to work OK.....

Just thought your case should work tooo....

All the best..!!
Sai

you can use of tl07(or oter op amp) and use of virtual gnd.connect +3 to +vcc of op and gnd to -vcc of op.make an voltage divider with two 10k resistor .so 1.5 volt droping in each res.you can use of this voltage for virtual gnd.this means connect gnd of circuit to this voltsge.and for better response use of 1uf capacitor in parallel with second resistor.

In case the previous ideas do not fulfill your needs, you can try a charge pump ckt.

Intersil and Maxim have such devices that allow to get a negative voltage from a positive one. You also can do it with inverters and capacitor.

Do not remember if the IC I mentioned work from 3 Volts as I´ve use them with +5V

Regards

you can use LMV324 it is single supply 3v low current amplifier with the same characters as tl074.

bwood1234 said:
why don't you use a digital logic inverter?
This is a good idea.

Or you can use a 6V battery. I think they should be at same size.

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