ground from 24Vbattery to dual voltage regulator

[mhdanas]

Hi
i'm new here just i have problem with my circuit i need dual voltage positive and negative from battery i used (LM317&LM337) but the problem from where i can take ground and i need like 500ma current i don't know about use Resistances to make middel point good idea maybe zener but i don't know if any one have better idea
thank u

 

[crutschow]

How much ground current is there (the difference between the positive voltage and negative voltage currents)?

 

[mhdanas]

mm i wrot i need near 500ma ground i use pic and 12 relay DAC and amplifier and few stuff on positive side and i need negative voltage as referans for ampli and for DAC (i use dac0808 and ampli lf351)
thank u for ur help

 

[MikeMl]

The only way to do this without using a switching inverter is to use the center tap between the 12V batteries as a "floating" ground reference for the split power supplies, so you can generate a negative voltage referenced to the tap. Note that this is not a good solution because the load seen by the two batteries connected in series is imbalanced, resulting in one battery being more discharged than the other. The only way of restoring the state-of-charge balance between the two batteries is by chronically overcharging one battery to keep the other fully charged.

 

[mhdanas]

thank u Mike but it's not good idea as u said too i'm asking about way to make it like two resistor between the 24 poles and take from middle ground but i don't know if it acceptable for 500ma or i don't know maybe zener just i'm asking if some body try it or have better chose
and thank u

 

[crutschow]

You could use an active circuit to generate the virtual ground at 12V but it would be wasting 6W of power, which the virtual ground circuit would have to dissipate . Here is an article on virtual grounds.

You would need a high power buffered design. Attached is a circuit using an op amp and a MJ2501 PNP darlington power transistor or similar, which must be on a good sized heat sink. You only need one transistor since your circuit is unbalanced with an excess of plus current that needs to be routed to the negative side.
(Note: Do not connect the 24 ohm resistor. That is just to simulate the 500mA load you have.)

 

[mhdanas]

really thank u so much the article so helpful and the circuit nice too i think i'll do it just what do u think about this thought **broken link removed**

 

[Hero999]

I thought the supply voltage was 24V?

The problem with zeners, is the output current is low, unless you use large diodes and a power resistor which consume lots of current.

Here's another virtual earth circuit.

 

[crutschow]

I thought the supply voltage was 24V?

The problem with zeners, is the output current is low, unless you use large diodes and a power resistor which consume lots of current.

Here's another virtual earth circuit.

Due to the added high gain of the two common emitter output stages in cascade, without compensation that circuit may exhibit instability or oscillations.

 

[Hero999]

What do you mean? The output stage is a follower.

The booster transistors have no voltage gain so no, that won't happen.

I decided to opt for a Sziklai pair, rather than a Darlington because there's less dead band so the op-amp's output won't have to jump so much.

I did forget to put a decoupling capacitors from the virtual ground to either supply rails though.

 

[crutschow]

The booster transistors have no voltage gain so no, that won't happen.

I decided to opt for a Sziklai pair, rather than a Darlington because there's less dead band so the op-amp's output won't have to jump so much.

Your are right of course. I just looked at it wrong.

 

[Hero999]

That's understandable, it does look confusing at first glance.

Another thought :the good thing about using transistors like this, is it's really easy to do current limiting, if required - just add a couple of sense resistors and another pair of transistors, I'll post a schematic if the OP wants me to but it's probably obvious to you.

 

[mhdanas]

thank u so much guys u really helped me, yes plz post schematic i don't need it here but to add it to my knowledge, if it not use much time from u,
thank u again

 

[mhdanas]

thank u so much guys u helped me
best wishes

 

[buckysparks]

This document shows how to generate a positive/negative output voltage from a dc voltage source.
It uses a single ic and a coupled inductor to create both outputs.

https://focus.ti.com/general/docs/litabsmultiplefilelist.tsp?literatureNumber=slva369