Controlled current source - is adjusted by selecting specified values for transistors, emitter resistor and base voltage divider

摘要

The current source comprises a transistor with a resistive voltage divider connected to its base and an emitter resistor connected to its emitter. A controlling signal voltage is applied to its base. The collector current provides the modulating signal for an amplitude modulator. The current source is adjusted by setting the emitter resistor with precision to a specified value related to the max. controlling signal voltage, the d.c. collector current and the degree of modulation of the modulating signal. The division is set so that in the absence of a controlling signal voltage it is equal to the voltage drop across the emitter resistor or to the current through this resistor.