1.2-30V 1A split power supply design

[carbon dude oxide]

I am thinking of putting a linear regulator on the end and using the smps to drop the voltages down so that the linear regulators are not bathing in magma

[madires]

I am thinking of putting a linear regulator on the end and using the smps to drop the voltages down so that the linear regulators are not bathing in magma

Then you have to synchronize the buck converters and linear regulators and keep the voltage drop of the latter in mind.

[carbon dude oxide]

Yes i did have that though of making sure that the voltage comming out of the smps is at least 2v higher then the linear regulators

This is why i thought it might be better with a micro controler so that i can program it all but a potentiometer solution will probably be easyer to use

[carbon dude oxide]

Ok so if we ignore the transformer for now would this be a working setup?

[c4757p]

No.

1) MC34063 has a maximum peak switch current of 1.5A. For a buck converter, that gives you only 750mA output, even less for inverting.
2) MC34063's maximum voltage is 40V. In your inverting configuration, you have +35V on Vcc and V- on gnd. That means it has 35+|V-| applied across it, with is sure to be more than 40V.

Yes i did have that though of making sure that the voltage comming out of the smps is at least 2v higher then the linear regulators

This is why i thought it might be better with a micro controler so that i can program it all but a potentiometer solution will probably be easyer to use

That offset can be done easily with an op amp.

[carbon dude oxide]

I dont know why i put that part number on there :/ but in theory if there is a ic that can do that would it work?

[c4757p]

I dont know why i put that part number on there :/

Or that part itself! You've used it correctly, except for the voltage and current limits. 

But yes, it looks fine to me.

[carbon dude oxide]

What controlers allow for inverting from +35 volts down to -30 ?

[Paul Price]

Nunofdem.

You build two isolated supplies, each identical with each having a separate power transformer to make two power supplies and one is your positive and the other your negative 3A supply.

Please see what I've said in an earlier reply.

The negative supply is no more than the same positive power supply circuit standing on it's head.

[carbon dude oxide]

Ok would it be possible to do the centre tap idea but have multiple linear voltage regulator stages seperated by 7-8V and switch between the outputs of them? That way i can have the positive and begative rail and not go over 8v between input and output. It may only be 1.5A but i do have a beasty heatsink at home just sitting there which i could use.

[Paul Price]

Draw a schematic.  Sounds like it might work. Details please.

[carbon dude oxide]

ive had alot of thought on my last idea but i have decided it will not work very well :/  one of the main reasons is when i initially thought of it i was thinking of some nice ideal lm317/lm337 regulators with no internal voltage drop T.T

i have however come up with another idea in the prossess which expands on another idea someone else has posted about having a multi tap transformer. unfortunately i cannot find many multi taps so im maby thinking of and idea of having multiple transformers along with a microcontroler controlled input so when it comes to switching from one transformer to another it can match the output voltage just before switching rails.

i will draw a schematic out of how i think it might work

[carbon dude oxide]

Ive done a bit more research and have come accross this which uses an LM723 as the regulator bit it only does te positive side voltage regulation

http://elect.wikispaces.com/file/view/N0006D05082009.pdf/97924473/N0006D05082009.pdf

[madires]

Ive done a bit more research and have come accross this which uses an LM723 as the regulator bit it only does te positive side voltage regulation

http://elect.wikispaces.com/file/view/N0006D05082009.pdf/97924473/N0006D05082009.pdf

Please read the datasheet of the LM723, it supports negative voltage regulation too. BTW, I'd use a BD135/137/139 for Q1.