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Electronics => Electronics => Topic started by: BEAMer on May 31, 2008, 08:23:37 AM

Title: how to supply negative voltage for opamps
Post by: BEAMer 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

Title: Re: how to supply negative voltage for opamps
Post by: Steve Joblin 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.

Title: Re: how to supply negative voltage for opamps
Post by: benji 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)

Title: Re: how to supply negative voltage for opamps
Post by: benji 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

Title: Re: how to supply negative voltage for opamps
Post by: Admin on June 07, 2008, 04:35:54 PM

Ummmm just connect the grounds together (to make them common)

Title: Re: how to supply negative voltage for opamps
Post by: awally88 on June 08, 2008, 09:43:23 AM

Quote

if i try a common ground the voltages are different.

really?

Title: Re: how to supply negative voltage for opamps
Post by: BEAMer 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