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Switching Regulators

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debajyoty.roy

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can i connect lm2576 in series ?? I have 27 volt supply,i need 24V,12V and 5V output..so can i connect 3 lm2576 in series like 1st one gives me 24v, which feeds 2nd lm2576 and gives me 12V and so on...
 

can i connect lm2576 in series ??
To achieve what? Series circuit can make sense if the low voltage regulator uses e.g. a higher efficient synchronous topology. But if all are equal, individual 27V supplied switchers are preferred. Also expect higher efficiency due to lower current utilization of individual switchers.
 
Hi,

I recommend to supply all regulators from the same input voltage.

Klaus
 
You can connect them in series but why would you want to?
The efficiency would be worse since the 12V power would go through two regulators, and the 5V power would go through three regulators.
Thus, for example, if the regulator efficiency were 90%, the 5V efficiency would be only 0.9³ = 73%.

Also the 24V regulator would have to handle the total power, not just the 24V power.
 
Thanks for your reply,actually what i think is, if the regulator which gives 5v output,its better to give it 12v input rather 27v input for achieving better efficiency and wasting much less power.please suggest what should i do??
 

Hi,

what i think is,
Why do you think this?
Read the datasheet and you can be sure.

Take a pencil, a sheet of paper and a calculator.
Then go through your design and calculate the values you are interested in.
Then we can talk about it.

Klaus
 
Thanks for your reply,so you suggest that all regulator should have 27V input.So which is better option for 5V volt regulator, 12V input from previous regulator or 27V individual supply??and which is more efficient??
 

The question has already been answered. If all switchers are LM2576 type, direct conversion 27 to 5 V gives higher overall efficiency. If you have a high efficient 12 to 5 V switcher, series connection might be slightly better.

You can check by looking at the datasheet efficiency curves. Direct conversion 27 to 5 V gives about 80 % efficiency, double conversion 76% * 87% = 66%.
 

i connect 3 lm2576 in series like 1st one gives me 24v, which feeds 2nd lm2576 and gives me 12V and so on...


It is not better idea to proceed with. So keep the 27V as the input supply voltage & derive the required 24V, 12V & 5V from it.
 

...So which is better option for 5V volt regulator, 12V input from previous regulator or 27V individual supply??and which is more efficient?? ...

Please try some homework; look up the datasheet and calculate the efficiencies for the two cases you have mentioned.
 

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