I have a motor control circuit (H-Bridge) and its powered off 6 volts.
I am using a pic to control the motors, and my problem is that since I
am only supplying 5 volts and the control, the motors don't go their
full speed. How can I fix this. I realize this is not a programming
question but it still involves a PIC and I couldn't find anyone else to
ask...:)
Thanks a lot, I know you guys will come through for me.
> Date: Fri, 29 Nov 1996 20:41:31 -0800
> From: spam_OUTdeicideTakeThisOuTPSNW.COM
> I have a motor control circuit (H-Bridge) and its powered off 6 volts.
> I am using a pic to control the motors, and my problem is that since I
> am only supplying 5 volts and the control, the motors don't go their
> full speed. How can I fix this.
Depends on what the H bridge is made from.
If NPN on bottom and PNP on top you need a better interface to the
PNP's to get them full on. Probably some sort of drive transistor.
You might be able to get by with a diode in series with
the base of the PNPs as you only have 6 volt supply.
IF N channel MOSFET on bottom and top, then make sure the bottom ones
are logic (5V) gate. Top parts will need a charge pump driver
circuit to get the gate higher than 6V + gate turn on voltage.
If P chan MOSFET on top, then you need a driver to get logic output
translated to +6V and ground, and you need a logic gate device.
Supply more info and maybe we can help more.
Gary Skinner .....gskinnerKILLspam@spam@csd.net
Electronic Solutions, Inc.
design of custom electronic controls
>
> > Date: Fri, 29 Nov 1996 20:41:31 -0800
> > From: deicideKILLspamPSNW.COM
> > I have a motor control circuit (H-Bridge) and its powered off 6 volts.
> > I am using a pic to control the motors, and my problem is that since I
> > am only supplying 5 volts and the control, the motors don't go their
> > full speed. How can I fix this.
>
> Depends on what the H bridge is made from.
> If NPN on bottom and PNP on top you need a better interface to the
> PNP's to get them full on. Probably some sort of drive transistor.
> You might be able to get by with a diode in series with
> the base of the PNPs as you only have 6 volt supply.
>
> IF N channel MOSFET on bottom and top, then make sure the bottom ones
> are logic (5V) gate. Top parts will need a charge pump driver
> circuit to get the gate higher than 6V + gate turn on voltage.
>
> If P chan MOSFET on top, then you need a driver to get logic output
> translated to +6V and ground, and you need a logic gate device.
>
> Supply more info and maybe we can help more.
> Gary Skinner .....gskinnerKILLspam.....csd.net
> Electronic Solutions, Inc.
> design of custom electronic controls
its made of TIP120 and TIP125 transistors....4 for one motor and 4 for
the other....4 125 and 4 120's but not mixed....don't ask me why i did
it this way...:)
snip
> its made of TIP120 and TIP125 transistors....4 for one motor and 4 for
> the other....4 125 and 4 120's but not mixed....don't ask me why i did
> it this way...:)
Use two output pins on the pic,
drive the low side transistors(NPN's)direct via 500 Ohms
also use these pins to drive via 4k7 two NPN (bc337) emitter
grounded the 337's are use to drive the bases on the opposite
side of your high side drivers (PNP's)
ONE PIN MUST DRIVE THE LOW SIDE AND THE OPPOSITE HIGH SIDE
NOT THE SAME SIDE
use 500 0hms from the colector 337 to base of highside and
2k7 from highside base to emitter
After Bill Gates announced to the world that he was Microsoft,
his wife was asked to comment. She said that as his wife, she
had been the first to notice this problem
If you don't need to control the speed of the DC motors, just be able to
make them run to one side or the other, I have used the following circuit,
which uses 2 NPN and 2 PNP, 2 pins of the pic, and you can power the motor
with a different source than the pic (ie pic with 5V and motors with 8V).
Be sure to NEVER place a "1" on both inputs at the same time! Both inputs
in "0" will cause the motor to stop. A "1" on one input will make the motor
turn to one side, and a "1" on the other will make it turn to the other
side. The circuit will "loose" aprox. .6V (.3 in each transistor), so if
you need to power the motors with exactly 6v, you will need a 6.6V power
supply. Here comes the circuit (one of the motor wires is "A" and the other
is "B"):
8V 0------------------------
| |
/ \
____/\/\/\__|< >|____/\/\/\__
| |\ /| |
| \ / |
| |__ __| |
| A B |
| |
| |
| |
| |
| B A |
--------------|-- --|---------------
| |
/ \
__/\/\/\__|/ \|____/\/\/\__
|\ /|
to pic > < to pic
| |
| |
_ _
- -
At 08:41 PM 11/29/96 -0800, you wrote:
>I have a motor control circuit (H-Bridge) and its powered off 6 volts.
