I've made a boost converter circuit, with a MOSFET as a switch, and a (7)555 timer operating as an astable oscillator, and it's output goes directly to the MOSFETs gate pin. The problem is that the input voltage for the boost converter is unstable (solar panels). When the input from the solar panels is high the output from the boost converter is also higher and when input's low, the output is also lower. That is because the 555 is operating at a constant frequency and duty cycle.
What can you suggest for controlling the 555, so its output would switch the MOSFET at such frequency/duty cycle, so that the output voltage of the boost converter would be stable? I need it to be around 14.7V, minimum 14.4V and maximum 15V for my CSB GP 12120 battery.
I've played around with 555's control voltage (5) pin, tried to use op amp to compare the batteries voltage to the solar panels voltage and apply the result to the 555 in a couple of ways (the fifth pin and the supply voltage). There were cases, where the output was more stable, but still, that was not even close to what I need. Maybe I just didn't do it right, or maybe 555 is just not what I need.
So in case you think I should use something else than a 555 timer, please suggest it. And please give me as many details as possible.