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Topic: difference between an amplifier and a voltage regulator  (Read 377 times) previous topic - next topic

rosemerry

so i am using an Amplifier , and it works well , i am using a dual power source for it in the form of two 9v batteries (+9v and -9v) .
instead of two batteries , i would like to use a 12v power source instead ; so i need it to be +6v and -6v .
so what occured to me is to just use 6v as reference and just hook ground to the negative rail and 12v to the positive rail .

now in order to obtain the 6v low impedance output there are two things that i thought of :

   -- using an Op-Amp (TL072) as a buffer and just using a voltage divider (1/2) on the 12v line and then hooking it up to the op-amp .

   -- using a 6v voltage regulator (L7806)

what's the difference between the two solutions ?
i am an old man

jremington

Please post a link to the "Amplifier" and describe what it is supposed to do. There may be a better solution.

rosemerry

Hello ,

here is the circuit design , it's a circuit meant to read muscle signals .
i just replaced the ina106 with an AD620 ; everything else is the same .
for now it uses two 9v batteries ; and it works .

i am an old man

jremington

That circuit is intended to amplify extremely weak signals obtained by direct contacts with human skin, and to be battery powered for personal safety and electrical isolation.

Unfortunately, any attempt to power it using an external power supply, especially from a household AC source, could be lethally dangerous. It is also very likely to fail due to electrical interference from house wiring, overhead lights, ground loops, internal power supply hum and noise, etc.

Just use batteries as intended.


rosemerry

i am an old man

MarkT

so i am using an Amplifier , and it works well , i am using a dual power source for it in the form of two 9v batteries (+9v and -9v) .
instead of two batteries , i would like to use a 12v power source instead ; so i need it to be +6v and -6v .
so what occured to me is to just use 6v as reference and just hook ground to the negative rail and 12v to the positive rail .

now in order to obtain the 6v low impedance output there are two things that i thought of :

   -- using an Op-Amp (TL072) as a buffer and just using a voltage divider (1/2) on the 12v line and then hooking it up to the op-amp .

   -- using a 6v voltage regulator (L7806)

what's the difference between the two solutions ?
Only the amp will work.

Voltage regulators can only source current(*), not sink it, whereas the virtual ground you are imagining must be
able to source and sink (that's what dual rail amplifiers assume).

In effect you'd use one amp to define ground for the other.  The first amp must be single ended and dc coupled.

Typically if you have a single supply, use a single-supply amplifier.  Its much less hassle.


(*) well positive voltage regulators can't sink current, but then negative voltage regulators can't source it.
[ I will NOT respond to personal messages, I WILL delete them, use the forum please ]

gilshultz

Your suggestion "  -- using an Op-Amp (TL072) as a buffer and just using a voltage divider (1/2) on the 12v line and then hooking it up to the op-amp ." could work, just add two transistors and a decoupling cap.  You need two transistors.  Connect the collector of the NPN to the + and the collector of the PNP to ground(12V-). Connect the bases together and connect to the output of your opamp.  Then connect the Emitters together as your output. The op amp would be configured with the + at the junction of the two resistors (6v). The minus to the Emitters preferably through a 10K resistor.  You will have to decouple it with a cap or two.  Remember the Ground is not the same as any terminal on your power supply.  Connecting this to anything else needs care. You did not state what you were doing with the outputs however this will give you what you need.

Good Luck, and Have Fun! Gil
This response is to help you get started in solving your problem, not solve it for you.
Good Luck & Have Fun!
Gil

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