>I am using a pic to control the motors, and my problem is that since I
>am only supplying 5 volts and the control, the motors don't go their
>full speed. How can I fix this. I realize this is not a programming
>question but it still involves a PIC and I couldn't find anyone else to
>ask...:)
>
>Thanks a lot, I know you guys will come through for me.
>
>
____________________
Gonzalo Palarea chalospam_OUTinfovia.com.gt
>
> If you don't need to control the speed of the DC motors, just be able to
> make them run to one side or the other, I have used the following circuit,
> which uses 2 NPN and 2 PNP, 2 pins of the pic, and you can power the motor
> with a different source than the pic (ie pic with 5V and motors with 8V).
> Be sure to NEVER place a "1" on both inputs at the same time! Both inputs
> in "0" will cause the motor to stop. A "1" on one input will make the motor
> turn to one side, and a "1" on the other will make it turn to the other
> side. The circuit will "loose" aprox. .6V (.3 in each transistor), so if
> you need to power the motors with exactly 6v, you will need a 6.6V power
> supply. Here comes the circuit (one of the motor wires is "A" and the other
> is "B"):
>
> 8V 0------------------------
> | |
> / \
> ____/\/\/\__|< >|____/\/\/\__
> | |\ /| |
> | \ / |
> | |__ __| |
> | A B |
> | |
> | |
> | |
> | |
> | B A |
> --------------|-- --|---------------
> | |
> / \
> __/\/\/\__|/ \|____/\/\/\__
> |\ /|
> to pic > < to pic
> | |
> | |
> _ _
> - -
>
> At 08:41 PM 11/29/96 -0800, you wrote:
> >I have a motor control circuit (H-Bridge) and its powered off 6 volts.
> >I am using a pic to control the motors, and my problem is that since I
> >am only supplying 5 volts and the control, the motors don't go their
> >full speed. How can I fix this. I realize this is not a programming
> >question but it still involves a PIC and I couldn't find anyone else to
> >ask...:)
> >
> >Thanks a lot, I know you guys will come through for me.
> >
> >
> ____________________
> Gonzalo Palarea
> @spam@chaloKILLspaminfovia.com.gt
deicide@PSNW.COM wrote:
>
> I have a motor control circuit (H-Bridge) and its powered off 6 volts.
> I am using a pic to control the motors, and my problem is that since I
> am only supplying 5 volts and the control, the motors don't go their
> full speed. How can I fix this. I realize this is not a programming
> question but it still involves a PIC and I couldn't find anyone else to
> ask...:)
>
> Thanks a lot, I know you guys will come through for me.
if you use the lm293d then you have two pins as logic supply
and driver supply
only the gnd must be shared ( I believe)
deicide@PSNW.COM wrote:
>
> I have a motor control circuit (H-Bridge) and its powered off 6 volts.
> I am using a pic to control the motors, and my problem is that since I
> am only supplying 5 volts and the control, the motors don't go their
> full speed. How can I fix this. I realize this is not a programming
> question but it still involves a PIC and I couldn't find anyone else to
> ask...:)
>
> Thanks a lot, I know you guys will come through for me.
Rip a L293 off an old MFM hard drive. They can handle 1A.
--
Friendly Regards
Tjaart van der Walt
______________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
|+27-(0)11-622-8686 | http://wasp.co.za | KILLspamtjaartKILLspamwasp.co.za |
|______________________________________________________________|
> I have a motor control circuit (H-Bridge) and its powered off 6 volts.
> I am using a pic to control the motors, and my problem is that since I
> am only supplying 5 volts and the control, the motors don't go their
> full speed.
Also realize that you are probably getting even less then 5 V
since you will have a drop acorss your H-Bridge circuit unless it is a relay.
