PierreJ said:

Hello friends I am Pierre living now in UK.

I tried to use many times ltspice and get joy never.

Even going to very basic circuit nothing ever do that it real would in

world. [...]

Why v(n002) not go very minus at 1ms?

I asked of engineer friend why but he refuse to look but say

"simulators suck" and refuse to discuss further more.

TIA

P.

The sim is working perfectly and shows a true picture of the inductor

current.

Node 2 correctly goes as minus as it can go. I.e minus 0.29V.

To get numbers, use the standard inductor formula ...

Amps per second through inductor = Voltage across it / Inductance.

At 1mS when the pulse cuts off, there's about 100ma flowing through the

inductor and it has some potential energy stored in it's magnetic field.

(stored joules=1/2 x L x i^2)

The inductor's magnetic field starts to collapse and will try force a

current flow through -any- circuit path.

Any obstruction and the current will force a voltage across it. In this

case there is only the diode still in circuit and this will drop 0.29V at

the discharge rate.

We've fixed the inductor voltage at about 0.29V (the diode) , have an

inductor of 0.1H, so collapsing field current through the inductor flows at

a rate of 0.3/0.1, or 3Amps per sec. Which is a drop of about 4.5ma in the

1.5mS before the next 'charge' pulse come along. (the spice correctly shows

this)

Notice that the magnetic field and circulating current are seemingly taking

ages to drop off. This is because there is little energy being burnt off by

the diode and this is comparable with the energy stored in the inductor .

(Noticeable in real life when a diode protected relay coil is switched off

and the relay hesitates before opening).

If you want node #2 to be quickly discharged then from the inductor formula

it's simply a case of adding lots of resistance in the inductor discharge

path. I.e a high resistance, equals high voltage, equals high power loss.

The power can only come from that stored in the inductor's field and like a

battery will quickly flatten. The real life case is a relay coil -not-

protected by a diode. Or an inductive coil with say a 30V Zener across it,

or a voltage step up power supply, etc.

These simulator thingies are handy. Your friend is missing out.

john