Here main focus on ac-dc and dc-dc converters and reference to these devices this component is used for transferring energy from one level of voltage to other level of voltage. it is used mainly in buck ( forward), buck-boost(flyover) and boost converter. when switch is “ON” it store energy and when switch is “OFF” it releases energy.

Von=L delta Ion/ton(current increases); Voff=L delta Ioff/toff(current decrease) ;

It must be delta Ion=delta Ioff i.e current level at the start = current level at the end, otherwise no steady state or no repeatability. swinging component of inductor current is completely determined by the applied volt second and inductance.

core loss

core losses do not depend on the dc pedestal of current I, only on the swing in current i.e peak to peak current swing—>delta fie.

PFC inductor swing

under each condition, the current swing is so different that it seems impossible to estimate the core losses or even their average value, for better estimate of temprature rise of choke.

energy storage n inductor

it is B squire/( 2 mue) per unit volume =I squire x L/(2) per unit volume

air gap increases core volume enable the core to store more energy.

inductance

N squirex mue xcross section area/length

Transition analysis of buck converter.

1). prior of switch ” ON” diode is carrying obviously carrying the full inductor current. Then the switch is start to turn ON trying to share some of the inductor current. Therefore diode current must fall correspondingly.

2) The important point is that while the switch current still in transit, the diode has to be able to pass some current( the remainder, or left over amount of the inductor current). but even to to provide some of the current, the diode must remain fully forward biased.

3) Therefore nature (i.e., induced voltage in this case) forces the voltage at the switching node to remain below ground- so as to keep the anode of the diode above 0.5 V higher than the cathode.

4) As per kirchoff’s Law the voltage across switch stays high. Only finally when the entire inductor current has shifted to the switch , does the diode “let go.” with that the switching node is released , and it flies up close to the input voltage- and so now , the voltage across the switch is allowed to fall

conclusion : we therefore see that on turn on the voltage across the switch does not change until the current waveform has completed its transition, we thus get a significant V-II overlap.

Turn Off transition

for the switch current to start decreasing by even a small anount ,the diode must be ” positioned ” to take up any current coming its way. so the voltage at the switching node must first fall close to zero so as to forward bias the diode. that also means the voltage across the switch must first transit fully, before the switch current is even allowed to decrease slightly.

we therefore see that at turn off , the current through the switch does not change until the voltage waveform has completed its transition .

Fundamental properties and behaviour of the inductor ,are ultimately responsible for significant overlap during cross over.