H-Bridge Isolating
Archiver
Posts: 46,084
I'm making an H-bridge out of mosfets for one of my projects I was
wondering if a 7407 buffer is sufficient to isolate the circuit from
damaging my stamp or should I go full out and use opto-Isolation any
experience or theores on this would be greatly appreciated
Thank You
wondering if a 7407 buffer is sufficient to isolate the circuit from
damaging my stamp or should I go full out and use opto-Isolation any
experience or theores on this would be greatly appreciated
Thank You
Comments
On my sumo robot, the motors ran at 24v, and took about 1 amp stall..
I've fried a basic stamp tottaly, and damaged some pins on another
when my l298 burnt out (the motors where really nasty, so it was the
power spikes (emf) that did 'em in).. I didn't have any isolation.
for apps with smaller power motors (I'd say less than 9 volts, less
than 250mA stall sort of thing) you could probably get away only with
a buffer, or even nothing (provided your motor driver
doesn't 'release trapped smoke' (aka burn out))
One good thing to remember for controlling motors, is that it is
better safe than sorry. Build in spike protection, have your drivers
rated for higher voltage and amperage than your motors will take..
Hope that helps..
~Roger~
TenFour
--- In basicstamps@y..., wooticity@y... wrote:
> I'm making an H-bridge out of mosfets for one of my projects I was
> wondering if a 7407 buffer is sufficient to isolate the circuit
from
> damaging my stamp or should I go full out and use opto-Isolation
any
> experience or theores on this would be greatly appreciated
>
> Thank You
stamp and the bridge that absolutely, positively, prevents the upper
and lower transistors from turning on at the same time.
Using MOSFETS is a much better way to go than bipolar, much lower on
resistance. By using MOSFETS in your H bridge the transistors will
not run hot, and more power will make it to the load.
Turning on the low side driver is not a problem. Turning on the high
side driver is a bit nmore difficult. The MOSFET gate requires a
higher voltage than the voltage you switch. The answer here is a
MOSFET H-bridge driver IC. It has all the logic in it to prevent
damage to the bridge. Also on the chip: charge pumps to properly turn
on the high-side drivers. I would not do this without MOSFETS and the
MOSFET H-bridge driver IC. There are H-bridge driver chips that have
serial inputs. These easily interface to your stamp.
Regards
Rich
AA2DN
--- In basicstamps@y..., wooticity@y... wrote:
> I'm making an H-bridge out of mosfets for one of my projects I was
> wondering if a 7407 buffer is sufficient to isolate the circuit
from
> damaging my stamp or should I go full out and use opto-Isolation
any
> experience or theores on this would be greatly appreciated
>
> Thank You
side?
If you use P-channel mosfets for the top side*, you don't need a
higher switching voltage (it'll act like a regular pnp/npn h-bridge,
and the overall design is easier)), although a driver that turns the
gate on quickly (to prevent it passing through linear mode for too
long) is a good idea.. I use the TC4427, which is a nice dual mosfet
driver IC. All you do is put the driver between the mosfet's gate and
logic signal. To prevent the high and low side mosfets from turning
on at the same time, I just connect the gates of the higher and lower
mosfets on a half bridge togethor (or rather the inputs for the
drivers that connect to the gates) togethor, since one will turn on
with a logic low, and the other with a logic high. But this is not
the ideal set up if you're using PWM...
* P-channel mosfets are indeed harder to find, and more expensive,
but they're not that bad. I got mine from digikey, as they have a
wide selection. I use the IRF9540 and the IRF540 togethor..
~Roger~
TenFour
--- In basicstamps@y..., iceninevt@y... wrote:
> It is also very important that there be a bit of logic between the
> stamp and the bridge that absolutely, positively, prevents the
upper
> and lower transistors from turning on at the same time.
>
> Using MOSFETS is a much better way to go than bipolar, much lower
on
> resistance. By using MOSFETS in your H bridge the transistors will
> not run hot, and more power will make it to the load.
>
> Turning on the low side driver is not a problem. Turning on the
high
> side driver is a bit nmore difficult. The MOSFET gate requires a
> higher voltage than the voltage you switch. The answer here is a
> MOSFET H-bridge driver IC. It has all the logic in it to prevent
> damage to the bridge. Also on the chip: charge pumps to properly
turn
> on the high-side drivers. I would not do this without MOSFETS and
the
> MOSFET H-bridge driver IC. There are H-bridge driver chips that
have
> serial inputs. These easily interface to your stamp.
>
> Regards
>
> Rich
> AA2DN
>
>
>
> --- In basicstamps@y..., wooticity@y... wrote:
> > I'm making an H-bridge out of mosfets for one of my projects I
was
> > wondering if a 7407 buffer is sufficient to isolate the circuit
> from
> > damaging my stamp or should I go full out and use opto-Isolation
> any
> > experience or theores on this would be greatly appreciated
> >
> > Thank You
inputs into it on the output of it or is an opto-isolator no longer
neccesary?
Thank you for all of your help
--- In basicstamps@y..., "Roger K" <korus@i...> wrote:
> Are you refering to Mosfet bridges that use N-channels for the high
> side?
>
> If you use P-channel mosfets for the top side*, you don't need a
> higher switching voltage (it'll act like a regular pnp/npn h-
bridge,
> and the overall design is easier)), although a driver that turns
the
> gate on quickly (to prevent it passing through linear mode for too
> long) is a good idea.. I use the TC4427, which is a nice dual
mosfet
> driver IC. All you do is put the driver between the mosfet's gate
and
> logic signal. To prevent the high and low side mosfets from turning
> on at the same time, I just connect the gates of the higher and
lower
> mosfets on a half bridge togethor (or rather the inputs for the
> drivers that connect to the gates) togethor, since one will turn on
> with a logic low, and the other with a logic high. But this is not
> the ideal set up if you're using PWM...
