How do I protect my idea before presenting to a large company? First of all some background info:

I did a PhD in Electrical Engineering. Basically during my PhD I developed a concept that is now being trialled by two companies. One is very small, but one is a large multinational. The companies that were involved with my department were not interested in patenting the idea. I was forced to publish it. I don't really care about publish/patent, as it will still be great if my PhD gets used in real life.

The problem is now that at the end of the year I dont have a job. I dont publish many papers, whereas others here seem to be able to publish 5 or 6 a year. Yet, my PhD is the only original idea that is being trialled by industry (that I know of) from our group.

I now have another idea that I think is just as good and would probably be trialled by industry. The idea is very simple and requires basically just 1 op-amp. I want to present this to external companies. I am visiting a very large one in November who were interested in using my PhD.

My goal is to use this idea, combined with my PhD, to try to get external private funding, or a job that means I still have a job in this city. I don't really have any skills, all I did was a PhD, which was a really simple idea and made a few circuits to prove it in a lab. If I had experience in designing proper circuits for real products I would have probably been able to get a job elsewhere. My only skill is that I can show that I can analyse the current state-of-the-art, and generate improvements using very simple concepts (which are also novel).

My last resort is to publish it. Again I don't care if I publish it or not, but I already published 13 papers in 3 and a half years. Who cares if I publish 1 more when there are others with 25. I just want to maximise my chances of getting a new job since according to this group's standards I am 'unproductive'.
First, while there are cases of companies "stealing" an idea and giving nothing to the inventor it is uncommon (as far as I know). The reason for this is that ideas tend to be plentiful. It is the execution which is where the hard work comes in (and the risk of loss of investment).

Second, if you want to protect your idea, then you need to know what protections are appropriate for your idea. Some things are patentable and some are not. Some are patentable in some locations and some are not. So contacting an attorney in your area is a good idea (it won't be free but for a few hundred dollars you can get some advice which could make all the difference for your future. Besides patents, you might consider having everyone present in the meeting at the company sign an NDA. Keep in mind, some people refuse to sign NDAs for philosophical reasons (if you want an NDA you should bring this up well before your meeting, do not surprise anyone with it).

You might also consider checking out Law.SE but it sounds to me like you really need a one-on-one with an attorney.

Being able to find simple, innovative solutions is a great skill to have. It sounds like you do need to have the right team around you (to provide the skills you are missing) but do not sell yourself short.