I need to generate from 0 to -8v. If I used a negative voltage supply to a
LM324 (that's the OpAmp I have).Will I get negative voltage?

Or is this the same as setting the OpAmp for a dual voltage (+/-) and making it an inverting amp. Will I get negative voltages?. The device to connect will be a dynamic microphone, louder sounds must generate more negative values.

Thanks,

 

No, to generate negative voltage, you need a negative power supply.

Do you need a positive voltage as well?

If not, then just call the +V, 0V.

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The LM324 is designed to work with either a pos. single supply or dual +/- supplies.

 

No I don't need positive voltage.

You wrote "...to generate negative voltage you need a negative power supply". That was my original statement "I need to generate from 0 to -8v. If I used a negative voltage supply to a
LM324 (that's the OpAmp I have).Will I get negative voltage?" So I am correct in my assumption.

On the other hand how do I "just call the +V, 0V." are we describing the same thing?

Thanks,

 

I believe Hero999 was telling you to reverse the supply pins and connect the pos side of the supply to the grd pin and the neg. to Vcc. This won't work however, because as I stated before, you can use either a single pos. supply or dual pos and neg. supplies.

 

OK. I see. Then using a dual supply -> +/- ,how do I get only negative output voltage? Again I will be connecting a dynamic microphone to the LM324, as the sound capture from the dynamic mic gets louder I need a more negative voltage.

Thanks,

 

Here's a negative supply and no positive supply.

Attached Images

neg supply.GIF (1.5 KB, 13 views)

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Can you provide a schematic?

 

You may float the non-inv pin of op am at 1/2Vcc and manage the show without need for neg. voltage
suppose you have 2 resistor in series from Vcc to gnd. the mid point can be set at a nominal half point
this can be referred to + in the the output would be swinging either side of half Vcc.
Generally the negative voltage doesn't demand much current. If you still want to have -ve voltage you may consider using classic MC34063which can generate -ve voltage.
Of late there are modern chips of very small footprint and can also be used .

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Sarma.

 

Thanks for the response. Can I used an LM324 with a mid point resistor divider voltage supply but setting the positive connection of the LM342 on the mid point of the voltage divider and IC negative to the negative of the voltage divider, will it generate negative voltages?

 

It won't generate negative voltage at the output.

output will switch between 0 and near Vcc for input(on Non-inv input) being less / more than the Vref,
in comparator mode.

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Sarma.

 

....The input will be dynamic microphone..if I used the LM324 as amplifier with a dual (+/-) voltage -> the signal will fluctuate positive and negative relative to 0 volts -> (is this a correct interpretation?) if I rectify the output for only the negative part would that be negative voltages?

 

The lousy old LM324 is too noisy (hisssss) to be used as a microphone preamp.
Its audio high frequency response is poor and it has crossover distortion.
The LM324 has 4 opamps inside. The LM358 is the same but has 2 opamps inside and is in an 8 pins package.

If you use a positive and negative supply then when you recify the output it can be positive or negative.

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I will not be using the actual sound but the sound pressure. I Hope the noise is not a issue. Anyway I wil do some testing and see what happens.

Thanks to all.

 

AudioGURU has rightly pointed to the HISS aspect of LM324
the audio pressure should only concern to what you fed. But it will add additional pressure as pointed by AG. it is better to avoid it if possible

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Sarma.