How would you make a linear regulator's output voltage dependant on its input voltage

[si2030]

Hi guys, Mr Al,

Yep seen the circuit and I now understand that the pre-regulator should be the slave... following the linear regulator's voltage setting. My intention was to build a switching pre-regulator and at the same time wind my own transformers. The idea (bigger picture) was to try and gain an understanding of the TL494 chip PWM techniques and have a stab at creating a more efficient higher power bench power supply than the 3 amp offerings on eBay... thought it would be a good idea to learn something along the way!

The intention was to have two LT1083s in series each with a 0.015 ohm resistor in series (as per datasheet). It should be adjustable between 0 and 30 volts and there should be a switching pre-reg up wind using PWM. It should manage 10Amps max - have adjustable current limiting.

Yes well with regard to the last comment - I actually do have a schematic of sorts - I am following the datasheets for the TL494 and TL1083 as well as the application report "Designing Switching Voltage Regulators With the TL494" by Patrtick Griffith. There are quite a large number of functions associated with both the TL494 and LT1083 and until you have a good understanding about how they work its difficult to just draw up a schematic in full. Logic suggests you explore you options and limitations of each IC and how they might be used together. Using the bread board to check that these concepts work the way you want them to and then finalising the schematic... Issues relating to how to use a prereg in this instance, how to design a switching transformer properly, how to wire up the TL494 for a specific driver topology and how to add in a linear regulator correctly. These are things that you cannot just enter into google and up they pop... I've tried.

I do appreciate the constructive comments and apologise if the questions appear inane.

 

[alec_t]

You're going the right way about it...mugging up on the datasheets and getting to know the ICs little foibles before actually building something. Too many hopefuls build things first then wonder why they don't work. In various other posts to this forum you will see 'read the datasheet' advice being given .

 

[Sceadwian]

You're going the right way about it...mugging up on the datasheets and getting to know the ICs little foibles before actually building something. Too many hopefuls build things first then wonder why they don't work. In various other posts to this forum you will see 'read the datasheet' advice being given .

I couldn't agree more!

more efficient higher power bench power supply than the 3 amp offerings on eBay

I'm not trying to dissuade you in fact I applaud your efforts and hope much comes of it, but there is a reason those basic units exist. Sure they're not efficient but very simply put they work! work well, and work without a lot of investment. There is a bit of a gap between cheap linear supplies and more expensive higher power units that use SMPS/linear hybrids but it's difficult to justify the design time to do this efficiently, sure they waste a lot of power but their regulation is fantastic.

Your case is however unique as you will definitely learn a lot on the journey and very possibly in the end have something to add to the community if you manage to trudge through all the design hurdles that will pop up.

I certainly couldn't do it! Best of luck!