The internal circuit diagram of the GY-CD type charger clearly shows that the entire circuit consists of four parts: differential input stage, voltage gain stage, complementary output stage, and constant current source circuit. The input stage is composed of transistors Ti to T. The T1 to T4 form a combination of common collector (cc) and common base (CB) differential circuit, with T9 being a lateral PNP arm. The main advantage of this structure is its high differential and common mode input voltages. The voltage can reach up to 30V, with a Vcc voltage of 12V. T5 is a mirror current source with a buffer stage, serving as the active load for this stage and also providing unipolarization functionality. N provides a constant collector current for T.
