Alt-BEAM Archive

Message #06009



To: "'beam@sgiblab.sgi.com'" beam@sgiblab.sgi.com
From: Wilf Rigter Wilf.Rigter@powertech.bc.ca
Date: Thu, 9 Sep 1999 17:48:39 -0700
Subject: [alt-beam] Re: motor driver: h-bridge or IC?




I don't like the big voltage drop (~2V) on the L293 and L298 chips. They run
hot and are really too inefficient to be used applications below 12V. On the
other hand a mosfet h-bridge is perfect for 5V applications. The mosfets
have high input resistance and low forward voltage drop depending on the
"on" resistance. Only 4 components are needed for a full h-bridge and these
are available for free if you are resourceful and willing to de-solder
components. A dead 80M Conner and similar IDE harddrive typically has
6-10 complementary IR mosfets often in 4 pin DIP packages. I have found some
with part numbers IRFD123 (N-channel) and IRFD9020 (P-channel). The specs
for those parts are approximately 0.2 ohm "on" resistance and max current of
1.2A @30V. They can comfortably drive hobby servos with minimal losses.
Attached is a schematic of the mosfet h-bridge ready to be attached to a
Bicore or microcore.

enjoy

<>

Wilf Rigter mailto:wilf.rigter@powertech.bc.ca
tel: (604)590-7493
fax: (604)590-3411

> -----Original Message-----
> From: Dan Larson [SMTP:dlarson@citilink.com]
> Sent: Thursday, September 09, 1999 2:54 PM
> To: beam@sgiblab.sgi.com
> Subject: Re: motor driver: h-bridge or IC?
>
> If you want a real h-bridge for battery powered
> applications, get an L293D (SGS Thompson).
> It is rated up to 600mA, *dual* hbridge,
> and has back emf diodes built in.
>
> There is also the L298N which is good up to 3A.
>
> You can get them at Mouser http://www.mouser.com
> for US $2.12 each (The L293)
>
> 74HCT245s might be fine for smaller current
> motors, but anything bigger cries out for
> a real h-bridge chip. Making your own h-bridges
> from discrete transistors (I've done it) is
> too much trouble.
>
>
> Dan
>
> On Thu, 09 Sep 1999 14:47:39 -0400, SG wrote:
>
> >Hi all,
> >I think one of my 6 transistor h-bridges burned
> >out (i hope thats what the problem is anyway)
> >and rather than solder some more transitors together, i thought i might
> try
> >two 74HCT245's stacked.
> >Does anyone know if this will be enough to power standard servo's?
> >Thanks!
> >-Sparky
> >
> >
>
>
>



Attachment: FETBRIDGE.gif

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