DC Power Regulators vs. DC-DC Converters

The best solution is to draw from the 24V supply as long as you don't draw more current than the supply can provide.

All else being equal adding the regulators will involve less parts and headaches.

You will still need to add noise filtering for your sensors as good design practice dictates.

The problem with regulators is the power they will dissipate.

eg. 5v at 1 amp from a 24v supply.....you are wasting 19v at 1 amp (roughly)...that's 19W !!!

There are plenty of DC-Dc converters about or chipsets if you want to build your own. A compromise would be say a DC-Dc converter down to 5v and then a regulator down to 3.3 from the 5 so it wouldn't dissipate so much.

>>The problem with regulators is the power they will dissipate.

eg. 5v at 1 amp from a 24v supply.....you are wasting 19v at 1 amp (roughly)...that's 19W !!! <<

Good Point Del

The linear regulator approach is quick and simple to design and build but energy wasteful.

There are a good number of DC-DC converters available so getting your 5V and 3.3V is doable without the use of the less efficient linear systems at the cost of a bit more design effort.

Cheapest / laziest solution?
Find an off the shelf laptop supply that provides the voltages at the power levels you need, but thats no fun.

Most computer power supplies will have those voltages...

if you use 7805 for 5V from 24v, it will be more power dissipaton.

in fact you can find more chips for dc-dc that from 3V to 60V on the market.

1. In linear Regulators design you have to keep the off-set of approx 2-3V in the I/P of regulator to keep the dissipation across the regulator minimum. It is not necessary for efficincy but also for the protection of the device [to keep cool].

2. This is achieved in DC-DC-Converters by SM operation.
For a single supply linear-reg is economical, use a step-down transformer with an O/P + 3-4V to required DC O/P.

3. In Multi-supply voltages you may have muli-output transformer having the voltages O/Ps + 3-4V to required DC O/Ps.

3. In SMPSs mostly [like PC-PSU] each supply is not regulated individually by linear-reg-device or dicrete-Cct but only most critical supply is done and all the rest are considered to be regulated within limits.

4. In variable-voltage supply [non-professional] for general purpose you may get multi-step-supply ranging from 3V to 12V in steps 5 or 6, 7.5, 9 and 12V.

5. I had come across a professional Hi-Power linearly-Variable supply by HP.
It used a Pre-Regulator concept met by a Semi-Variac

[had half tthe windings on lower-layer & upper layer on which slider moves had rest of the windings].

6. This all is done with linear tech.

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MOREIRC
I have a 24V supply (switching). I need to get add 5V and 3.3V.
I also, obviosly have 120V 60Hz available.
What would be the best way to get 5V and 3.3V.

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My suggestions are:

a. There a lot of DC-DC Converters 12V, 24v by various manufacturers. look for a data-book in the market & search.

OR


b.In Multi-supply voltages you may have muli-output transformer having the voltages O/Ps + 3-4V to required DC O/Ps and use the linear-regs like 780x as you need.

c. In variable-voltage supply [non-professional] for general purpose you may get multi-step-supply ranging from 3V to 12V in steps 3, 4.5, 6, 7.5, 9 and 12V.

Thanks all for the input. Looks like I am going with DC to DC.