PhiowPhi said:
Assume a constant DC power supply, that is 30W
You have an input power of 30W from your supply, then the output power from a 100% efficient converter will be 30W.
If the output load is 5.5 ohm total, then Vo/Io = 5.5R and Vo*Io = 30W. Then Io = 2.3355 amp and Vo = 12.845 volt.
PhiowPhi said:
in my head I know it has to be 1A current since P = 30W, but if I apply ohms law... I always get higher current than 1A which can't be true, so what am I doing wrong here?
You are assuming too many fixed parameters.
You cannot change the output voltage of the 30W power supply to 30 volt without increasing the load resistance from 5.5 ohm to 30 ohm. That is because that would require more than the 30 watt power available at the input.
You should ignore power as an input parameter in your computational games.
Energy is conserved in a 100% efficient converter. Power is the rate of flow of energy.
Power is the only “computational bridge” between input and output.
Follow this computational process.
Specify the input voltage and the output voltage. Vi, Vo.
Specify the output load resistance. Ro.
Compute the output current. Io = Vo / Ro.
Compute the output power. Wo = Io * Vo.
For a 100% efficient converter. Wi = Wo
Compute the input current. Ii = Wi / Vi.
Or just note that since Wi = Wo then Vi*Ii = Vo*Io and Ro = Vo / Io.