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[DPRG] help needed in h-bridge

Subject: [DPRG] help needed in h-bridge
From: Rick Bickle rbickle at swbell.net
Date: Mon Jul 11 12:14:50 CDT 2005

Oops, good point John,
 
With the bases tied together in that configuration, the transistors will
fry.
 
I really would look for another circuit using N channel and P channel
MOSFETS.
There is a schematic for a simple MOSFET based H-Bridge on the DPRG
website under tutorials.
 
Good Luck,
Rick

-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On
Behalf Of jdrumm9015 at aol.com
Sent: Monday, July 11, 2005 12:00 PM
To: rbickle at swbell.net; chwoei at gmail.com; dprglist at dprg.org
Subject: Re: [DPRG] help needed in h-bridge


Horng Woei Chang,
  If you just switched the NPN and PNP transistor locations without
changing the base connections
expect some "magic" smoke to be emitted.  If the NPN was on the bottom
with the emitter connected
to ground the PNP was on the top with the emitter connected to +5VDC you
would have both transistors
on for much of the time when switching.
 
  The original circuit will work for low voltages.  The base - emitter
junctions of the transistors are
exposed to the full reverse bias of the motor supply voltage, if the
bases are driven to the same
voltages as the motor supply.  If that voltage gets much over 7 volts
expect more "magic" smoke to be emitted.  Most biploar transistors only
have about 7 volts reverse bias allowed on the base emitter
before the junctions breakdown.  Without a doubt follow Rick's comments
about using some 
resistors to limit the base current if you are going to use this
circuit.
 
  A very poor circuit to start with, I would suggest continuing your
search and find a better
schematic.
 
John Drummond 
 
-----Original Message-----
From: Rick Bickle <rbickle at swbell.net>
To: 'Horng Woei Chang' <chwoei at gmail.com>; dprglist at dprg.org
Sent: Mon, 11 Jul 2005 10:29:36 -0500
Subject: RE: [DPRG] help needed in h-bridge


I believe that this schematic intends for you to connect something to

the bases of the transistors. Be sure to put some resistance in series

with the transistor bases to limit the base current.



This particular schematic looks to have a problem. I believe that the

NPN and PNP transistors are transposed here. Put the NPN transistors at

the bottom, and the PNP transistors at the top for better function.

Remember that for an NPN BJT, the emitter voltage cannot be higher than

the base voltage - 0.7V. For a PNP BJT, the emitter voltage cannot be

lower than the base voltage + 0.7. Therefore it is more helpful to have

the NPN transistors sink power and the PNP transistors source power.



Rick





-----Original Message-----

From: dprglist-bounces at dprg.org <mailto:dprglist-bounces%40dprg.org>
[mailto:dprglist-bounces at dprg.org <mailto:dprglist-bounces%40dprg.org> ]
On

Behalf Of Horng Woei Chang

Sent: Monday, July 11, 2005 12:21 AM

To: dprglist at dprg.org <mailto:dprglist%40dprg.org> 

Subject: [DPRG] help needed in h-bridge





hello, 



     As i seen H-bridge tutorials in this web, the difference is the

base is not connected but in my case the base is connected , so i would

like to ask if this H-bridge is working ,the picture is attached, and

what if we vice-versa the polarity.

















From: NOBITA





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