> Short version: What is the absolute minimum footprint driver circuit
> (NOT
> SMT) that will work from an Open Collector output with a 4.7K pull
> up to +5
> (PC parallel port nStrobe pin) and drive a small OMRON G5LE-1 DC5
> which has
> a 5 volt, 63 Ohm coil?
>
> Long version:
>
> I have a PCB that I would like to squeeze a bit more functionality
> into, but
> I have almost no real-estate available. I've managed to put a PCB
> mount
> relay on the underside of the board (with other components on the
> top) by
> fitting it's few through hole leads in between other stuff.

5V, 63 ohm = 80 mA.
Drive from the pullup will be (Vstrobe-1Vbe)/4k7 ~= (5-0.6)/4700 ~=
0.9 mA

With say 0.5 mA drive you need a transistor current gain (Beta) of
80/.5 = 160 which is  achievable with many of the more capable small
transistors. I'd use BC337 here but there are many others.

The 2N2222 is a bit low Beta as is at 100 min at 150 mA.
It would quite possibly work but ... .

An appropriate small N Channel MOSFET would work with ease as the
voltage gain is close to infinite for practical purposes.
You want Vgsmin comfortably more than the driver off (low) voltage and
the FET suitably enhanced (on) at Vgs = 5 V.
Not a hard spec to meet. Using a Digikey parametric search would
probably turn up many parts.

Either  a FET or bipolar could be added with NO other components and a
TO92 pkg probably meets your spec.

Using Digikey parametric search on MOSFET, N Channel, TO92, 12-100V,
200 - 1000 mA gave 4 pages of results.

________

2N7000FS $US0.26/1, $US0.13\52/100, $US0.0572/1000 is a typical
starter for 10 points.
Current rating a bit low but would work.
Rdson about <= 2.5 ohms at your load at 100C which sounds (and is)
terrible BUT at your load current that gives 0.2V drop which is fine.
Dissipation is minimal.

        http://www.fairchildsemi.com/ds/2N/2N7000.pdf

___________

BS170_D27ZTR-ND $US0.075/2000
Looks near ideal

        http://www.fairchildsemi.com/ds/BS/BS170.pdf

Watch the Vgsonmin which is too GOOD ie low at 0.8V min, 2.1V typical,
3V max. Need to be sure that driver pulls below 0.8V always.


Many more but that's an OK start.



        Russell










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