h-bridge circuit question (newbie)
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I'd like to build an h-bridge out of discrete components to control a
bipolar stepper motor with a BS1. I found a schematic on the net
that meets my specs at:
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
I realize that I will need two of these to control the stepper, and
that is fine. I understand the purpose of the h-bridge, but I can't
seem to make sense of *why* this particular circuit works. I think
I'm getting tangled up with the PNP TIP's and the fact that the
collectors are common.
If anyone has time to take a look and maybe point me in the right
direction to better understand, I would appreciate it. I've already
read virtually every web tutorial on transistors -- but they're a
little lite on PNP's.
Thanks in advance.
Rob
bipolar stepper motor with a BS1. I found a schematic on the net
that meets my specs at:
http://www.bobblick.com/techref/projects/hbridge/hbridge.html
I realize that I will need two of these to control the stepper, and
that is fine. I understand the purpose of the h-bridge, but I can't
seem to make sense of *why* this particular circuit works. I think
I'm getting tangled up with the PNP TIP's and the fact that the
collectors are common.
If anyone has time to take a look and maybe point me in the right
direction to better understand, I would appreciate it. I've already
read virtually every web tutorial on transistors -- but they're a
little lite on PNP's.
Thanks in advance.
Rob
Comments
rrothe@m... writes:
> I'd like to build an h-bridge out of discrete components to control a
> bipolar stepper motor with a BS1. I found a schematic on the net
> that meets my specs at:
>
> http://www.bobblick.com/techref/projects/hbridge/hbridge.html
>
> I realize that I will need two of these to control the stepper, and
> that is fine. I understand the purpose of the h-bridge, but I can't
> seem to make sense of *why* this particular circuit works. I think
> I'm getting tangled up with the PNP TIP's and the fact that the
> collectors are common.
>
> If anyone has time to take a look and maybe point me in the right
> direction to better understand, I would appreciate it. I've already
> read virtually every web tutorial on transistors -- but they're a
> little lite on PNP's.
>
> Thanks in advance.
>
> Rob
>
>
>
>
Rob,
When the circuit works properly, only two transistors are on at one time. The
two on will be Q1 & Q4, or Q2 & Q3.
The PNP's will supply + voltage, and the NPN's supply a ground path.
When one pair is on (Q1 Q4),the motor will spin one direction due to the + -
polarity. When the other pair of transistors is on (Q2 Q3) the polarity of the
motor is reversed, making it spin the opposite direction.......
If I did not explain well enough, give me a phone number and a good time to
call.
Ken
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rrothe@m... writes:
>
> I'd like to build an h-bridge out of discrete components to control a
> bipolar stepper motor with a BS1. I found a schematic on the net
> that meets my specs at:
>
> http://www.bobblick.com/techref/projects/hbridge/hbridge.html
>
> I realize that I will need two of these to control the stepper, and
> that is fine. I understand the purpose of the h-bridge, but I can't
> seem to make sense of *why* this particular circuit works. I think
> I'm getting tangled up with the PNP TIP's and the fact that the
> collectors are common.
>
> If anyone has time to take a look and maybe point me in the right
> direction to better understand, I would appreciate it. I've already
> read virtually every web tutorial on transistors -- but they're a
> little lite on PNP's.
>
> Thanks in advance.
>
> Rob
>
>
Also. ,motor A & motor B designates the terminals on the SAME
motor.......terminal A and termial B.....
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was kind enough to send me the following...
> Hi Jack,
>
> The darlington power transistors Q1,2,3 and 4 have internal pinch-off
> resistors, so they turn off and stay off naturally. They also have
> internal
> diodes emitter-collector, that act as freewheel diodes in this
> circuit. It
> simplifies things, because those parts would have to be added if
> regular
> transistors were used.
>
> To make the motor go in one direction, turning on Q1 and Q4 will put
> positive to motor A and negative to motor B. Transistor Q5 does this,
> so if
> you apply a logic-level(5 volts or less) to control a, that's what
> happens.
> If you activate control b, Q6 turns on Q2 and Q3 and the motor runs
> in the
> other direction. The lower transistors Q7 and Q8 prevent short
> circuits
> from occurring if both control a and b are activated simultaneously,
> by
> removing the drive from Q3 and Q4. The side benefit from this is that
> if
> both control a and b are activated, the top darlingtons Q1 and Q2 are
> on,
> and short the motor, effectively slowing the motor(electrical
> braking).
>
> Hope that answers your questions!
>
> Cheerful regards,
> Bob
>
> At 03:21 PM 7/2/98 -0700, you wrote:
> >Hi Bob
> >
> >Wonder if you have time for a brief explanation of how your
> >H-bridge circuit works?
> >Certainly understand if you're too busy - I may have to
> >build it to figure it out otherwise, although I try to do
> >it the other way round.
> >I enjoy your stuff. Thanks.
> >