I have a supply of 17V@890mA. I am using COTS DC-DC converter, which has efficiency upto 90% at Minimum input voltage and 83% at Max Input voltage. It has input range between 4.25-24V. It provides output at 3.3V@1A.
So what will be the current consumption/Input current requirement of this converter? On what factor it depends?
I couldn't find this info in the DC-DC converter specs.
The factors that determine input current are output power, input voltage, and converter efficiency. Power = Voltage x Current. Efficiency = Power Out / Power In. If you know the converter's efficiency at the voltage and power it is operating at then calculating the input current is trivial.
But...
...which has efficiency upto 90% at Minimum input voltage and 83% at Max Input voltage
That's a problem, because it only tells you the maximum efficiency the converter can achieve, not what it will be at any particular operating point. Efficiency typically peaks at less than rated output current. Here's an example:-
Pololu 3.3V, 1A Step-Down Voltage Regulator D24V10F3:-
At 5V this converter's efficiency peaks at ~93%, but is down to 83% at 1A out. At 24V it peaks at 83%, and is down to 79% at 1A. At 17V we would expect it to achieve about 81% at 1A. Now we can calculate the input current.
3.3V x 1A = 3.3W out. 3.3W / 81% = 4.08W in. 4.08W / 17V = 0.24A.
