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I have a circuit that has an input of 24VDC. The circuit has two different voltage rails requirements. 12VDC @ 0.1A and 8VDC @ 1A. I have decided to use a swithching regulator from 24VDC to 8VDC, and a linear regulator from 24VDC to 12VDC. My concern is that there will be a power dissipation of 1.2W on the linear regulator and I am not sure if this is right direction I should be going in.

My Possible solution to this was to use a switching regulator from 24VDC to 12VDC (Iout = 1.1A), and another switching regulator from 12VDC to 8VDC(Iout = 1A). But I am concerned about the possible interference/noise this may cause if I two of the same Switching regulators (Same switching frequency).

It makes no sense to me to use a switching regulator on the first set up for 24VDC to 12VDC @0.1A as the current demand is less.(0.1A is a fairly liberal estimate as the circuit does run on 25mA, and I plan to add a LED which might draw another ~10-20mA).

This Is the Circuit I have currently designed. enter image description here

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If the linear dissipation is a concern, then another switcher is what you need.

Having said that, I used to produce a lot of designs using discrete switching controllers, but unless space is really a premium, or you are doing volume manufacture (where cost is critical), there is a huge amount to recommend off the shelf solutions.

In this case, you might find it helpful to know that there are a number of suppliers who effectively provide drop-in replacements for linear 3-pin regulators but which internally use switching.

So for instance, this unit here would more than cover the 24V-12V requirement, and is less than $3. You can also get SMT adjustable versions, for only a little more, that would cover your 8V 1A requirement.

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