Wikipedia: CNO cycle

Specifically the CNO cycle looks like this:

 12C + H --> 13N + gamma ray 

 13N --> 13C + positron + neutrino 

 13C + H --> 14N + gamma ray 

 14N + H ---> 15O + gamma ray 

 15O --> 15N + positron + neutrino 

 15N + H --> 12C + 4He 

Theoretical models show that the CNO (carbon-nitrogen-oxygen) cycle of nuclear fusion is the dominant source of energy generation in heavier stars. The cycle results in the fusion of four hydrogen nuclei (1H, protons) into a single helium nucleus (4He, alpha particle), which supplies energy to the star in accordance with Einstein's equation. Ordinary carbon serves as a catalyst in this set of reactions and is regenerated.