> From: Jon Baker <jon@MARZIPAN.DEMON.CO.UK>
>
> Does anyone know of a dc/dc convertor that will change 5 into 15v?

See Analog Devices (ADP series), MAXim and Linear Technology.

>  All the  ones I found so far only go up to 12 and that's not good enough
for
> programming with.

See step-down  DC-DC conv. with 15v fixed output or with adjustible output.

> Failing that does anyone know how to build switchedmode psu's?

 There are many beautiful chip, why do it yourself?

>What maths > is involved in deciding frequency and inductance?

 In all datasheets you can find the structure af dc-dc conv. and
calculating its parameters.

Alex Torres, Kharkov, Ukraine (exUSSR)
altor@chat.ru
2:461/28 FidoNet
http://www.geocities.com/SiliconValley/Lab/6311