Electronic – Choosing a linear regulator vs. switching regulator for low-power application

A UBEC (Ultimate Battery Elimination Circuit) is basically a step-down voltage regulator. I feel that the jargon deserves a bit of explanation and history, so here goes:

In hobbyist grade remote control cars/planes/boats/etc. the electronics (receiver, speed controller, servos) need a power source. With engine powered craft, a small 6V battery pack was used to power the electronics. When electric motors became more popular, people wanted to use the large motor battery packs to power the low-power electronics. Typically, the electronic speed controller absorbed this function, and it became known as a Battery Elimination Circuit (BEC). With battery packs usually in the 9V-11V range, the electronics would probably need 5-6V to be happy.

Evidently there has been a push to use higher voltage battery packs (10V-25V), probably to take advantage of the brush-less motors. As a result, if the servos draw any appreciable current, a linear regulator would burn a lot of power. Obviously, when your flight/driving time is based on how efficiently you use your battery, a linear regulator is not what you want. Ultimate Battery Elimination Circuits are basically separate regulators (usually switch-mode) that deliver 5V-6V at hopefully high efficiency.

Now for the comparison. Your parts basically have two different end-use requirements. The Dimension Engineering product tries to match the form factor of a common linear regulator (7805). It would probably integrate better with any finished PCB you would make, and has a metal shell which hopefully shields EMI. The Hobbywing regulator is a more cost-conscious physical design, with a bit better efficiency spec. Honestly they're pretty much the same thing, so you could probably go with the cheaper one (Hobbywing).

My load current for the 3.3 V rail is 546.2 mA. My load current for the 1.8 V rail is 1.154 mA.

Your 1.8V rail is basically just a reference voltage. A voltage divider from a regulated source would work just fine. A 1.8V 1.154 mA load is like a 1500kΩ load, keep that in mind when you make your voltage divider. Efficiency isn't really an issue here. Even at 50% efficiency, that's 4mW.

As for the 3.3V rail, with a 3.6V battery, likely a lithium battery, you want a buck-boost switching regulator, as the voltage range of the battery will be above AND below 3.3V. You want it to regulate down, and then regulate up. Look for one based on your battery chemistry, as there are some that have built in battery protection, to prevent it from draining too low.