# What is the meaning of zero voltage switching (ZVS) and zero current switching (ZCS)?

I was reading about induction heating circuits in a electronics textbook and saw the terms ZVS and ZCS which are abbreviation for Zero Voltage Switching and Zero Current Switching respectively. There are many academic articles about these topics, but for a novice like me these articles are very theoretical and i can't get a grasp of topic. I would be happy if someone could help me and explain the idea behind ZVS and ZCS.

That's actually pretty simple:

In many situations, you need to switch a load on and off – for example, to dim a lamp.

It's often advantageous to switch something when either the current flowing is zero, or the voltage across the load is zero.

Now, if your load is a pure resistance, then the point where zero current flows is exactly the point where zero voltage happens.

But for things like inductive or capacitive loads, that's not the case – current and voltage are out of phase for these kinds of loads.

The motivation to do something like switching a load when the current is zero is that this means you don't get $\frac{\partial\,i(t)}{\partial t}\rightarrow \infty$ that you'd get when switching off something when a current is flowing. And because of the physical laws, having a high $\frac{\partial\,i(t)}{\partial t}$ in an inductor is very bad – because it will cause a voltage peak of a very high amplitude!

• ...resulting in the counter-intuitive result that the best time to switch a pure inductive load is at peak voltage! – Ian Bland Nov 25 '16 at 15:49
• @Ian Bland- By peak voltage, do you mean the back emf? – Vinit Shandilya Nov 25 '16 at 16:22
• SMPS should get mentioned here. I've seen buck converters in the 99% efficiency range. – user110971 Nov 25 '16 at 17:07
• @VinitShandilya at the peak of the supply. The current should be passing through the zero point (ideal model) at that instant. – Ian Bland Nov 25 '16 at 18:57

Terms Zero Voltage Switchingand Zero Current Switching are very unfortunate and misleading. More appropriate terms would be Zero Voltage Turn-on and Zero Current Turnoff.

The idea is pretty obvious: for the switch itself it is advantageous to be turned on a tad before there will be current through it, and turned off when current is already ceased.

• Zero-voltage switching can be done at turn on or turn off so there's no problem with that expression but I'll agree that zero-current switching doesn't make much sense in the off to on condition. – Transistor Feb 9 at 13:24