[SOLVED] LDO or switching regulator what to use

hi all,



am confused whether to use an linear regulator or a switching regulator. my input is an 24v power supply from an smps , my output reguirements are 5v 100ma max. am confused whether to go with a linear or a switching regulator as linear regulators dissipate more heat , but the advantage is less cost and no isssues about EMI, but if i go with an switching regulator its efficient but bit costly and have to deal with emc issues.please advise


Thanks in advance

(24V-5V)*0.1A=1.9W

If you have to do without a substantial heat sink, this
may force you to a switcher.

There are many outfits now selling "micromodule"
switching regulators which may be more EMI-benign
(due to much smaller current loops and careful design)
than board-level implementations. But what "emc
issues" means to you, and your friendly neighborhood
compliance oversight agency, I couldn't say.

These are the sorts of decisions that every designer must learn to make, and be able to defend his/her choice depending upon the application.
It is good that you know that there will be wasted energy (heat dissipation) of 1.9Watts - in some cases this may be acceptable, and in other applications, not. For example, if I am making a circuit for an audio or other small analog signal filter or gain block that I wish to be very, very clean (no switching harmonics from power rail) for precision sensing, I might choose to be wasteful in favor of possibly cleaner power for my analog circuit with the LDO. Or if this is for a cheap, inexpensive device that will be produced in the millions and I have an adequate heatsink to use and saving the cost of an inductor is a big deal, I may choose the LDO. But, if I need to be energy conscious (battery powered devices) and maximize the run time of the unit before the battery needs to be replaced, or the price of the added circuitry parts for the switcher circuit is small compared to the price of the product, I may choose the switcher. EMI is another valid argument for some applications, and other applications it may be of little consequence. Heating of adjacent parts, overall product reliability are other valid arguments, too.

In many cases, there can be a perfectly good set of arguments for either choice, and either is fine. But in other cases, there are clearly stronger arguments for one over the other. Since we don't know what this thing is powering in your design, I cannot definitively say which choice is better.

In general though, if your design/application will support it and without knowing anything else, I would recommend using the switcher just to be more energy conserving or environmentally conscious, and to provide the learning opportunity. If you tell us more, perhaps we can help you decide.

In any case, this has given you something to think about.

Note that for such a large voltage difference between input and output, an LDO (Low Drop Out) regulator has no advantage over a standard (e.g. LM317) regulator.
They both will dissipate the same power.

Proceed with by using Switching regulator and follow the steps to work on EMC issues.You can try to make it by using smart PCB layout techniques. New switching regulators EMI radiation is smaller. Most of the EMI is from the charge/discharge in the feedback loop. So, it is important to get the layout optimize.
•Large ground planes to take all that current away.
•Parallel traces/caps to ground in order to cancel noise and EMI.
•You can also shield your converter to prevent noise to nearby elements.
•If you have large Inductor, you might want to consider placing another one on the opposite side of the PCB to cancel the noise/EMI it can cause.
•You can use also Ferrite Beads to get rid of some of the EMI.

SWR will be better. With LDO, you need to provide heat sink for (24V-5V)x0.1A=1.9W power.

thank you all , decided to go with a switching regulator