Alt-BEAM Archive
Message #01417
To: beam@corp.sgi.com
From: Terry Newton wtnewton@nc5.infi.net
Date: Wed, 10 Mar 1999 00:11:41
Subject: [alt-beam] Re: Surface mount H-bridge chip
At 12:47 PM 3/10/99 +1300, Justin wrote:
>I don't know if you already know about this, but I was browsing through
>a big component catalog yesterday, and came across an h-bridge in a
>surface mount packahe (8 lead SOT-223).
Yes, they are wonderful things!
>I'm not a big user of h-bridges, so I don't know if it's suitable for
>BEAM, but comparing the schematics shows that this h-bridge is just the
>four central transitors (2 npn and 2 pnp) thus, you'd need to add the
>other two transistors yourself to take the four inputs down to the more
>useful two.
Actually, the transistors inside have sufficient gain by themselves,
no additional transistors are needed if the driving circuit can tolerate
about a 1.5K load, good for a few hundred milliamps. Not an emitter
follower but a 4 transistor H-bridge. Ascii ahead use fixed font...
Zetex Active-Low H-bridge 11 = off 01 = goes one way
------------------------- 00 = poof 10 = goes the other way
_______
.-----|1| |-----1.5K---< In B
Ground o-----|-----| | |-----.
| .--| | |-----|-----o + Supply
In A >--1.5K-|--|--|_|_____|--. |
| | | |
`--|---1K--------*--|-----> 'A Motor
`-------1K-------*-----> 'B Outs
Zetex Active-High H-bridge 00 = off 01 = you know..
-------------------------- 11 = smoke
_______
In B >----1.5K-----|1| |---1K---*-----> 'A Motor
Ground o-----------| | |--*-----|-----> 'B Outs
In A >----1.5K-----| | |--|-----|---o + Supply
.--|_|_____|--|-----'
| |
`------1K-----'
Active-Low would be appropriate for microcore walkers, Active-High
for PICs, logic and stuff but depends on what you need. Size the
resistors to fit your driver circuit and load, values shown would
be typical for a chip driving a small motor.
Making 'em non-smoking takes more resistors and diodes,
for the Active Low design, connect..
.----------|<|------< from Out B of bridge
In A >---1K--*---470------> to In A of bridge
.----------|<|------< from Out A of bridge
In B >---1K--*---470------> to In B of bridge
Diodes = 1N34 or 1N914/4148 (pick for low forward if possible)
For the Active-High design - turn the diodes around.
>The price is quite high (about US$3.50), but if anyone is interested I
>can copy out the stats, and you can find out if they're suitable.
Digikey carries them, ZHB6718-ND for $5.03 each. A bit pricey, but
man they're cool! Even though smt, much easier to free-form than
discrete bridges. And so tiny!
>If you want to look for it yourself, it's the ZHB6790, description: SM-8
>Quad packaged transistors. Manufactured by Zetex.
>There is also the ZHB6718, which is the same thing, except the
>transistors won't carry as much.
For low voltage operation, 5 volts or less, either part is OK. Both have
the same current rating of 2 amps (!) but the 6790 is 20 volts and has
slightly more gain. While surfing the Zetex site double checking my specs
I noticed a jewel - the Zetex 6702 with darlington transistors, same
circuit but the resistors can be much larger, 10K or more.
Terry Newton
------------------------------------------------------------------------
eGroup home: http://www.eGroups.com/list/alt-beam
Free Web-based e-mail groups by eGroups.com
Home