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Its a good practice use dc-dc converters and linear regulators? Or its better don't mix them?

Better use all linear tecnology or dc-dc converters in "cascade" or dc-dc with multiple outputs?

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The answer to that depends heavily on your application. What are you trying to achieve? Efficiency? Low cost? There is nothing wrong with using both in a design. – Jason May 16 '13 at 0:35
In some cases using a switch-mode converter followed by linear can improve efficiency and result in less noise. – AndrejaKo May 16 '13 at 0:38
As a rule of thumb, you'd want the switcher if the dropout voltage is large. E.g. to go from 15V to 3.3V, switcher. But if we have a switcher that goes from 15V to 5V, then 5V to 3.3V could be a linear LDO and not another switcher. – Kaz May 16 '13 at 0:56
up vote 8 down vote accepted

The short answer: Yes, it is fairly common to mix different types of regulators in the same design.

The long answer: It totally depends on what you are trying to do. Switching regulators are going to be more efficient, but linear regulators are going to be less noisy. If you are working with noise critical applications like audio or video processing, you might have to use linear regulators just to keep the signal from being so noisy.

Cascading regulators can help - using a switching regulator to drop most of the voltage, then a linear to create the desired level - but even this might produce too much oscillation on the power line from the switching frequency. This can often be controlled with a ferrite bead or other passive filter, but sometimes, straight linear is the only way to go.

On top of that, switching regulators are typically more expensive and use more components than linear ones, so when efficiency isn't an issue the component cost factor may be the deciding factor. However, as noted by AndrejaKo, efficiency does have a big impact on operational cost, and additional cooling consideration may need to be taken when using linear regulation due to the excessive heat dissipation which will also increase cost.

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+1 in general, but I disagree on the last paragraph. While it's true that for low dropout voltages and currents linear regulators are less expensive than switching regulators, as the dissipation increases cooling needs to be taken into account on a linear system and that can easily overtake the price of comparable switching regulator system even in cases where energy efficiency and size isn't a major concern. – AndrejaKo May 16 '13 at 4:14
@AndrejaKo Very true, but I was talking about the regulator alone, not the additional compensation as a result. I can't imagine that many people even consider heat dissipation for a simple circuit design. But I will add a note about that concern. – Kurt E. Clothier May 16 '13 at 5:27

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