I am designing a WiFi based home automation module and for that I have a regulated power supply which has rating as follow 18V @ 1A. Some device is connected to that which draws around 700mA of maximum current at 18V.
I need to attach ESP12 WiFi Module to it as well. I have checked the ESP12 datasheet it doesn't require current more than 200mA, but supply has sufficient current to drive ESP12.
Now my question is what is the most reliable and efficient way to power ESP12 module from the power supply I have (18V@1A) ?
In my opinion, a dc dc converter like LM2596 or MP1584 or MP2307 or ST's L7980 are some of the decent dc dc converter IC which can solve the purpose. They can provide decent current and has wide range input as well.
But I have read that, a good 3v3 linear regulator fed from, say a 5v supply provides more reliable results than a 3v3 switched-mode supply. For example LM1117 which produces 3.3V
Also, I read that these converters occasionally reset themselves down to about 1 V output!
If I go with above DC DC converters which one I should go with, all has different switching frequency and almost same output current. Any recommendation on that?
Best Answer
Sure, along with literally thousands of other switching regulators that may or may not be suitable. To get the best performance and efficiency, you have to make trade-offs between footprint size, cost, heat dissipation, useful features, product availability, power needs, inductor selection, and EMI considerations (just to name a few). Furthermore, the layout design of the power supply on your PCB or (god forbid) breadboad can have a big impact on performance.
However, if you're designing this for a one-off hobby project, any switching regulator that meets the basic requirements (Vin, Vout, max current, etc) will probably be fine. Also, don't forget that if the ESP8266 draws 200mA at 3.3V, that's only about ~40mA from an 18V source. You can get away with much smaller regulators than the ones you mentioned in your question.
There is a technique in power supply design to use a linear regulator as the last stage of a voltage conversion circuit to minimize ripple. Switching regulators can be very efficient, but will produce ripple on their outputs. The ripple is an unavoidable consequence of the topology of switching circuits. The ripple can be mitigated with capacitors, but sometimes adding more capacitors to the output may not be practical. Linear regulators are typically inefficient, but have very clean outputs. The idea is use a switching regulator to do the majority of the voltage conversion (up or down) and then use the linear regulator to drop the last little bit. In this way, you get the benefit of the clean linear regulator output and minimize its efficiency loss. Here are some examples of different configurations, assuming a 90% efficiency for the switching regulators. You can see that combining the two types of regulators is a good trade-off between output quality and power losses:
simulate this circuit – Schematic created using CircuitLab
More than likely, what you were reading about was a case of a regulator reacting to a over-current or over-temperature condition. Many modern ICs will shutdown to save themselves in such conditions, but that's not unique to just switching regulators. And it's a good thing to shutdown rather than overheat and catch fire! Regardless of what you read, a well designed voltage regulator will never just "reset" itself for no apparent reason.