For a switched-mode power supply, can volt second balance be applied to capacitor voltages too at different operating modes or is it only restricted to inductors?
Is it technically correct to express capacitor voltages in terms of the inductor, so as to apply VSB?
Please explain in detail!
Hi,
In reference to switched mode converters, you cannot apply volt-second balance to capacitors. For capacitors, we have "charge balance" or "current-second" balance relations. you can google and read up more about that.
"Is it technically correct to express capacitor voltages in terms of the inductor, so as to apply VSB?" I don't think so. But if you could be more precise in what you mean, it would help.
Dear P. Arvind, volt-second balance can only be applied on inductor because during one sampling time, average voltage across the inductor is zero in a steady state condition. However, average voltage across the capacitor during one sampling time is not zero in steady state condition. That's why volt-second balance can not be applied on capacitor.
No, it is not technically correct because the behavior or response of inductor and capacitor voltages are totally different from each other.
The volt-second balance can not be applied to capacitors. For capacitors, we have "charge balance" or "current-second" balance relations. However, it can be applied to inductor. As, response of inductor and capacitor voltages are totally different from each other.
Afaq Hussain thanks for nicely putting it up. As an additional understanding exercise, would recommend you, P. Arvind, to study the waveform of current through the inductor in an SMPC device. You will see, that during one mode (ON/OFF), the current rises and during the other mode, it falls down. Now, in steady-state, the average current through an inductor is constant. This means, the amount of rise and fall of current in the two different modes should be equal in magnitude, thereby canceling the overall change in current. Note that the rise and fall of the inductor current would be equal to the rate of rise multiplied with time of rise and rate of fall multiplied with time respectively. But, we know that rate of rise/fall of inductor current is proportional to the voltage across the inductor. So basically, the product of voltage across inductor during ON mode and rise time, and the product of voltage across inductor during OFF mode and the fall time, add up to zero, in other words, "Balance" out. Hence the name, inductor volt-second balance. Now, it is important to note that this 'balancing-out' happens only in steady-state when the average current through the inductor is constant. It might interest you to know, that during the transient state, inductor volt-second balance is not a valid phenomenon. I hope this helps. Thanks for reading.
volt second balance can be applied. you can use other methods available
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