48V to 5V @ 500mA buck converter

[alzomor]

Hi,

I need to implement a 48v to 5V buck converter.
the load is 500mA.

I found some docs preferring to use isolated converters for high input voltage in the range of 48V.

Is it a must to use Isolated converter?
and what's the drawbacks of using non isolated converters?

The space available on the board is very small, and that's why I prefer the non isolated converter.

Best Regards
Hossam Alzomor
www()i-g()org

 

[IanP]

Is it a must to use Isolated converter?

No, it's not ..
If there is no special reason to separate grounds between 48V-section and 5V-section, normal step-down converter should work fine ..

IanP

 

[alzomor]

and what could be the special reasons?

 

[IanP]

Problem with ground such as ground loop ..
Dirty/noisy power ..
.. e.t.c. ..

 

[shirsanka]

Re: 48V to 5V @ 3A - converter [Automotive grade]

Check it; its very stable and different.

 

[spiralbrain]

LM2575HV is a chip from National that can do it with minimum components

 

[eem2am]

what is tolerance on the 48V?

to my mind, 48V is OK and within the SELV regulatroy requirements..

i though it was 60VDC that was considered dangerously high, and therfore needing isolation.?


even when you go into companies, you will find that no-one knows the SELV levels......i have never found it on google either

 

[eem2am]

anyway, go for synchronous buck as you have low duty

 

[techie]

LM2575 is a low efficiency device. So if efficiency is not your concern, you can go for it. There are other options as well
LM2596 is a similiar device with some improvement in efficiency.
You can use a current mode regulator like SG3842 with an external MOSFET to get better efficiency.
For best result, as eem2am said, use a synchronous buck since you have a low duty cycle and the flyback diode in will be conducting most of the time if you use non-synch

 

[spectrum17]

Hi,

I need to implement a 48v to 5V buck converter.
the load is 500mA.

I found some docs preferring to use isolated converters for high input voltage in the range of 48V.

Is it a must to use Isolated converter?
and what's the drawbacks of using non isolated converters?

The space available on the board is very small, and that's why I prefer the non isolated converter.

Best Regards
Hossam Alzomor
www()i-g()org

Hi Alzomor,

You can choose one of this controllers from TI,I hope this will help you with this **broken link removed**.

rgds,
spectrum17

---------- Post added at 07:26 AM ---------- Previous post was at 07:17 AM ----------

Here's another non-isolated controller but Vin(max) is limited to 40V.Hope this will helps.

https://focus.ti.com/lit/ds/symlink/mc33063a.pdf

rgds,
spectrum17

 

[alzomor]

I found a good system on chip from Mornsun

salam
Hossam Alzomor
www()i-g()org
**broken link removed**

 

[altenergy]

Hi guys, i am new to this forum and most others, so i must say another great forum to help others.
I also have a need for a switchmode converter from 48V. i need a diagram for a 48V (max 60V fully charged) to +12V and - 12V Isolated switching converter. It is to be used with my solar and wind power MPPT controllers. The current required is only about 100mA max, as it only supplies 6 op amps. It has to be isolated to avoid shorts and ground loops. So i only need a diagram for the power supply section like Alzomor, but space is not so much of a problem. I am OK with linear supplies but not switchers. I could probably tap +12V off the +48V battery but of course not the -12V. I could get away with -5V also. I have seen the diagram posted using LM2575, but this is not isolated.

Regards
Leon

 

[dick_freebird]

I bet some of Vicor's new postage stamp sized DC-DCs
would be a whole lot easier than rolling your own.