# Calculating Efficiency of a circuit

I made a boost converter, and now I want to calculate the efficiency of my circuit. I know the formula to calculate the efficiency which is given by

$Eff = \frac{P_{Output}}{ P_{input}} \cdot 100\%$

where $P_{Output}$ is the Power at the output and $P_{input}$ is the Power at the input. But, I am confused at the output stage. At the output stage, the Load is connected, and power depends on the connected load. Which means that there will be different efficiencies for different load. Is this right? Can I just use a normal resistor as a load?

Also, when you make a circuit, what are the major tests you need to perform and check? I mean like efficiency test, thermal test, Emc test, etc.

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Efficiency for power supplies is most meaningful at full-rated load. Without a load, the output power is zero and therefore efficiency is meaningless. If you look at the data sheets of a lot of switching converters they'll show graphs of efficiencies versus various loads but they will never really small or zero power loads BUT they will always show full-load power efficiency.

Also when you make a circuit what are the major tests you need to perform and check? I mean like efficiency test, thermal test, Emc test, etc.

For a power supply, efficiency is important for a lot of designs and I always run a regulator circuit at full load at elevated temperatures (above what it can be expected to see) because, with little doubt or uncertainty, the most common failure of components is in power supplies. EMC can mean many things and I think that unless you are designing a power supply to be sold as a power supply, EMC testing would be done on the whole product.

I would also look for ripple voltage problems and instability issues on various loads.

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You designed your boost converter for a maximum output current. Divide the voltage by that current and find out what resistor to connect as a load. The power of the resistor should be greater than the voltage multiplied by maximum current.

Use a voltmeter and test the voltage. If it has dropped, then it is clearly that you converter doesn't support the maximum amperage it was designed for. Also measure current. If it is the case for the voltage to drop, this would be the maximum available current. Multiply this by the measured voltage. This is the actual output power.

This can also be used as a reliability test. Deliberately connect a resistor that will draw a greater current than the maximum, and see how your converter performs (if it gets hot, measure ripple etc.).

there will be different efficiency for different load, is this right?

Yes, but the load shouldn't draw all the maximum available current. You design your converter for an output power of 5-10 % greater than the maximum load.

This can't be considered the efficiency of your boost converter. It is the efficiency of your entire circuit.

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