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'[EE] H-bridge problems'
2003\03\09@185754 by John Dammeyer

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Hi,

You can't just use the inverse of the drive signal for one leg of the
bridge to turn off the other leg of the bridge.  There's a period of
time where both devices will conduct and then you end up with a short
across the power supply.  Hence the burned out transistors.  And as the
transistors get warm,  they sometimes have the tendencies to stay on a
little longer exacerbating the problem if you design for and work cold.

I had a Paper Tiger dot matrix printer that had an H bridge controlled
by the uC.  It would, with really long listings blow the transistors
(TIPxxx).  I wasn't able to change the software running the H-Bridge so
the solution was a fabricated heat sink and a small fan blowing on the
heatsink. That kept the transistor temperature low and although it made
the printer a bit louder,  got rid of the problem.

The easiest way is to drive each leg separately and then switch one off,
delay and then switch the other on.  If you can't do that for lack of
I/O then you need to add external logic to delay the turn on of each
driver transistor but allow the turn off to happen quickly.

Cheers,

John Dammeyer


Wireless CAN with the CANRF module now available.
http://www.autoartisans.com/products
Automation Artisans Inc.
Ph. 1 250 544 4950


> {Original Message removed}

2003\03\09@191157 by Morgan Olsson

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Hej RADAR Engineering Team. Tack för ditt meddelande 00:32 2003-03-10 enligt nedan:
>I am using pwm to an H-bridge to drive a DC motor.  I chose TIP145 and TIP140 because they can handle 15A max.  I plan on using 2n5210 switching transistors to switch the TIPs.  I want to switch at ~18-22kHz.  My first question is can the 5210s switch fast enough (I could not find switching characteristics) if not does anyone have a suggestion?  I will be running the bridge at 48VDC, so the transistor must be able to handle it.  Also, I used 2n2222s to test the circuit (using a 12VDC source) and I am steadily burning up transistors.  I have attached the schematic.  If anyone is able to help I would appreciate it.
>Thank you,

< Schematic1.JPG >

Add "free-wheeling diodes"  that means diodes across each of the four power transistors CE to protect them from reverse voltage, that the motor inductance couse when you switch them off.

I have not analyzed your design thoroughly, by i think at least for th eupper trannys you should add BE resistors of a couple hundred ohms to make them switch off fast enough.

/Morgan
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Morgan Olsson, Kivik, Sweden

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2003\03\09@214412 by Bob Blick

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Hi Tom,

Interesting that you've chosen to copy my H-Bridge but didn't use my
cool schematic or give me credit. No problem, but you really should visit
my site at least to read the extensive notes and see the real schematic
which doesn't have the errors in it yours does.
http://www.bobblick.com/techref/projects/hbridge/hbridge.html

Cheerful regards,

Bob



On 9 Mar 2003 at 18:32, RADAR Engineering Team wrote:

> I am using pwm to an H-bridge to drive a DC motor.  I chose TIP145 and TIP140 because they can handle 15A max.  I plan on using 2n5210 switching transistors to switch the TIPs.  I want to switch at ~18-22kHz.  My first question is can the 5210s switch fast enough (I could not find switching
characteristics) if not does anyone have a suggestion?  I will be running the bridge at 48VDC, so the transistor must be able to handle it.  Also, I used 2n2222s to test the circuit (using a 12VDC source) and I am steadily burning up transistors.  I have attached the schematic.  If anyone is able
to help I would appreciate it.
{Quote hidden}

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2003\03\09@235702 by RADAR Engineering Team

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I was under the impression that the TIPs already had the diode from CE.  Even though, I have tried the diodes and it did not seem to help (I will add the resistors and try it again though, Thanks for the time and assistance).

Bob, I did not use your "cool" schematic because I was simulating it in PSPICE and that is just how it ended up looking.  I do thank you for the help (and the great web page).  
When I simulate I do get a mean transient response.  There is a terrible short when the actual switching takes place.  I tried a couple approaches to get rid of some of the spike with little success.  I am haveing a hard time seeing the difference from the PSPICE schematic and your web picture.  Please help!

