From mains: PFC+buck+LDO. Best solution.

thank you for your answer, what is the function of using PFC circuit to produce adjustable current DC output?

Thank you for the answer, i really appreciated it

First you must decide the input voltage which is greater than (or) less than the output voltage.Then based on this you select buck ,boost (or) buck boost converter.The current rating is based on input power and select appropriate device to with stand current and voltage.

Hi guys. There are many different solutions for your question. in addition to that proposed by Sivaraman Pandarinathan, can also consider a half bridge or a full bridge DC-DC converter: these two converters will also ensure the possibility to work with negative currents (for example in the case of DC or PMDC electric motors in braking phase). to limit the current to a certain value you must, however, work with the control, by setting instead of a PWM control with hysteresis current. Find all the details on the English version of Power Electronics Mohan et al.

Power Electronics by Mohan, Undeland and Robbins.

I strongly recommend you to go with Flyback resonant converter [DC/DC Converter].

I used this converter for aerospace application [sponsored by leading main Airframe company in France, UK and Germany - EADS, AIRBUS].

Power in DC circuit product of voltage and current,so if you have enough input power then we get required voltage and current.Refer Hand book of power electronics by M Rashid.design procedure for buck, boost,and buck -boost converter avilable.The DC-DC converter act as a variablle DC transformer

PFC is for smoothing the asimetric load usualy applied by a powerful enough power converter to mains and so is for avoiding the usual perturbation caused by this kind of load to the almost sinewave variation of the mains. This perturbation not only it is forbiden by some regulations but can cause self reseting of other loads (PCs for example). This block can be omited in a less complicated converter.

Hallo, if I understood your question right, at first I think you have to decide what is the supply voltage of (for the converter), is it AC or DC, so that you can decide using an AD/DC- or DC/DC-Converter. Next point is it, to look at the kind of using e.g. do you want to use it in medical environment or not (take a look at isolation voltage). Then you have to check whether your voltage or current has to be constant and do you need a linear or switching regulator to create a fixed 20Vdc, 5A output. Use linear regulator for less noisy output and analogue circuits.

If your load needs different current values over time and your current can be greater than 4.7A , you should create a stable 20V fixed output which can deliver 6A or more, that your regulator is running at 75% power, good for longtime usage.

If voltage has to be fixed, you can also find different power supplies on the market (EMTRON, RSOnline, Farnell, Digikey…) or you design a converter by your own. To do so, download LTSpice and search for suitable regulator and try to check for a component that goes along with a macromodel. If you want to find more components use alldatasheet.com to search for other regulators.

Power Electronics by Mohan, Undeland and Robbins

Also refer Mohmad Rasid

you have not mention input voltage magnitude. If your Input is 20 V than buck-boost converter and less than this then boost otherwise buck converter

What is the input voltage?

You can refer to this book:

Power Supply Cookbook, Second Edition (EDN Series for Design Engineers)

Firstly tell me what type of supply voltage you are giving A.C.or DC??? If input voltage is ac then use ac-dc converter. The converter should be controlled type.If the input voltage is dc then use dc-dc converter ie buck-boost converter. My suggestion is that firstly observe the output in MATLAB simulink or LABVIEW.then go for hardware. Please, tell me in which area you are going to apply this converter.

20V @ 4.74A means you are driving a Lenovo laptop computer (my X220 has exactly those numbers on the nameplate) or something very similar. Lower voltage source means you want to use an automobile 12V system or something very similar. The mentioned flyback converter is a logical choice. You could also use a DC:AC inverter and plug the laptop charger into it. That way you have AC power available for other things, and it's an off the shelf solution.