> How can I fix this. I realize this is not a programming
> question but it still involves a PIC and I couldn't find anyone else to
> ask...:)
The solution is to use a higher voltage supply or different motors,
not much else is going to work for a power circuit. You can also rewind
your motors for a lower voltage, it's not as hard as it might sound.
> From: spamBeGonedeicidespamBeGonePSNW.COM
>
> I solved my problem simply.....very simply....:)
>
> I got 2, 5 volt reed switches and controlled them with my pic....then in
> turn they switched the 6 volts...and the pic runs just fine...:)
>
Presumably your motor only draws a couple of hundred milliamps. Reed
switches don't last too long otherwise. Hope you put a snubber
capacitor across the contacts - this will lengthen the life by
suppressing arcing. If you are using transistors in the ground-switching
part of the H-bridge, I guess you could suppress arcing completely
by switching them off before changing the relay state.
Reed relays are pretty pricey - wouldn't it have been cheaper to
use a couple of PNPs in saturation (only 0.3V drop)? Of course,
the relays give you advantage of complete electrical isolation...
> Presumably your motor only draws a couple of hundred milliamps. Reed
> switches don't last too long otherwise.
...
> Reed relays are pretty pricey - wouldn't it have been cheaper to
> use a couple of PNPs in saturation (only 0.3V drop)? Of course,
> the relays give you advantage of complete electrical isolation...
The L293D H-Bridge IC can be had for $4.00 in singles and has two
H-Bridges that can handle 600mA each, they can also be bridged. These
are reallly simple to use, there what I use in the lower current
configuration of my Motor Driver Kit.
>I have a motor control circuit (H-Bridge) and its powered off 6 volts.
>I am using a pic to control the motors, and my problem is that since I
>am only supplying 5 volts and the control, the motors don't go their
>full speed. How can I fix this.
How about that .... finally a question I'm qualified to answer! Your
problem statement is not entirely clear to me, so as I understand it:
1. you have a 6 volt motor,
2. you're driving it via an H-bridge off 5 volt Vcc
3. one side of the motor is biased at 2.5 volts (the mid point of one side
of the bridge)
4. you are reversing the direction of the motor by pulling the other side of
the bridge high or low with a PIC?
Did I get that picture right? That being the case, the motor is running
slow because it never sees more than half the 5 volts across the bridge....
that of couse, less the saturation drops of the bridged transistors
conducting at the given time. If the transistors are in an emmiter follower
config, then you have a fairly large drop across each of them! A
complementary common emmiter topology for each leg of the bridge would be a
lot better.
You can also:
a) Increase the supply voltage to the bridge, and add some level shifters
between the PIC output and the output transistors to get more swing.
b) with the configuration as a full bridge, control *both* sides of the
bridge with the PIC: drive each side of the bridge in the opposite
direction. That way you have full potential across the motor less the Vce
drops.... not as good as having 6 volts, but a t least twice what you now have.
Hope this helps, let me know how it goes.
... Gregg
> > Reed relays are pretty pricey - wouldn't it have been cheaper to
> > use a couple of PNPs in saturation (only 0.3V drop)? Of course,
> > the relays give you advantage of complete electrical isolation...
>
> The L293D H-Bridge IC can be had for $4.00 in singles and has two
> H-Bridges that can handle 600mA each, they can also be bridged. These
> are reallly simple to use, there what I use in the lower current
> configuration of my Motor Driver Kit.
>
I've used it successfully at 1A without any problems. I can't think
of any advantage of reed relays over the 293.
--
Friendly Regards
Tjaart van der Walt
______________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
|+27-(0)11-622-8686 | http://wasp.co.za | TakeThisOuTtjaartEraseMEspam_OUTwasp.co.za |
|______________________________________________________________|
> Ben L Wirz wrote:
>
> > > Reed relays are pretty pricey - wouldn't it have been cheaper to
> > > use a couple of PNPs in saturation (only 0.3V drop)? Of course,
> > > the relays give you advantage of complete electrical isolation...
> >
> > The L293D H-Bridge IC can be had for $4.00 in singles and has two
> > H-Bridges that can handle 600mA each, they can also be bridged. These
> > are reallly simple to use, there what I use in the lower current
> > configuration of my Motor Driver Kit.
> >
>
> I've used it successfully at 1A without any problems. I can't think
> of any advantage of reed relays over the 293.
