>So you want 24v to 40v in, 12v @ 3A out?
Not quite.  I need is as low a input voltage as I can
get, and then up to about 35-40 max. Say the input range
is  7Vin to 40Vin output needs to be 5v and 2-3A.

>Getting close to 40v input means the buck diode needs
>to be rated for 60v, which is starting to push the
>common type schottkys. I can get TO220 60v 16A diodes
>for about $1.10 USD, provided you take adequate
>measures for automotive spikes etc that type would do.

I think the actual max Vin I'd see would be 30v.

>It will only be about 1.5A input so maybe a cheap
>n-channel FET could be adapted, or even go with a
>low-tech (cheap) bipolar like the BD204 with low sat
>spec (and maybe a driver transistor) would work.

1.5a input or output?

>I'd like to give it a go in the simplest 2-tran
>config I can manage, will be a bit of fun. What sort
>of requirements do you have for;


>* total size

Well if this works its replacing one TO-220-5.
So the smaller the area the better.

>* inductor type

No pref.

>* cost sensitivity

CHEAAAAAAAAAP er ah total under about $5

>* quantity

No idea.

>* input filtering

source voltage will be regulated dc ie auto alternator/reg

>* will it be compared with a specific chip?

Yup. The mark to beat is the Max727ECK

Dave

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