Inductive loads

[Asjad]

Hi All,

IS it true that if you are driving an inductive load you need to
double the current needed

Why is this???


Is a solenoid an inductive load????

 

[Styx]

Hi All,

IS it true that if you are driving an inductive load you need to
double the current needed

Why is this???


Is a solenoid an inductive load????

no??? where did you here that???

And yes a solenoid is an inductor - it is just the MMF is put to some use

 

[Asjad]

clamping diode

What rating should be the clamping diode
across the coil.

Double the rate voltage of coil??

 

[Russlk]

Double the voltage is good design. You also need to consider the current altho the rating of the diode does not have to exceed the inductor current because it is only conducting a short time.

 

[Styx]

however you do get reverse-recovery current. This is extremly bad in Schoky diode (greater than 2x the inductor current).

An IGBT module I am working on at the moment has a reverse-recovery current of 200A on a 600A switching


This excess current is from teh finite time between switching a switch off to the free-wheel doide turning on. During this time the inductor is seen to be open-circuit with current still wanting to flow so volts rise across the inductor. Once the diode starts to conduct it must cope with more current that was originally switched into the coil.

So from your first question the inductor could see more current than the design intended, but you dont have to provide it with more.

Try and get equally timed switching BJT/FET/IGBT and diode since if the the diode is too fast the switch will then have the reverse-recovery problem