You have used the L293D or the L293 to 1 Amp? The L293 is rated
at .6 A and the L293D is rated at 1 Amp, or they can be bridged for
double capicity. Can I also ask where you found the L293's if thats what
you used, I haven't been able to find them in anything less then 200 min
order.
> > --
> Friendly Regards
>
> Tjaart van der Walt
> ______________________________________________________________
> | Another sun-deprived R&D Engineer slaving away in a dungeon |
> |WASP International GSM vehicle tracking and datacomm solutions|
> |+27-(0)11-622-8686 | http://wasp.co.za | RemoveMEtjaartTakeThisOuTwasp.co.za |
> |______________________________________________________________|
>
Ben Wirz For Microchip PIC Products including the Simm Stick
development system and the Easy PIC'n Book, as well
Wirz Electronics as Motor Control, Polaroid Sonar Units, and more blw2EraseME.....cec.wustl.edu Hobbyist Robotic & Electronic Supplies, visit: http://cec.wustl.edu/~blw2/
> > > H-Bridges that can handle 600mA each, they can also be bridged. These
> > > are reallly simple to use, there what I use in the lower current
> > > configuration of my Motor Driver Kit.
> > >
> >
> > I've used it successfully at 1A without any problems. I can't think
> > of any advantage of reed relays over the 293.
>
> You have used the L293D or the L293 to 1 Amp? The L293 is rated
> at .6 A and the L293D is rated at 1 Amp, or they can be bridged for
> double capicity. Can I also ask where you found the L293's if thats what
> you used, I haven't been able to find them in anything less then 200 min
> order.
I can't remember offhand. I desoldered them from old MFM hard drives.
The
new hard drives with the voice coils have a Hitachi chip that I also
intend on
trying. I have played quite a bit with the voice coils, and if the
Hitachi chip
can produce what I have abused those voice coils with (2A @ 45Hz), They
will
be pretty robust.
If you still have a few old MFM hard drives lying around, I'd suggest
that you
look closely at the board. They usually have very good surge arrester
resistors
on the power input (ever had surge damage on your modem?).
--
Friendly Regards
Tjaart van der Walt
______________________________________________________________
| Another sun-deprived R&D Engineer slaving away in a dungeon |
|WASP International GSM vehicle tracking and datacomm solutions|
|+27-(0)11-622-8686 | http://wasp.co.za | EraseMEtjaartwasp.co.za |
|______________________________________________________________|
> >Can I also ask where you found the L293's
>
>
> Digi-Key has the LM18293N which is a pin-compatible replacement for the
> L293D with a few improved specs. $4.73 in singles and $1.80 in hundreds.
>
> Cheers, Bob
>
Bob,
As I understand it, the National Part doesn't have the internal
diodes like the L293D and L293's. I don't have a data sheet in front of
me, so please correct me if I'm wrong. Also, the L293D's are common, its
the L293's I have had trouble finding.
Ben,
Ben Wirz For Microchip PIC Products including the Simm Stick
development system and the Easy PIC'n Book, as well
Wirz Electronics as Motor Control, Polaroid Sonar Units, and more RemoveMEblw2EraseMEEraseMEcec.wustl.edu Hobbyist Robotic & Electronic Supplies, visit: http://cec.wustl.edu/~blw2/
> As I understand it, the National Part doesn't have the internal
>diodes like the L293D and L293's. I don't have a data sheet in front of
>me, so please correct me if I'm wrong. Also, the L293D's are common, its
>the L293's I have had trouble finding.
You're right. The LM18293N is a replacement for the L293B, not the L293D,
and it doesn't have diodes.
Sigh, on the robot-board mailing list we are all very familiar with the L293
(and its
beefier TI counterpart the TI75510.(check the number, its from memory)) The
National part that Digikey sells DOES NOT have the snubber diode and so it is
an L293E replacement, not an L293D replacement. If you use the Nat'l part you
need an external snubber network. There is also the Nat'l semi LM18200 which
is more expensive but can handle more current.
--Chuck
----------
From: Bob Blick[SMTP:RemoveMEbblickspam_OUTKILLspamEXECPC.COM]
Sent: Monday, December 02, 1996 11:28 PM
To: Multiple recipients of list PICLIST
Subject: Re: H-Bridge
>Can I also ask where you found the L293's
Digi-Key has the LM18293N which is a pin-compatible replacement for the
L293D with a few improved specs. $4.73 in singles and $1.80 in hundreds.
