## Saturday, 29 December 2012

### Inductor Voltage Rating

Have you ever wonder that when you read through datasheet for inductors, you rarely see the voltage rating?
Shown in picture below are some common inductors seen.

The fact is, inductor does have voltage rating, the winding wire have a fix thickness of insulation coating, if high enough voltage is applied across the inductor, although momentary and the current is within the specification limit, the insulation will breakdown and short to adjacent wire. From personal experience, normally inductor voltage is about 60V, unless specifically stated in datasheet. Maximum voltage allowed is usually depends on insulation thickness of wire used, and whether the windings overlap.
If you does wonder whether your inductor has insulation breakdown, the easiest way is to measure DC resistance, depending of actual short, the resistance will be a lot or somewhat lower than a good one. Alternately, if you have a LCR meter, you can use it to measure the inductance instead, in this case, expect faulty inductor to have lower inductance (less winding over the magnetic core).

## Saturday, 22 December 2012

### Real Life Inductor : When Does An Inductor Stop Behaving Like One

1. When current is too high – because of magnetic saturation
2. When signal of interest is of too high frequency – higher or near inductor self resonant frequency. There are parasitic capacitance across inductor winding  so in a way, we have parallel LC circuit, at high enough frequency, the impedance of C will gets low enough to shunt out the impedance of inductor.

## Friday, 7 December 2012

### What does SCR protection circuit has in common with reactive armour tanker?

SCR is a circuit component that conduct when it is been triggered. typical circuit is as shown below:

When there's overvoltage across Rload, zener Z1 will conduct and trigger SCR X1 into conduction - this cause huge current that blow the fuse.

Without this protection, the current level during over voltage might be too little for fuse to burn open
Now compare this protection mechanism with explosive (reactive) armoured tank shown below (picture from http://en.wikipedia.org/wiki/Reactive_armour).

Those “bricks” are actually explosive material. When the tank being hit by bazooka, the plate will explode, thus dispersing the piercing force of the bazooka, and thus preventing injury for personnel in side.

Both SCR protection (with fuse) and reactive armour protection work in similar way – namely by conducting large amount of current to burn fuse versus exploding of “brick” to disperse piercing force of bazooka– to protect the cargo, by preventing the destructive force from 'hurting’ the cargo.