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I am designing a power supply for WiFi module. I have a regulated power supply which has rating of 17V@800mA which is for some other purpose. The WiFi Module requires 3.3V and draws maximum of 500mA current.

So to achieve the 3.3V volts there are two ways to do so

  1. To use LDO regulator which drops from 17V to 3.3V. But this is the most inefficient way to do, as it will loss much power and energy and much heat will be generated.

  2. To use Switching regulator/DC-DC Buck converter. The inexpensive modules available can do this job which much higher efficiency with very less loss of power but they will generate ripple at their output.

So, I am thinking of using Buck converter with LDO. I will drop the voltage to somewhere near around 4.3V and LDO will be added to drop further with clean output and very less ripple.

So, is it the right way to do this? Also, where LDO should be soldered?near to the controller? or it can some inches away and connected with wires for power supply?

Also the Buck converters have different frequency range, so which frequency regulator is sufficient for my need? I am considering MP1584 Module which has max. switching frequency of 1.5Mhz

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    \$\begingroup\$ A properly designed buck converter will generate acceptable amounts of ripple. An improperly implemented LDO will probably not filter the noise from a bad buck converter. \$\endgroup\$ – Wesley Lee Feb 10 '17 at 21:05
  • \$\begingroup\$ @WesleyLee Any suggestion for properly implementing the LDO to filter out noise and ripple. \$\endgroup\$ – Embedded Geek Feb 10 '17 at 21:07
  • \$\begingroup\$ My point was: if you are going to implement a buck converter specifically for the Wi-Fi module, there are probably ways of doing it so that you dont need a LDO. \$\endgroup\$ – Wesley Lee Feb 10 '17 at 21:14
  • \$\begingroup\$ A 3.3 V LDO regulator would seem to be all that is required. 5 V power supplies are so cheap today it would seem better economics to simply buy one of those. Unless you have an absolute need to be able to tolerate 5 - 17 V input due to other factors, a DC/DC buck convertor seems overkill. Though I admit the economics becomes really questionable when you can buy things like this for under a dollar: ebay.com/itm/… \$\endgroup\$ – Jack Creasey Feb 10 '17 at 21:27
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A DC to DC converter is definitely the way to go if:
1) the cost of an LDO vs DC converter makes sense (DC converters are more)
2) the energy lost in the LDO is unacceptable

There are ways to overcome the thermal limts of LDO's like paralleling them or dropping the voltage in stages (thus spreading the thermal heat across multiple devices)

There are drop in compatible DC to DC converters available that 'drop in' the same through hole footprint of a 78XX regulator . Generally the input and output capacitors will be need to be larger than a 7805. If you need lower ripple LC filters do a great job, I've been able to achieve a few mV's of ripple with these converters and LC filters.

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Do you have actually a design requirement for the ripple of the power supply of the Wifi module?

Most of the modules do have their internal logic at 1.8V, and use further LDO regulators internally. Therefore some ripple on the power lines will make no harm.

In fact, a Wifi module will draw up to 1A current peaks (it is a good idea to design for that, instead of the average power consumption of 500mA). These current peaks cause a way bigger ripples on the power supply lines than the ripple of the DC-DC converter.

It is a good idea to pick a DC-DC converter using a high fequency switching, which reduces component dimensions (smaller inductor, smaller capacitor) and usually better regulation. In case you are not experienced with DC-DC converters, you can pick a 7805-compatible switching regulator such as http://power.murata.com/data/power/dms-78xxsr.pdf

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