Is a computer fan an inductive load?

Howdy,

I am designing a circuit to switch on and off a computer fan with an NPN
transistor. I am wondering if I should use a diode across the computer fan,
to protect the transistor agains trainsients from switching (if the fan
behaves as an inductive load).

Thanks for any advice on this,

Jon

Jon Danniken wrote:
> Howdy,
>
> I am designing a circuit to switch on and off a computer fan with an NPN
> transistor. I am wondering if I should use a diode across the computer fan,
> to protect the transistor agains trainsients from switching (if the fan
> behaves as an inductive load).
>
> Thanks for any advice on this,

Even if the fan contains a brushless commutation circuit. it
probably exhibits some inductive behavior at the supply
terminals. I would add the diode.

John Popelish wrote:
> Jon Danniken wrote:
>> Howdy,
>>
>> I am designing a circuit to switch on and off a computer fan with an NPN
>> transistor. I am wondering if I should use a diode across the
>> computer fan,
>> to protect the transistor agains trainsients from switching (if the fan
>> behaves as an inductive load).
>>
>> Thanks for any advice on this,
>
> Even if the fan contains a brushless commutation circuit. it probably
> exhibits some inductive behavior at the supply terminals. I would add
> the diode.

Sorry, but on thinking about this a bit more, any brushless
driver will probably act as a diode across the motor, when
power is disconnected.

On Mon, 20 Nov 2006 16:49:45 -0800, "Jon Danniken"
<(E-Mail Removed)> wrote:

>Howdy,
>
>I am designing a circuit to switch on and off a computer fan with an NPN
>transistor. I am wondering if I should use a diode across the computer fan,
>to protect the transistor agains trainsients from switching (if the fan
>behaves as an inductive load).

Try watching the voltage on a CRO as you switch it off (with a switch) - if
there is an inductive kick it should be visible.

or use a diode anyway, to be sure to be sure. They're cheap.

"John Popelish" wrote;
> John Popelish wrote:
> > Jon Danniken wrote:
> >> Howdy,
> >>
> >> I am designing a circuit to switch on and off a computer fan with an
NPN
> >> transistor. I am wondering if I should use a diode across the
> >> computer fan,
> >> to protect the transistor agains trainsients from switching (if the fan
> >> behaves as an inductive load).
> >>
> >> Thanks for any advice on this,
> >
> > Even if the fan contains a brushless commutation circuit. it probably
> > exhibits some inductive behavior at the supply terminals. I would add
> > the diode.
>
> Sorry, but on thinking about this a bit more, any brushless
> driver will probably act as a diode across the motor, when
> power is disconnected.

Thanks, John, and Rebel. I'll probably just add the diode just to on the
safe side.

Thanks,

Jon