Thanks for everyones assistance,
Tom

RADAR Engineering Team
Engineering Dept.
Lake Superior State University
650 W. Easterday Ave.
Sault Ste. Marie, MI 49783

PH: 906-635-2692
FX: 906-635-6663

.....radarKILLspamspam@spam@lssu.edu

>>> Morgan Olsson <dlistspamKILLspamMORGANSREGLERTEKNIK.SE> 03/09/2003 7:06:24 PM >>>
Hej RADAR Engineering Team. Tack för ditt meddelande 00:32 2003-03-10 enligt nedan:
>I am using pwm to an H-bridge to drive a DC motor.  I chose TIP145 and TIP140 because they can handle 15A max.  I plan on using 2n5210 switching transistors to switch the TIPs.  I want to switch at ~18-22kHz.  My first question is can the 5210s switch fast enough (I could not find switching characteristics) if not does anyone have a suggestion?  I will be running the bridge at 48VDC, so the transistor must be able to handle it.  Also, I used 2n2222s to test the circuit (using a 12VDC source) and I am steadily burning up transistors.  I have attached the schematic.  If anyone is able to help I would appreciate it.
>Thank you,

< Schematic1.JPG >

Add "free-wheeling diodes"  that means diodes across each of the four power transistors CE to protect them from reverse voltage, that the motor inductance couse when you switch them off.

I have not analyzed your design thoroughly, by i think at least for th eupper trannys you should add BE resistors of a couple hundred ohms to make them switch off fast enough.

/Morgan
--
Morgan Olsson, Kivik, Sweden

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2003\03\10@025944 by hael Rigby-Jones

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> -----Original Message-----
> From: Morgan Olsson [SMTP:.....dlistKILLspamspam.....MORGANSREGLERTEKNIK.SE]
> Sent: Monday, March 10, 2003 12:06 AM
> To:   EraseMEPICLISTspam_OUTspamTakeThisOuTMITVMA.MIT.EDU
> Subject:      Re: [EE] H-bridge problems
>
> < Schematic1.JPG >
> Add "free-wheeling diodes"  that means diodes across each of the four
> power transistors CE to protect them from reverse voltage, that the motor
> inductance couse when you switch them off.
>
> I have not analyzed your design thoroughly, by i think at least for th
> eupper trannys you should add BE resistors of a couple hundred ohms to
> make them switch off fast enough.
>
> /Morgan
>
That's exactly what jumped out at me when I looked at it.  There is nothing
to switch off either the lower or the upper transistors quickly.  Some form
of reverse voltage control such as freewheeling diodes is pretty essential
of course.

Regards

Mike


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2003\03\10@065016 by Ray Gallant

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Someone from another forum is looking for a similar design.  Can I send them
to your site Bob?  {slewrate}

{Original Message removed}

2003\03\10@123907 by Bob Blick

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part 1 2437 bytes content-type:text/plain; charset=iso-8859-1 (unknown type 8bit not decoded)

RADAR Engineering Team said:
> I was under the impression that the TIPs already had the diode from CE.
> Even though, I have tried the diodes and it did not seem to help (I will
> add the resistors and try it again though, Thanks for the time and
> assistance).

Yes they do have the diodes and pinch-off resistors. See the attached
internal schematic of the TIP12x series darlingtons. Others in that series
are quite similar.

> Bob, I did not use your "cool" schematic because I was simulating it in
> PSPICE and that is just how it ended up looking.  I do thank you for the
> help (and the great web page).

I just assumed you got it from someone elses website and wondered why they
decided to redraw it etc.

> When I simulate I do get a mean transient response.  There is a terrible
> short when the actual switching takes place.  I tried a couple
> approaches to get rid of some of the spike with little success.  I am

When you say switching do you mean toggling from A-on to B-on? You can't
do that without adding a small delay. Turn-off takes longer than turn-on,
so if you toggle the two sides with no delay you'll get that.

> haveing a hard time seeing the difference from the PSPICE schematic and
> your web picture.  Please help!

You should have a big capacitor on the power input because otherwise you
get voltage spikes each time you turn off, as the motor dumps its stored
energy. Batteries are not capacitors. Especially at the end of a long
wire.

On a related note, that bridge, even with TIP14x transistors, is only good
for 10 amps, or 40 volts, or 200 watts, whichever comes first. The losses
of darlingtons is fairly high. It also will not run at 20KHz. Even if you
add extra pinch-off resistors you can't get to the inner base, so the
turn-off speed is limited.

I've used it with TIP14x parts at 18 volts, 10 amps with 300Hz PWM and it
runs quite cool and does not fail. It is meant to be a low parts-count
bridge and there's no way you can make it do what you want.

You should look into MOSFET high-side driver chips if you want a simple
circuit that can make a bridge that does what you want. I like the IR2112
but there's also a nice LT chip.

Cheerful regards,

Bob Blick



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part 2 6539 bytes content-type:image/gif; name="tip12x.gif" (decode)


part 3 2 bytes
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