High current voltage regulator using lm7824

[tigox]

Hey there, so in the future i'm building portable speakers with a tda7294 anplifier off ebay, the problem is i'm running this from a battery so i'll need an smps power supply to give me double supply off my battery, so the smps gives out +-35v but the amplifier only takes in 24-0-24 at max, so i was thinking of making a high current voltage regulator.
I've been seeing a lot of circuits like this:

the problem is that i also have a negative regulation going on, and it might get unbalenced....
so what i am thinking of doing is instead of the zener i would put an LM7824 to control the base of the base pin of the transistors

So i first, will this work??
and second could i use the lm7824 for both the negative and positive transistor's base , or will i need an LM7924 for the negative transistor's base?

Thank you for your time D

 

[vacuphile]

It might be more economical to find an smps that delivers the right voltage. First of all because it will not cheap to build this regulator, if only for the heat sinking you will need. Second, you will waste precious battery power with this scheme, at least half of all your battery capacity, and.probably more.

 

[tigox]

It might be more economical to find an smps that delivers the right voltage. First of all because it will not cheap to build this regulator, if only for the heat sinking you will need. Second, you will waste precious battery power with this scheme, at least half of all your battery capacity, and.probably more.

yeah i though so.... so any other ideas? :S because i for the life of me cant't find an smps with +-24v

 

[vacuphile]

Tigox, they must be out there, otherwise you might consider cascading two 24V units.

 

[tigox]

Tigox, they must be out there, otherwise you might consider cascading two 24V units.

i'm sorry but what do you mean by that? :S

 

[MarianB]

@tigox it is a complete waste to have a SMPS with usually good eff rising the voltage and then have a linear regulator to stabilise the voltage at a needed level, linear regulators wase lots of power on the series pass element, i would never use this combination.

Any SMPS can be modified for lower voltage cus that usually means lower power so a smaller stress on the power elements, if the SMPS is regulated then just by changing the upper resistor on the voltage divider of the feedback network will reduce the voltage at the needed level, if the SMPS is not regulated then you need to modify the power transformer, rewind the secondary coils for the needed voltage.

If you are not sure what to do then post the SMPS schematic here and i will try to guide you trugh it.

 

[Elvee]

Have a look at this: http://www.diyaudio.com/forums/powe...anion-circlophone-move.html?highlight=boostor
It is not comparable to present-day, state of the art converters for efficiency, but it's still OK, and much better anyway than what you intended to do.
It is also cheap, low-tech and reliable

 

[vacuphile]

i'm sorry but what do you mean by that? :S

If the SMPS has a floating output, that is, if there is no connection to ground on either of the outputs, you can use them just like batteries. Connect minus of one SMPS to the plus of the other, and this point will be your ground. You will then have +24 and -24 around that ground.

 

[MarianB]

Why wasting money one another 2 units when he already has 1 functional one? lowering the voltage is much easy than raise it up even if it means rewinding the transformer.

 

[vacuphile]

Sure MarianB, if you know how to do it (safely).

 

[MarianB]

If i didn't, then i wouldn't have mentioned it.