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'[OT] Re: Relay problem..'
|>> Now if you start to be clever, you use an Allegro or equivalent
>> ULN4003 which is *designed* for this application and includes the
>> diodes. Of course with the 7406 you had 5 spare drivers and with the
>> 4003 you have 6 spare.
I think he meant '2003'. Its a nice little 16 pin package with 7 darlington
transistors, integrated base resistors and clamping diodes. Its big brother
is the uln2803 - 18 pins with 8 stages.
The 2003 and 2803 parts are *CHEAP* and robust.
If you are running out of PIC pins, do consider the TI parts TPIC6B595. Its
a shift register with on-board data latch and 8 MOSFET drivers rated at 150
mA continous each. Its bigger brother TPCI6595 (note the missing 'B') is
good for about 250 mA per channel. The two parts are pin compatible EXCEPT
that pins 1 & 20 are ground on the bigger part and unconnected on the
smaller part. I always tie pins 1 & 20 to ground so that I can use either
part. The TPIC6C595 is pin compatible with the standard HC595 but good for
about 125 mA per channel. Note that you can parallel multiple outputs for
more current. One of my products uses 3 TPIC6B595's to control 6 solenoids
at 1/2 Amp each - I used 4 outputs in parallel times 6. I was leary of this
at first but TI's tech support FAE assured me it was safe to do so and I
have had NO failures in over 3 years of production. Way cheaper than relays!
Dwayne Reid <planet.eon.net> dwayner
Trinity Electronics Systems Ltd Edmonton, AB, CANADA
(403) 489-3199 voice (403) 487-6397 fax
Celebrating 15 years of Engineering Innovation (1984 - 1999)
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