how to step down 50v efficiently ?

[aliyesami]

I have a 5.2Amp powersupply 50v . I want to get 5v or 3.3v voltage sources out of it (among other LDD drivers I have connected ) .
I have been talking to digikey and they cant find a way to step down from 50v to 3.3v or 12v.

on ebay the chineese are selling exactly what I want but I want to make myself this converter .

**broken link removed**

thanks

 

[Now_and_Zen]

How about TPS54560, this design is about 84% efficient:


You could use an LDO regulator to get 3.3v from this 5v out. Do you actually need 5A of current at 5v/3.3v?

 

[aliyesami]

How about TPS54560, this design is about 84% efficient:
View attachment 103064

You could use an LDO regulator to get 3.3v from this 5v out. Do you actually need 5A of current at 5v/3.3v?

hi Zen!

thanks that was great help and no I dont actually need 5A for 5v. I have LED drivers connected to this powersupply and i want to just piggyback on the same supply for my processor board.
for processor board i have only one atmega1284p, one TFT display and an RTC and keypad encoder , all 3.3v low power devices so i am thinking I wont need more than 500mA for them .
so my question is can we change your supply circuit to draw max 500-700 mamp ?

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also wanted to ask if the above circuit is rated at 5A , does it mean the chip is drawing 5A or does it mean that the power supply can supply 5A max?
if I connect my microcontroller board which only requires say 500mA , it will draw 500mA and not 5A right?

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what if I use this chip LM2575HVT-12/NOPB-ND and put an LDO to get 3.3v , this was I will get 12V also to drive the two low power fans ,70mA each ?

 

[Now_and_Zen]

5A is the maximum current it can supply, with smaller loads it will draw less current from the supply - it will happily work at 500-700ma. Here is the efficiency curve for it:



So, it is still around 80% efficient at 500ma.

if I connect my microcontroller board which only requires say 500mA , it will draw 500mA and not 5A right?

It will deliver 500ma, but it will draw considerably less than 500ma from the supply because the voltage is much higher - probably draw 60 or 70ma from 50v supply.

If you want a design to give 3.3V at 700ma try this:



If you want to try different options then go to www.ti.com and try their webench simulation program, you will need to register on the site but it's free. It is easy to use and very good but obviously only offers solutions using Ti parts.

 

[aliyesami]

thanks a lot Zen , you fixed my issue.