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hfe

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danielsmusic

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what is the the unit "HFE" is it the sencitivity at the bass of a transistor
 
The term hFE is a transistor's DC current gain at a certain collector current and voltage and temperature.
The term hfe is a transistor's AC current gain.

The current gains vary betwween transistors having the same part number by up to 9 times. The current gains change with a change of collector current and voltage and the temperature.

Yes, you could say that a transistor's current gain is its sensitivity at its base.
 
Ah yes, thank you for pointing out my mistake. I didn't make the distinction for 2 reasons. 1. I didn't know there was a difference between HFE and hfe :) and 2. I call the DC gain (as do my books) beta.

Thanks!
 
i was only asking because i need a switching biplar transistor for a stepper motor driver. just run from a 4017 chip.
 
danielsmusic said:
i was only asking because i need a switching biplar transistor for a stepper motor driver. just run from a 4017 chip.

It depends on a number of things, for a start you should feed the base of the transistors through current limiting resistors from the 4017. I would suggest checking the maximum output current for the 4017, and calculating the resistors to give as much base current as possible (because transistors have seriously less gain at low collector voltages, and you're wanting to run them saturated).

Obviously the next thing is how much current the motor requires?, you need to pick a transistor that has enough current handling, dissipation, and enough current gain to switch fully with the output from the 4017.

But as with other people, I'm slightly confused by the choice of a 4017?, it doesn't appear to be very suitable?.
 
Nigel Goodwin said:
But as with other people, I'm slightly confused by the choice of a 4017?, it doesn't appear to be very suitable?.

Indeed, 4017 would hardly give enough current to drive bjts to saturation if the collector current is high. U should try mosfets or use a current buffer between the IC & the transistors.
 
With a 9V supply, a CD4017B will give about 10mA directly into a transistor's base without a current-limiting resistor. The IC's Cmos transistor will dissipate only 80mW. The current and dissipation are higher with a higher supply voltage when you would need to use a resistor.

A TIP31 transistor saturates well with a base current of 50mA or more when it has a load of only 1A so the 4017 definately needs a buffer transistor to drive it. :lol:
 
well im sorry to say your all wrong :lol: (no disrespect though)
i built it and it worked fine with a tip41c no resistors. 12v 1A on collecter
output through diodes to transistor to drive the motor. i know it was not the best way to do it but it worked for what i want.
 
Sure it will work if you were lucky and got a transistor with 10 times more gain than guaranteed minimum. Don't make a thousand circuits like that because many of them won't work.
 
danielsmusic said:
i used switching transistors (very high gain)

I thought you previously said you had used TIP41's?.

These are general purpose power transistors, NOT switching transistors, and certainly don't have very high gain.
 
i have used tip41's it does power the motor but the sequence it wrong it just goes back and forward
 
sorry,
but when i connected each wire to a switch and did the same sequence as the 4017 it worked fine, a little slow.
so i just thought it mite work with a 4017.
does anybody have any suggestions.
 
danielsmusic said:
sorry,
but when i connected each wire to a switch and did the same sequence as the 4017 it worked fine, a little slow.
so i just thought it mite work with a 4017.
does anybody have any suggestions.

Google for "stepper motor tutorial", LOAD'S of information for you!.
 
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