Transistor output stage current stabilising arrangement - uses constant current transistor, diode and resistance circuit supplying coupled output transistors

摘要

A control circuit provides current stabilisation of a final transistor stage, such as may be used to drive loudspeakers, against changes in supply voltage. The output stage consists of two transistors that are coupled together with two other transistors to operate as quasi-complementary final stages. Four resistors provide adjustment of the operating point, and the load is coupled over a capacitance. A constant current supply for the output stages is provided by a transistor, a variable resistance, diodes and a resistor. Another resistor allows the current to be adjusted so that constant current flows up to a limitting value fixed by a bootstrap resistor and a limiting resistor.