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DC Circuit Breaker Selection

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stoui333

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Hi,

I have the below block diagrams as an example.

Drawing1.jpg


Question 1: Circuit breaker should be placed on the input or on the output of the DCDC converter ?
I suppose both will work but whats the effect in case of a short?

Question 2: How do i calculate the circuit breaker amperage selection?
Question 3: The estimate power consumption should be the peak or average for the circuit breaker selection?
Question 4: In order to calculate the estimated Peak power consumption of multiple boards/units/modules i sum all peak power consumption values of there datasheets and multiply my a safety % factor?
Question 5: How to avoid circuit breaker trip from in-rush & surge currents?

Thank you,
stoui
 

Hi,

Many DCDC converters have integrated current limiters.
Thus, maybe one does not need a circuit breaker at all.

If you want to add an external circuit breaker to a DCDC converter with integrated limiter, it will be difficult to choose the correct value.
It is very likely that the circuit breaker never will trip --> what makes it useless...a waste of money.
(A DCDC converter with short circuited output may draw low input current while delivering full output current)

The datasheet should give informations.
If not sufficient, then look for design notes, application notes, and other documents provided by the manufacturer.
If still not sufficient, then contact the manufacturer.

Klaus
 

Hi,

Thanks for your reply.

The DCDC has no integrated current limiter.

Not sure how this statement is valid "(A DCDC converter with short circuited output may draw low input current while delivering full output current)"
Could you elaborate a bit further?

Thanks
 

Hi,

let´s assume you have a 5V 1A output DCDC converter.
At full load the output power is 5W. and with (let´s say) 90% efficiency this means it draws 5.566W of input power.

Now let´s say the output is short circuited.
The out voltage is low. Thus the putput power is low, even at full 1A of current.

Depending on circuit ... it´s possible, that the DCDC draws only 1W of input power. this is less power than not short circuited.

****
The DCDC has no integrated current limiter.
Click to expand...
But in picture of post#1 is says: "With overcurrent shutdown protection". --> so what does this mean?


Klaus
 

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