Author Topic: Use 2N4401 transistor to drive 59mA stepper motor  (Read 767 times)

0 Members and 1 Guest are viewing this topic.

Offline circuit12Topic starter

  • Newbie
  • !
  • Posts: 1
  • Country: cn
Use 2N4401 transistor to drive 59mA stepper motor
« on: July 21, 2018, 02:35:37 am »
A while ago I asked a question about driving a stepper motor using a 2N5550 and was advised that it wasn't really capable/a good idea. I received a good answer but would like a bit more information really so that I can make these decisions for myself in the future.

2N5550
On the 2N5550 transistors PDF it says it can drive up to 600mA (DC) under the maximum ratings (am I interpreting this correctly?):

Ic Max rating

If this is correct, why does the DC Current gain graph only show up to 100mA, is this just because it can handle 600mA but would be almost pointless to actually use it for that because of the low gain at that level?

hFE

2N4401
So this brings me to the 2N4401. The 2N4401 application also says the max collector current can be 600mA (again, am I interpreting this correctly?).



Now the current gain graph on this transistor shows it going up to 300mA however it says "pulsed" in the title of the graph and there doesn't seem to be a graph for continuous so I'm a little confused why this might be? I suppose driving a stepper motor would come under the category of pulsed though?



So assuming that this is suitable for driving my 259mA stepper motor I would need to supply the base with about (259/150) 1.7mA (259 being the number of mA needed by the stepper motor and 150 being roughly the current gain (derived from the graph)?), is this correct?

I understand that from my other question I should really use a MOSFET as they are better suited to the job, I just have a handful of these 2N4401s kicking about that I thought I could test my code and theory with.

Thanks in advance and I'd appreciate a response to even the little questions I raised like the "am I interpreting this correctly?" ones, just to reassure me that I'm on the right lines (or not).
 

Online Zero999

  • Super Contributor
  • ***
  • Posts: 19345
  • Country: gb
  • 0999
Re: Use 2N4401 transistor to drive 59mA stepper motor
« Reply #1 on: July 21, 2018, 08:54:28 am »
Just a few points:

The entire operating area of a transistor is seldom given on the data sheet.

It's bad practise to run a component, continuously at its maximum ratings.

The higher current gains are only specified with a relatively high VCE of 2V or 5V, which will be far too higher voltage drop for your application.

1.7mA of base drive will be nowhere near enough for a collector current of 259mA. To saturate a BJT s ratio of 1:10 between the base and collector current is normally recommended, but it can be lower or high, depending on the part and application. Quickly looking at the data sheet for the 2N4401, you could probably get away with a base current of 1/20 of the collector current, which would be 13mA.

http://www.farnell.com/datasheets/661741.pdf
 

Offline David Hess

  • Super Contributor
  • ***
  • Posts: 16548
  • Country: us
  • DavidH
Re: Use 2N4401 transistor to drive 59mA stepper motor
« Reply #2 on: July 21, 2018, 12:15:11 pm »
A while ago I asked a question about driving a stepper motor using a 2N5550 and was advised that it wasn't really capable/a good idea. I received a good answer but would like a bit more information really so that I can make these decisions for myself in the future.

The 2N5550 is intended for higher voltage applications.

Quote
On the 2N5550 transistors PDF it says it can drive up to 600mA (DC) under the maximum ratings (am I interpreting this correctly?):

That is right.

Quote
If this is correct, why does the DC Current gain graph only show up to 100mA, is this just because it can handle 600mA but would be almost pointless to actually use it for that because of the low gain at that level?

That basically sums it up.  Datasheets usually only include specifications suitable for the intended applications.  For instance the 2N5550 datasheet specifies current gain from 1 to 50 milliamps while the 2N4401 datasheet specifies current gain from 0.1 to 500 milliamps.

Quote
So this brings me to the 2N4401. The 2N4401 application also says the max collector current can be 600mA (again, am I interpreting this correctly?).

Yes, and it even has specifications for operation at 500 milliamps.

Quote
Now the current gain graph on this transistor shows it going up to 300mA however it says "pulsed" in the title of the graph and there doesn't seem to be a graph for continuous so I'm a little confused why this might be? I suppose driving a stepper motor would come under the category of pulsed though?

You will need to provide a link because my 2N4401 datasheet does not have that.

Pulsed usually means that the transistor is operating at high power dissipation so the test has to be short.

Quote
So assuming that this is suitable for driving my 259mA stepper motor I would need to supply the base with about (259/150) 1.7mA (259 being the number of mA needed by the stepper motor and 150 being roughly the current gain (derived from the graph)?), is this correct?

More like 13 milliamps like Hero999 says.  Current gain falls at high collector currents.

Quote
I understand that from my other question I should really use a MOSFET as they are better suited to the job, I just have a handful of these 2N4401s kicking about that I thought I could test my code and theory with.

There is nothing wrong with using the 2N4401 in this application.
 


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf