### Author Topic: how to supply negative voltage for opamps  (Read 2898 times)

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#### BEAMer

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##### how to supply negative voltage for opamps
« on: May 31, 2008, 08:23:37 AM »
hi,

iam a undergrad student from india and i build BEAM robots. i have a big problem which may sound a little silly. how does one produce negative voltage for opamps....? i have constructed a circuit with two voltage regulators (7818 and 7918) producing + and - 18 volts respectively. but this circuit has two grounds also. it does not have a common ground... what do i do now? if i try a common ground the voltages are different. what do i do? please help me...!

BEAMer

#### Steve Joblin

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##### Re: how to supply negative voltage for opamps
« Reply #1 on: May 31, 2008, 08:50:23 AM »
You don't want a voltage regulator... you want a voltage inverter... google "ICL7662" to find the spec sheet... the idea is to first use a voltage regulator to get the proper + voltage, then send that regulagted + voltage through an  inverter to get a regulated - voltage.

#### benji

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##### Re: how to supply negative voltage for opamps
« Reply #2 on: May 31, 2008, 09:03:16 AM »
mm this is just a matter of relativity
if you want 0 and -5  then just make the + of the battery as your circuit common and use the - as the -5 (so no need for any ICs)

if you want -5 ,0 and +5 then you can use a transformer that gives 3 terminals ,,the middle is 0 (common)

if you want to regulate these voltages then yea you need 2 regulators
first reg input is +5 and the common is the 0
second reg input is 0 (circuit common) and the -5 its common

so now you have 3 terminals to use into the circuit

1/ first reg out wich is +5
2/second reg out which is 0
3/ -5 (directly)

this way you did regulate both voltage   (5>>0) && (0>>-5)
good ol' BeNNy

#### benji

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##### Re: how to supply negative voltage for opamps
« Reply #3 on: May 31, 2008, 09:05:57 AM »
Quote
i have constructed a circuit with two voltage regulators (7818 and 7918) producing + and - 18 volts respectively. but this circuit has two grounds also.

this means your wiring is wrong , post a schematic n  we'll fix it up for ya
good ol' BeNNy

#### Admin

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##### Re: how to supply negative voltage for opamps
« Reply #4 on: June 07, 2008, 04:35:54 PM »
Ummmm just connect the grounds together (to make them common)

#### awally88

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##### Re: how to supply negative voltage for opamps
« Reply #5 on: June 08, 2008, 09:43:23 AM »
Quote
if i try a common ground the voltages are different.

really?

#### BEAMer

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##### Re: how to supply negative voltage for opamps
« Reply #6 on: June 09, 2008, 06:09:22 AM »
as Mr steve suggested, i have bought a voltage inverter and its very cheap.. i have used it and i got the necessary results.. Thanks Mr steve, Benji, Admin and awally88 for your valuable suggestions...

BEAMer

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