>
> * P-channel mosfets are indeed harder to find, and more expensive,
> but they're not that bad. I got mine from digikey, as they have a
> wide selection. I use the IRF9540 and the IRF540 togethor..
>
>
> ~Roger~
> TenFour
>
>
> --- In basicstamps@y..., iceninevt@y... wrote:
> > It is also very important that there be a bit of logic between
the
> > stamp and the bridge that absolutely, positively, prevents the
> upper
> > and lower transistors from turning on at the same time.
> >
> > Using MOSFETS is a much better way to go than bipolar, much lower
> on
> > resistance. By using MOSFETS in your H bridge the transistors
will
> > not run hot, and more power will make it to the load.
> >
> > Turning on the low side driver is not a problem. Turning on the
> high
> > side driver is a bit nmore difficult. The MOSFET gate requires a
> > higher voltage than the voltage you switch. The answer here is a
> > MOSFET H-bridge driver IC. It has all the logic in it to prevent
> > damage to the bridge. Also on the chip: charge pumps to properly
> turn
> > on the high-side drivers. I would not do this without MOSFETS and
> the
> > MOSFET H-bridge driver IC. There are H-bridge driver chips that
> have
> > serial inputs. These easily interface to your stamp.
> >
> > Regards
> >
> > Rich
> > AA2DN
> >
> >
> >
> > --- In basicstamps@y..., wooticity@y... wrote:
> > > I'm making an H-bridge out of mosfets for one of my projects I
> was
> > > wondering if a 7407 buffer is sufficient to isolate the circuit
> > from
> > > damaging my stamp or should I go full out and use opto-
Isolation
> > any
> > > experience or theores on this would be greatly appreciated
> > >
> > > Thank You
out to test it [noparse]:)[/noparse] I use mosfets rated at 100v and 19 amps, but my
motors are running at 7.2 volts and about 4 amps stall (which is
incredibly hard to do), so I've got a good safety zone. I guess if
you do the same and get mosfets rated for much higher than your
motors will take, your bridge shouldn't burn out, so the opto-
isolation would not be neccesary.
The TC4427 is a buffer/driver, so you could probably get away with
just using that... I suggest checking out the datasheet.. It has some
usefull information on it (like how much reverse current it can take,
spike voltages, etc.)
http://www.telcom-semi.com/products/datasheets/tc4426_8.pdf
~Roger~
TenFour
--- In basicstamps@y..., wooticity@y... wrote:
> So if I use tc4427 should I still use an opto-Isolator for the
> inputs into it on the output of it or is an opto-isolator no longer
> neccesary?
>
> Thank you for all of your help
>
>
> --- In basicstamps@y..., "Roger K" <korus@i...> wrote:
> > Are you refering to Mosfet bridges that use N-channels for the
high
> > side?
> >
> > If you use P-channel mosfets for the top side*, you don't need a
> > higher switching voltage (it'll act like a regular pnp/npn h-
> bridge,
> > and the overall design is easier)), although a driver that turns
> the
> > gate on quickly (to prevent it passing through linear mode for
too
> > long) is a good idea.. I use the TC4427, which is a nice dual
> mosfet
> > driver IC. All you do is put the driver between the mosfet's gate
> and
> > logic signal. To prevent the high and low side mosfets from
turning
> > on at the same time, I just connect the gates of the higher and
> lower
> > mosfets on a half bridge togethor (or rather the inputs for the
> > drivers that connect to the gates) togethor, since one will turn
on
> > with a logic low, and the other with a logic high. But this is
not
> > the ideal set up if you're using PWM...
> >
> > * P-channel mosfets are indeed harder to find, and more
expensive,
> > but they're not that bad. I got mine from digikey, as they have a
> > wide selection. I use the IRF9540 and the IRF540 togethor..
> >
> >
> > ~Roger~
> > TenFour
> >
> >
> > --- In basicstamps@y..., iceninevt@y... wrote:
> > > It is also very important that there be a bit of logic between
> the
> > > stamp and the bridge that absolutely, positively, prevents the
> > upper
> > > and lower transistors from turning on at the same time.
> > >
> > > Using MOSFETS is a much better way to go than bipolar, much
lower
> > on
> > > resistance. By using MOSFETS in your H bridge the transistors
> will
> > > not run hot, and more power will make it to the load.
> > >
> > > Turning on the low side driver is not a problem. Turning on
the
> > high
> > > side driver is a bit nmore difficult. The MOSFET gate requires
a
> > > higher voltage than the voltage you switch. The answer here is
a
> > > MOSFET H-bridge driver IC. It has all the logic in it to
prevent
> > > damage to the bridge. Also on the chip: charge pumps to
properly
> > turn
> > > on the high-side drivers. I would not do this without MOSFETS
and
> > the
> > > MOSFET H-bridge driver IC. There are H-bridge driver chips that
> > have
> > > serial inputs. These easily interface to your stamp.
> > >
> > > Regards
> > >
> > > Rich
> > > AA2DN
> > >
> > >
> > >
> > > --- In basicstamps@y..., wooticity@y... wrote:
> > > > I'm making an H-bridge out of mosfets for one of my projects
I
> > was
> > > > wondering if a 7407 buffer is sufficient to isolate the
circuit
> > > from
> > > > damaging my stamp or should I go full out and use opto-
> Isolation
> > > any
> > > > experience or theores on this would be greatly appreciated
> > > >
> > > > Thank You
- 50 volts DC at about 2 amps. Thanks
those ratings.
http://www.allegromicro.com/selguide/motors1.htm
Original Message
> Can you suggest a good H bridge driver as you suggest. I need to switch +
and
> - 50 volts DC at about 2 amps. Thanks