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Topic: How to use TIP41C's as a substitute for this example? (Read 10161 times) previous topic - next topic

TECH GEEK

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MarkT

bases via a resistor to the relevant Arduino pin, collectors to the stepper winding, emitter to ground.  Also freewheel diode across each winding.

The problem is they are low gain so may not be enough - how much current do you need per winding?  You can only source about 30mA from an Arduino pin safely and with a gain of about 20 that only gives 0.6A from the TIP41C.  Since the ULN2004 can do 0.5A and has freewheel diodes integrated the TIP41C can only add a bit more thermal ruggedness unless you have more transistors to drive them.

I think you'd be better off with ZTX851's which have gain of 100 - can switch 3A given 30mA of drive.
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TECH GEEK

i'm not sure but this is the brand of stepper i have = applied motion products, inc
Model # = HT17-075
DC4V      1.2A/(Holding Toque)      3.3ohms   200S/R
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focalist

#3
May 18, 2011, 02:52 am Last Edit: May 18, 2011, 02:55 am by focalist Reason: 1
Seems to be a popular thing to be doing.  I'm using 3904's myself, but will need to replace them with something with higher current capacity when I eventually cook them by using too large a stepper.  They can only handle 200ma or so, but have a gain well over 100 at 10ma to the base.

Take a read through:
http://arduino.cc/forum/index.php/topic,60571.0.html

Picking the specific transistor is mainly a function of gain (as noted above) and current capacity, it seems.. but the circuit I'm using seems to work well at the moment.

TECH GEEK

can someone please tell me if TIP41C's will work with this 8-wire stepper or would TIP120's be better? or any other recommendations for this stepper of which i can't afford any others?

   also i'm making a laser-pointer-pointer (yes 2*pointer).
I plan on using the stepper motor model above (or if possible a cd-drive stepper)
to point an astronomy-grade laser-pointer at a location in the sky (at night)
so I can find stuff with my professional-grade telescope.(By this I mean pointing my laser at the LOCATION in the sky. <<<THIS DOES NOT NECESSARILY MEAN WHILE OUTSIDE!!!!) (All caps so you will read this fully, and not say "That is dangerous to planes, birds, etc. etc.!!!" )
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TECH GEEK

nevermind mis-read & misunderstood the comments...
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MarkT

1.2A is too much for a TIP41C driven direct from Arduino pin - just doesn't have the current gain.  Adding a 2n2222 in Darlington config will get you the gain though.

Its generally the case that power transistors have poor current gain - I've often wondered why...  There are some much better switching transistors about these days like the ZTX851 I mentioned earlier - high gain, very very low Vsat, high speed.  Why stick with 1970's tech?
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TECH GEEK


1.2A is too much for a TIP41C driven direct from Arduino pin - just doesn't have the current gain.  Adding a 2n2222 in Darlington config will get you the gain though.


What about Tip120g's? (Mine have ~650 hFE)


Why stick with 1970's tech?


it all i can find from trash picking & all I can afford...

ps i've got the flu so my replies will be at time very delayed
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TECH GEEK

also if anyone knows of a way to get electronics for very cheap let me know...
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TECH GEEK

i also noticed the stepper's voltage max is 4V,m which wold mean the power supply would need to be 4V...

is this a problem if i use tip120g's and an Arduino mega wich runs of 5V logic?
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TECH GEEK

As always... Thanks for posting!!!

MarkT

5V will make the motor run a bit hotter - but there will be about 1V lost in the TIP120 anyway since its a darlington so that won't be an issue.

Make sure your supply is up to the current - best not to share with the Arduino, definitely don't use the on-board regulator to generate you motor supply - use a separate 5V regulator is best
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TECH GEEK

As always... Thanks for posting!!!

TECH GEEK

#13
May 19, 2011, 07:21 pm Last Edit: May 19, 2011, 08:14 pm by TECH GEEK Reason: 1
also the supply is DC 5V 5A
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