Subject:
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Re: Help with converting voltage on circuit board
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Newsgroups:
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lugnet.robotics, lugnet.technic
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Date:
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Tue, 11 Apr 2006 21:09:39 GMT
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Viewed:
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2825 times
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In lugnet.robotics, Danny Staple wrote:
> In answer to Davids question about the 4v connector (using the old Lego
> electrical connector), it looks more likely to be just a straight 4v supply
> output, which is not controlled. Were it an input, the devices that are
> compatible are pitiful battery boxes which would probably not handle the load of
> more than one motor very well. Equally, I do not remember needing an input
> voltage there when using it at school, although that was about 12-15 years ago.
>
> However, since the supply goes there, before going to any of the H-bridge
> transistors (the geometry of the tracks looks fairly straight forward on that),
> then maybe you could cut the tracks coming from the main supply to there, or at
> least keep a common ground, and put in 12v supply that would handle the load.
> However, I still repeat my concern about the power transistors in the bridges
> handling that larger voltage.
>
> Danny
Hi Danny,
If we supply +12V to the top of the transistors, the drive circuit will most
likely not be able to block those transistors completely (unless said drive
circuit has an open collector structure with a pull up to the emitter of the
transistors).
I would not be too concerned with the voltage damaging the transistors. Most can
take up to 60V. The problem may be the amount of power that the new application
would require them to dissipate (power = voltage drop accross the transistor X
current flowing through it). Running a train motor (or two or three) may result
in a high power dissipation... We may need a heat sink.
One other class of components I would worry about are the capacitors. If they
used caps that are rated at 6V and we apply 12V to them, well things would get
"very interesting".
I'll have a closer look at the circuit tonight when I get home...
Greetings,
David
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