getting -5V from 5V supply to drive opamp?

[ahgu]

I need to get true zero from the opamp. So I need -5, or maybe even -1 for that purpose. It is best to get -5v to match the +5. Power has to be linear regulated . Is there a simple idea out there? can I just stack 2 LDO together and use the middle as ground?

thanks
Ahgu

 

[IanP]

There is no way of generating -5V of +5V in linear configuration (regulation).
Instead try DC-DC/Charge-pump converters which generate -Vout of +Vin.

Examples:
ICL7660
MAX660
TC660....

can I just stack 2 LDO together and use the middle as ground?

If you have 10V you can use attached circuit. 5V is not enough..[/img]

 

[radigital]

If you wish to generate negative voltages, the good strategy is to use
some sort of a charge pump configuration which charges a capacitor
to 5V, and reverses the capacitor terminals. I am not sure whether
you can generate a perfect -5V from 5V, but surely you will get a
negative voltage enough to produce 0V for your opamp.

 

[ahgu]

Why cannot I use 2 LDO?

like 2 batteries, stacked on top on each other, use the middle as ground.


+ - GND + -

 

[IanP]

You can use 2 LDOs or circuit from my previous post with the same effect. In both occasions to have +/-5V output you will need in 2-LDO case about ≥11V and with (1 or 2) opamp 10V supply..

Other option is to use 1 silicone diode (1N4148, ...) with 1kΩ resistor from 5V and create voltage devider (+4.3) - 0 - (-0.7). This should be enough to drive opamps such as CA3130 and have "true" 0V output.

 

[ahgu]

I don't understand if the R and diode circuit will work.

you have 5V ----R--------gnd-----------Diode-----------(-0.7)??


I don't think the OPAMP supply will force it to be -0.7v.


If it work, Single Supply opamp designer can just do that and I don't have this problem.

-ahgu

Added after 8 minutes:

I understand what you mean now. if the load change, the negative -0.7v changes also, maybe too much noise.

 

[IanP]

Attached is the circuit.

 

[VVV]

You can build a crude charge pump with an old 555 timer. It should give you some -3.5V, which should be enough for your purpose.

Depending on your application you may be able to just split the input power with another opamp and a couple of transistors, or even insert a couple of diodes in series with the circuit's return and power the opamp V- from ahead of those diodes.

 

[cetc1525]

you can use a dc-dc to stable the negative power supply.