For example, SMPS in our mobile phone charger. When frequency gets increased, Skin effect and Proximity effects comes into the act. Also, harmonics gets added which could still bring down the efficiency. Core losses also plays a considerable role. Yet SMPS is efficient than conventional chargers which uses normal step down transformer. Here what makes that difference other than frequency?
Basically, some losses increasing with increment of frequency such as core loss, switching losses, the other losses reducing with the increment of frequency such as conduction losses. In a frequency versus losses plot, the two kinds of curves will meet at one point, that should be the optimized frequency. The total loss will be minimized at this frequency.
So, if you select one frequency smaller than the optimized frequency and compare the circuits with the circuits for optimized frequency, you will have same the observations as mentioned in your example. However, it does not mean that the higher frequency always leads to higher efficiency.
As Mr.Wang mentioned , if we design any converter at optimized level of switching frequency , we can see improvements in the converter performance like efficiency .
Basically , if we design a transformer for the same power with low and high operating frequency , we can find difference in the power loss of the transformer . Under higher operating frequency , we have options to bring down the conductor loss by using less number of turns and using flat or foil type of conductor instead of solid conductor by taking care skin effect .
Also by using higher operating frequency , we have options to bring down over size of the transformer where the over all core size will come down . So there will be reduction in overall core loss /Kg .But if the frequency goes above certain range , there will be increment in the other part of core loss .
Regarding switching devices , when we aim for higher operating frequency , there are devices with low ON state resistance with higher operating frequency . So we have options to reduce devices conduction loss . Also when we use improved topology like soft switching technique , we have options to reduce switching losses even at higher switching frequency .
So as per my understanding , it is all bout the use of suitable topology , use of advanced devices and optimization of converter operating parameter like frequency by which we can well differentiate the SMPS design from conventional converter design in various aspects . Hope my inputs will clarify your query . Thanks .
High frequencies can only handle signals not power. So, it is very difficult to design power related appliance working at very high frequencies.
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Modern Cool technology devices have low on state losses and can operate at high switching frequencies. Switching losses across the power semiconductor devices can be minimized and ideally bring down to zero using zero voltage or zero current switching topology. High frequency reduces the transformer core size drastically with only fewer turns in either side. Special magnetic cores with high resistivity (reduces eddy current loss) and narrow magnetizing loop (reduces the hysteresis loss) reduce the core losses. Thus you can finally scale down all the losses, albeit with increased cost, but end up with more efficiency.
Higher frequency comes with
- conduction loss - no change
- switching loss - increase
- core loss - depends, can be decreased
- winding loss - depends, can be decreased
so there's a trade-off between switching loss and magnetic components' loss. A good magnetic design can reduce the loss significantly. Thus the total efficiency can be increased accordingly.