[chbot] H-Bridge (was Re: Sensor Information)

[Jim Ronald]

Thanks for everyone's input.  I ended up taking the easy way out and ordered 
a SaberTooth 2x5.

Thanks
Jim


----- Original Message ----- 
From: "Richard Jones" <rjtp at ihug.co.nz>
To: "Christchurch Robotics" <chchrobotics at lists.linuxnut.co.nz>
Sent: Wednesday, March 25, 2009 9:54 PM
Subject: Re: [chbot] H-Bridge (was Re: Sensor Information)


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> Charles circuit from Mark Tilden has a significant benefit in that it will
> run from 3.3V drive, which may be a little tricky for FETs.
> The little football robots that Stuart brought in a few months back used a
> similar cct but relied on the software to keep the smoke in!
> Richard
>
>
> On Thu, 26 Mar 2009 11:06:31 +1300, Charles Manning
> <manningc2 at actrix.gen.nz> wrote:
>> Herewith a reasonably good circuit for a simple H-bridge, roughly done
> but
>> the
>> idea is there.
>>
>>
>> It was designed by Tilden (the BEAM guy) and we've used them a bit.
>>
>> How it works:
>>
>> The inputs go to the resistors at the left and right of the schematic.
>>
>> Let's consider an input on R1. When it does high this causes T6 to
> conduct
>> which, in turn turns on T4 and T2. causing the motor to be powered in one
>> direction.
>>
>> When R3 is taken high, then T7, T5 and T1 conduct, turning the motor the
>> other
>> way.
>>
>> If all the above were turned on simultaneously there would be a short
>> circuit,
>> so T3 is added as an "anti-smoke" transistor. If R1 input goes high then
>> so
>> does R4, causing T3 to turn on which forces T7 off, thus saving the day.
>>
>> This circuit is common emitter so there is no voltage loss across the
> main
>> driving transistors.
>>
>> You need to experiment a bit with resistors. I would suggest starting
> with
>> R1,
>> R4, R3 all being 10k and R2 being 100 ohms.
>>
>> R1 and (R3 + R2) control the maximum current so changing these to 1k
> would
>> increase the current.
>>
>> T1,2,4,5 are the main power transistors.
>>  T3,T6 and T7 can be low power devices.
>>
>>
>> Have fun.
>>
>> -- CHarles
>>
>>
>> On Wednesday 25 March 2009 17:55:12 Hanno Sander wrote:
>>> Agree with Charles- from personal experience!
>>> Don't use the L293 for low voltage (<12V) systems!  You'll lose too much
>>> voltage to heat the device.  Best bet is probably to make your own
>> h-bridge
>>> - it's not that hard...
>>> Hanno
>>>
>>> 2009/3/25 Charles Manning <cdhmanning at gmail.com>
>>>
>>> > I would not put the L298 high on the list because it is a common
>>> > collector device, just like the L293.
>>> >
>>> > The internal configuration of these devices means that the output
>> voltage
>>> > does not swing all the way to the rail and you lose approx 1.5 to 2
>> volts
>>> > in the driver chip. This turns into heat, but also means that your
>> motor
>>> > does not get driven as hard as it should meaning that it does not get
>>> > enough Weetbix to win that Sumo competition. That is perhaps not too
>> much
>>> > of an issue when you're using 12V or more input, but obviously
>> throwing
>>> > away 1.5V or so is bad news for low voltage systems.
>>> >
>>> > Many modern HBridge designs are "rail to rail" and do not suffer this
>>> > problem.
>>> >
>>> >
>>> >
>>> >
>>> > On Wed, Mar 25, 2009 at 3:54 PM, Andrew Errington <
>>> >
>>> > a.errington at lancaster.ac.uk> wrote:
>>> >> I actually like this design:
>>> >>
>>> >>
>> http://www.mcmanis.com/chuck/Robotics/tutorial/h-bridge/bjt-circuit.html
>>> >>
>>> >> Because the opto circuit is very elegant (it combines optical
>> isolation
>>> >> with 'smoke-free' logic).  I've never built one as I was not able to
>>> >> find a fast enough opto-isolator to do high-frequency PWM.   It may
>> be
>>> >> that that is a non-issue however.
>>> >>
>>> >> Good luck with whatever design you choose.
>>> >>
>>> >> Andrew
>>> >>
>>> >>
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