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[DPRG] Rick's H-bridge problems

Subject: [DPRG] Rick's H-bridge problems
From: IanR IanR at rotalink.com
Date: Sat Sep 25 04:29:55 CDT 2004

I'm trying to use this design to drive via PWM, but seem to be struggling, I
think the transistors are taking a very long time to switch on and was
wondering if you had any thoughts on this. I.e. Have I probably done
something wrong, do you know what frequency the Design will work up to etc.



-----Original Message-----
From: Rick J. Bickle [mailto:rbickle at swbell.net]
Sent: 30 August 2004 15:45
To: 'Farhan K.'; dprglist at dprg.org
Subject: RE: [DPRG] Rick's H-bridge problems


One of the reasons I designed this H-bridge circuit was that it does not
have a "once only" mode. It should not be able to short the rails,
regardless of the steady state inputs. If you leave an input floating,
it may cause one side of the bridge to oscillate.

As a general rule, never leave inputs floating.
BTW: This exact H-Bridge has been running my robot drive motors at 4A
for quite a while.


-----Original Message-----
From: dprglist-bounces at dprg.org [mailto:dprglist-bounces at dprg.org] On
Behalf Of Farhan K.
Sent: Sunday, August 29, 2004 4:27 PM
To: dprglist at dprg.org
Subject: [DPRG] Rick's H-bridge problems

Hello all.

After having failed with trying to get two channels of L298 to work in 
parallel to give me current capacity of 4A, i abandoned that idea coz 
everything i was doing was right and still the L298 melts down :( ! .
anyone ever really got it working practically?

As Rick suggested, I found the h-bridge schematic in his presentation
followed it using the IRF9540 and IRF540 but still this was more pain.
solution seems to be very sensitive to any wrong input, i (accidently)
one of the inputs floating and next minute found two of the IRFs
What are the considerations I should take into account when trying to 
operate that circuit?
I am operating it at 24V.

Back to L298, Ive heard that two L298s can also be paralleled to give
current (4A+4A), any comments on that?


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