[EE] Advisability of using SMD dual-diodes for relay back-EMF clamping

Dwayne Reid <[email protected]>
Newsgroups gmane.comp.hardware.microcontrollers.pic
Message-ID <CAM6OUcECrtPENS5yG=W6jXEn8M=d1Pj5fWTWx84=zhsBBXJkdw@mail.gmail.com>
Good day to all.

I'm working on a retrofit pair of boards for one of our long-time
products.  Basically just a simple serial TX / RX pair to control a bunch
of relays.  Relays are all 12 Vdc with one side of each coil connected to
the 12V Ground.

I've pretty much decided to use 74HC595 chips driving MMBT4403
transistors.  Because these are relay coils, I need to include clamp diodes.

Back when most of my designs were through-hole, I would simply use
individual 1N4005 diodes.  Simple and robust.  However, this board will be
all SMT except for the very few through-hole parts (connectors, etc).

I'm wondering about the advisability of using dual diodes in SOT-23 or
SOT-323 packages.  The specific part I'm considering is the TBAW56 (sot-23)
rated at 215 mA.  The relay coils take about 80 mA with a 13.0Vdc supply.

I am wary about using such tiny parts.  Opinions greatly appreciated!

As an aside, what do people like to use for inexpensive single diodes in
SMT packages.  Something similar to the bog-standard 1N400x family.  What
I'm looking is inexpensive and readily available.

Many thanks!

dwayne
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