BJT or MOSFET

[Deleted]

Dear all, we have in our lab an inductive load that has an internal esistance of about 25 Ohm, it is required to
varying the DC current through that coil from 0.5A to 5.5A to perform its operation, and so i think in PWM that switch
this inductive load ON and OFF from a 150 VDC supply and by varying the DUTY CYCLE of the PWM circuit, we can then adjust
the average DC current... Now is this right or not, and if this is right what is better to switch this load BJT or MOSFET
. by the way, the inductance of this load is neglectible..

I read about the TIPL755 and in its datasheet listed that it is for fast inductive load switching. is it better or using
power MOS such as BUZ45..

( i forgot in this schematic the free wheeling diode, but it is already placed )..

am waiting for your helpful replies, thanx in advance......... M.Shendy
img512.imageshack.us/img512/3953/comparizonvh1.th.png "] ** img512.imageshack.us/my.php?image=comparizonvh1.png]img512.imageshack.us/img512/3953/comparizonvh1.th.png

[Deleted]

is my question so difficult? why no one replies till now, i just need guidance not total solution... thanx

[Gary Lecomte]

Most of the persons on this forum are amateurs and won't have any comments on your problem.
And I only come to this forum about once a week.

Since I haven't used the TIPL755 for any application, I can't comment on it being better or worse. Nor do I have the BUZ45.

And how can you say: "the Inductance of this load is neglectable".
Any time there is a frequency with an inductive load, there are possible complications.
DEFINATELY FREQUENCY IS A CONSIDERATION!

Yes, PWM will control the Average Current.
And from your description of what you want to do, ANY Mosfet with a suitable voltage rating should work fine.

If I were doing this, I would probably use an IRF740, mainly because it meets the voltage and current requirements, and I have these.

And also based on what your telling me about your application, I would use a "CATCH DIODE" With Filtering Capacitor, To Create a STABLE Average Output Current.

[Deleted]

thanx Gary for your help, and sorry that i was missunderstand..
let me now ask you, the IRF740 has a datasheet says that Id = 10A.. is this really that this ( TO-220) package can carry 10 Amp!!!. are the lead of this small size can carry such small device.
and what is the CATCH DIODE ? do you mean Free Wheeling Diode ? and the filter cap. is it placed in Parallel with load and what is its value?

i promise you that will be the last question... thanx very much........ Shendy

[Gary Lecomte]

Here is a Typical Circuit.

www3.telus.net/chemelec/Temp/Catch-Diode-2.png

Yes the IRF740 will handle the 10 Amps, Continuous.
ASSUMING you use a SUITABLE HEAT SINK.

Even Much More Current, if its a short Pulse Width on the Duty Cycle.

And you can Ask All the Questions you want.
I really don't care.

[Deleted]

thanx a lot Gary Lecomte for your help..