how to calculate the effeciency

[hawkin]

when the input current is discontinuous, sometimes has oscillation value.
how to calculate the effeciency while run simulation, use the average current ,or rms, or integrate?
but the three results are not as same as the practical value of test board.
Is there any other method?

My product is Dc to dc chip. while the inductor current is not continuous, that problem will appear

 

[flatulent]

Use the total DC power in and out over a time period that includes a full cycle of the lowest frequency variation.

 

[nicleo]

The efficiency of DC-DC converter is not a constant, meaning it varies with load current. Usually we would like to know the efficiency of the converter when rated current is drawn.

Say a load, which draws rated current, is connected to the output of the DC-DC converter. Sample the V and I at both input and output. If n samples is measured, then

Pin = [Vin(1)*Iin(1) + Vin(2)*Iin(2) + ... + Vin*Iin] / n
Pout = [Vout(1)*Iout(1) + Vout(2)*Iout(2) + ... + Vout*Iout] / n

eff = [(Pin - Pout) / Pout] * 100

As it's in 'steady-state' operation, the proper value of n could be determined easily.

 

[hawkin]

Thanks for your response.
Of course the effieciency i mean is the value at a certain load current at steady state. So what's the problem to me is how to calculate the Iin.
Iin is a not steady value,how to get a equivalent value while in discontinuous mode(inductor current)?

 

[nicleo]

Thanks for your response.
Of course the effieciency i mean is the value at a certain load current at steady state. So what's the problem to me is how to calculate the Iin.
Iin is a not steady value,how to get a equivalent value while in discontinuous mode(inductor current)?

You are welcome.

In my opinion, 'steady state' means 'non-transient state'. Pls refer to Figure 1 at below. When we power on the dc-dc converter, the current (in inductor) needs 'finite' time (transient state) before it reaches 'steady state' operation. At steady state operation, the current waveforme can be 'ripple free' or 'with ripple' as shown in Figure one. Although there is ripple at steady state operation, the is an average value of the current, and the average value of the current will remain constant if the load is not changed.

In your situation, the current waveform is dicontinuous. This, however, will not affect the calculation of average power using the method suggested in my previous post. When the current is ZERO (discontinue), the product of V*I will be zero, so at that particular instant, the dc-dc converter does not draw current. I believe the discontinuous waveform of the current (at steady state) in your application has a trend/pattern or has a cycle/period. So, by sampling few cycles, and divide the sum of (V*I) by number of samples, we will get average power.

P/S: May be my formula has some mistakes (sometimes I'm confused when dealing with RMS or average quantity, so probably someone would help me to confirm it).