[SOLVED] QUICK simple question about input current

[bowman1710]

Sorry for such a simple question, but if you have a power supply with say '24V output at 200W with a 16-20V input'. How do you know roughly what the input current needed will be? Is it the power required divided by the input voltage?

 

[KlausST]

Hi,

we con only guess.

it is a step up conversion. Maybe by the use of boost converter ICs.

then: Pin = Pout / n
Where n is the efficiency.
Lets say it is 80% then the max input current is:200W /(80% * 16V) = ???

Klaus

 

[bowman1710]

Thank Klaus, I did this but didn't take into account the efficiency. So it would roughly take between 12.3A and 13.8A depending on efficiency but the output current would only be 4A. So for a boost converter the inductor would have to be rated at least 14A then?

 

[schmitt trigger]

The inductor should be rated for the maximum average input current, plus half of the calculated ripple current.
This is usually set about 30% of the input current for CCM, so we are talking about 18 amps.

 

[KlausST]

Hi,

just an addition to schmitt triggers correct suggestions:

there are two current values for inductors you have to take care of.
* one is the DC or RMS average current. This is the value for power loss and heating. To go beyond this limit will burn the inductor winding.

* the other is the saturation current. It is a peak current. To go beyond this limit the inductance decreases and the current rise increses within us.
this generates high EMI and may cause regulation instability.

Klaus