Jinx wrote:
> I need to step-up 13V to 18-24V for a motor that draws 0.75A at 13V
> under load. I've some MC34063s lying around and they look as though
> they would do the job. But first, questions.....
>
> ...
>
> Figure 11 looks the business, what suggestions for the transistor,
> Schottky, base resistor and choke ? To hand I've got 2N3055,
> MJE3055, TIP3x / 4x, 1N5819, BAT46 etc in the semis dept, but
> nothing in chokes

I didn't follow the links, but since you're stepping up the voltage you will
need a low side switch.  At these voltages a N channel FET would be more
appropriate for the switching element.  In this range Rdson will be around
10mohms, resulting in much lower voltage drop and therefore power
dissipation than a bipolar transistor.  You shouldn't even need a heat sink.

As for inductors, I always start with Coilcraft.  They have a nice product
line of quality components, are reasonably priced for production quantities,
and are good about samples.  My only gripe with them is the first quantity
price break is usually well beyond what I'm willing to buy for prototypes or
small production runs.  I might be willing to buy 10-50, but not 500.


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