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PICList Thread
'Cheap Motor drivers [OT]'
1997\09\10@153737 by lilel

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I'm looking for a cheap half bridge driver, perhaps a MOSFET driver,
that will take a 5 volt input signal and drive a 24 volt motor both
directions.

I discovered the Telcom semiconductor TLC4427 in an old Nuts and
Volts article, and it looked like just what I needed.  Hook up
ground, two 5 volt signals, and a higher voltage (up to 22 volts, it
sez here) and you have two pins able to drive a small DC motor.

Not so fast.  At 18 volts, the H-bridge shorts out and renders the IC
into a small 8-pin paperwieght.  Even with a 13 volt power supply
with a lot of ripple, these things last a few seconds before they
blow, with no load.  I think they are worthless at anything over 6
volts.

What do you PICsters use to drive relays and small DC motors?

Best Regards,

Lawrence Lile

1997\09\10@163952 by lilel

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Todd,

> >What do you PICsters use to drive relays and small DC motors?
>
> You might take a look at the ULN2003A.

Looks good, except it's an open collector output.  I'm trying to
drive a small motor forward and reverse, so I need to find something
that can hook up to the motor in an H-bridge configuration.  So far
no luck.


Best Regards,

Lawrence Lile

1997\09\10@163958 by Pierce Nichols

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On Wed, 10 Sep 1997, Lawrence Lile wrote:
>
> What do you PICsters use to drive relays and small DC motors?

       You can build yr own H-bridge out of discrete transistors -- a
little more expensive than an appropriate IC at low power, but it is the
way to go for higher powers. An H-bridge is a really simple circuit --
it's somewhere in the Art of Electronics along with a complete discussion
of analysis and transistor selection. If you can code assembler, you can
certainly build an H-bridge.

       Pierce Nichols

1997\09\10@164003 by Lawrence Lile

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At 02:35 PM 9/10/97 +0000, you wrote:

>What do you PICsters use to drive relays and small DC motors?

You might take a look at the ULN2003A.  Inexpensive and available.  It
contains seven transistors, each able to carry up to 500mA (from memory).
On the relays, make *sure* to use the diode across the coil to capture the
collapsing field.  I believe the ULN2003A datasheet is on our web site in
the EDE1200 section.  http://www.netins.net/showcase/elab

-Todd Peterson

E-Lab Digital Engineering, Inc.
 "Embedded Control & Integrated Circuit Solutions"

EDE300 IC -  Stamp I/O Expander & PC Interface IC
EDE700 IC -  Serial to LCD Interface IC
EDE1200 IC - Stepper Motor Controller
EDE1400 IC - Serial to Parallel-Printer IC

http://www.netins.net/showcase/elab

1997\09\10@193510 by Mike Keitz

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>'S ok.  I don't need to handle near that much power.  I'm looking for
>something that will run a motor that uses 200 milliamps at 24
>volts.  I'm trying to avoid building a discrete H bridge cuz
>SOMEBODY has done this before and put it obn a chip.

If you're getting the 24V from a line-frequency transformer, connect the
motor to the transformer secondary through a triac.  Trigger the triac on
positive half-cycles to make the motor go forward, on negative
half-cycles to make it go backward.  Saves having to rectify the AC in
the first place.  It doesn't get much cheaper than this, should also be
rather durable.  The motor only gets half-cycles of power so it should be
one built for a lower voltage if you need rated speed and torque from it.

1997\09\11@120849 by David W. Duley

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In a message dated 97-09-10 16:44:12 EDT, you write:

<<
        You can build yr own H-bridge out of discrete transistors -- a
little more expensive than an appropriate IC at low power, but it is the
way to go for higher powers. An H-bridge is a really simple circuit --
it's somewhere in the Art of Electronics along with a complete discussion
of analysis and transistor selection. If you can code assembler, you can
certainly build an H-bridge.

        Pierce Nichols
 >>
Hello Pierce,
In theory the H bridge is simple, but the simplicity stops when you actually
try to build one.  Check out the circuit for the LM18245 from National.
It becomes very complicated when you try to use 5 volts to switch anything
greater than 5 volts.  If you turn on a Mosfet with 5 volts that is what you
get out of a P channel Mosfet.  The 18245 uses a DC/DC converter to step up
the control voltages.
If you are running simple 3 to 6 volt motors then I agree with you.  You can
kill alot of transistors trying to get one working though.
An H bridge, if not connected right the first time, will incinerate in a
fraction of a second.
Been there...Done that...

Dave Duley
V.P. DreiTek Inc.
http://www.dreitek.com

1997\09\12@015101 by Josef Hanzal

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< snip >

> If someone knows of a low drop (Rds) MOSFET h-bridge, please let me know.

How about Thomson's L6203:

Supply voltage 48 V max
Current 3 A max
Rds(on) 0.3 ohm typ. (0.55 max)
Inputs TTL compatible
Operating frequency up to 100 kHz
Specified reverse source-drain diode
Short circuit protected
Thermal shutdown
Multiwatt 11 package
Except I don't know if you consider it still cheap. Here in Czech in costs
about $4 in single quantities.

Primary area of application is in driving bipolar stepper motors, but will
certainly suit for DC motors as well. For lower currents see L6202 and L6201.

Regards

Josef Hanzal

1997\09\12@092420 by lilel

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Josef said,

> How about Thomson's L6203:
>
> Supply voltage 48 V max
> Current 3 A max
> Rds(on) 0.3 ohm typ. (0.55 max)
> Inputs TTL compatible

> Except I don't know if you consider it still cheap. Here in Czech in
> costs about $4 in single quantities.

Mouser Electronics wants $12.50 US for one, but they are high.

Best Regards,

Lawrence Lile

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