> You have used the L293D or the L293 to 1 Amp? The L293 is rated
>at .6 A and the L293D is rated at 1 Amp, or they can be bridged for
>double capicity. Can I also ask where you found the L293's if thats what
>you used, I haven't been able to find them in anything less then 200 min
>order.
I've used the L293D which I got from RS Electronics. It was about AU$18 or
so for two units. The L293D lacks the protection diodes. One of the 0.6A
versions comes with protection diodes. One disadvantage of the L293 could
be the voltage drop. I don't know about the L293 but its bigger brother
L298 rated at 4A drops about 2-5 volts. I'm using a couple of L298s bought
from RS at AU$25 each(?). The MOS based H bridges like the LMD18200 probably
have a much lower voltage drop but are way more pricey.
Regards
Prashant
--------------------------------+---------------------------------
Prashant Bhandary | Tel: +61-2-9662 5299
Spatial Information Solutions | Fax: +61-2-9662 5348
Roads and Traffic Authority | Email: RemoveMEprashbTakeThisOuTspamrta.nsw.gov.au
Rosebery NSW 2018, AUSTRALIA | "2b|!2b" - William Shakespeare
--------------------------------+---------------------------------
> From: Prashant Bhandary <EraseMEprashbspamspamBeGoneRTA.NSW.GOV.AU>
>
> [quote cut]
> I've used the L293D which I got from RS Electronics. It was about AU$18 or
> so for two units. The L293D lacks the protection diodes. One of the 0.6A
> versions comes with protection diodes. One disadvantage of the L293 could
> be the voltage drop. I don't know about the L293 but its bigger brother
> L298 rated at 4A drops about 2-5 volts. I'm using a couple of L298s bought
> from RS at AU$25 each(?). The MOS based H bridges like the LMD18200 probably
> have a much lower voltage drop but are way more pricey.
Places like RS Components and Farnell are convenient, well stocked and
comprehensive. The down side is that they are between 2x and 5x as
expensive as a more specialised supplier. Check out the diff between
RS and, say, Zatek for prices on PIC chips in small qty.
The RS catalogue makes an interesting couple of evenings' reading, if
you can get one. They only send you a catalogue if you are going to
spend over $1000 in a year, but I asked nicely so they sent me an
out-of-date catalogue for free.
At 10:43 AM 4/12/96 EST, you wrote:
>Places like RS Components and Farnell are convenient, well stocked and
>comprehensive. The down side is that they are between 2x and 5x as
>expensive as a more specialised supplier. Check out the diff between
>RS and, say, Zatek for prices on PIC chips in small qty.
For PIC chips, yes. For a lot of other chips, the L293 or L298 being good
examples, how do you find a supplier, if one exists? And even if you
consider PIC chips, at one point I was toying with using an SMD PIC 16C84.
The regular PIC suppliers will sell you nothing less than 126 units,
although at a reasonable price. RS sells a single unit at AU$20.
>The RS catalogue makes an interesting couple of evenings' reading, if
>you can get one. They only send you a catalogue if you are going to
>spend over $1000 in a year, but I asked nicely so they sent me an
>out-of-date catalogue for free.
I managed to get an out-of-date one a couple of years back as well after
much cajoling. I even managed to get a CD catalog from them last year but
I can't keep that up year after year. I can understand them being choosy
about giving away their catalog - it is a huge, full colour tome and
probably costs tens of dollars to print but a 2 dollar CD, for Chrissake?
Surely they can toss a few around without feeling the pinch?
Farnell is another story - I rang them up for a catalog and I was told
stiffly that I would be put on their list and sent one when they are
printed. Months passed and nothing happens. Then I discover their web
site in the UK and fill in a form for a catalog and voila! I get one
in the mail!
Regards
Prashant
--------------------------------+---------------------------------
Prashant Bhandary | Tel: +61-2-9662 5299
Spatial Information Solutions | Fax: +61-2-9662 5348
Roads and Traffic Authority | Email: RemoveMEprashbKILLspamrta.nsw.gov.au
Rosebery NSW 2018, AUSTRALIA | "2b|!2b" - William Shakespeare
--------------------------------+---------------------------------
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