Re: Switched Mode Power Supplies
Whilst I admire the can-do attitude on this forum, I would caution that boost converters are works of the devil, especially if they have a high output to input voltage ratio.
The control of the output voltage is non trivial - you will likely end up with strange behaviour or blown devices if you dive in without simulated design first. I whole-heartedly recommend the LTSPICE simulator available from Linear Technology (now owned by Analog Devices). Its easy and intuitive to drive and there are lots of resources that come with it. Its also free for non-IC design use, even commercial.
Their own chips, some of which are excellent and easy to use, are all modeled accurately, so you should be able to get something going easily. That way you can experiment without burning pound notes or fingers.
90V 10mA is an unusual output these days, so many modern IC's will struggle to control the output voltage without mis-behaviour. The Unitrode IC are general purpose and can be made to work in these applications as long as you aren't too ambitious about size and efficiency and keep the switching frequency low (i.e. 10's kHz, not MHz). I would avoid Bipolar switching devices - MOSFETs are much easier.
EMC is another matter - boost converters make junk on their output (the output current is dis-continuous) and a extra L-C filter and some screening are likely necessary for radio use.
Kevin.
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