Figure 26. Impedances Shunting the Load Degrade Current Regulation
As shown in Figure 27, the CCB design includes three key sections which determine its unique regulating pro-
The Programming/Guard Amplifier is an independent, variable constant voltage source, whose output voltage EG is linearly dependent upon the setting of RQ, being equal to ESRQ/RS. The guard aspects of this circuit are discussed in detail later; it is sufficient to note here that this circuit permits linear output current control while facilitating the common point connection at the inboard side of the current monitoring resistor.
The Programming/Guard Amplifier provides the programming voltage EG for the Main Current Regulator; this dc voltage, which is negative with respect to circuit common, is applied to one of the inputs of the differential Current Comparison Amplifier. The other input of this differential amplifier is connected to the current monitoring resistor RM. The Current Comparison Amplifier continuously compares the voltage drop across the current monitoring resistor (IORM) with the programming voltage (EG). If these voltages are momentarily unequal due to a load disturbance or a change in the output current control setting, this error voltage is amplified and applied to the series regulator transistors, altering the current conducted through them and forcing the voltage drop IORM to once again equal EG.
The output current is related to the programming voltage and reference voltage by the relationship
IO = | EG | = | ES | • | RQ | |
RM | RM | RS | ||||
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As this equation suggests, RM is a critical component and is selected to have low noise, low temperature coef- ficient, and low inductance.
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