More likely, the brochure is talking about nonsense. A bipolar transistor is a sandwich consisting of three layers of doped semiconductor. Dope semiconductor has impurities in it that give the semiconductor some mobile electric charges, either positive or negative. Because it contains mobile charges, doped semiconductor conducts electricity. Because of the two depletion regions, current cannot flow from one end of the sandwich to the other.
Current begins to flow through that end of the sandwich, from the base to the emitter.
If you wire the collector so that positive charges are injected into it, current will begin to flow through the entire sandwich, from the collector to the emitter. The amount of current flowing from the collector to the emitter is proportional to the amount of current flowing from the base to the emitter. Since a small amount of current flowing from the base to the emitter controls a much larger current flowing from the collector to the emitter, the transistor allows a small current to control a large current. I cannot understand a step-up transformer. C A transformer only works with ac current because it relies on changes in a magnetic field.