I don’t think those topics are too broad to need their own sites at all. I’d be interested to read about all 3. When I read the title I though you were going to propose totally different niches on the same website. But that’s not the case. It’s not like you have a website on running shoes and you wanted to review dentists on the same site! Blogs like wordpress have category pages and I think you could use a different category page for each topic you’re proposing.

I looked at engadget recently and they had an article on an electric car and then a few weeks later the latest graphics card! Totally different niches but still about technology. I think the advantages of having the same site for your topics win out. Just think of all the work for 3 different websites.