Agilent Technologies 90B manual Constant Current Power Supply

Figure 16. Constant Current Power Supply

CONSTANT VOLTAGE/CONSTANT CURRENT (CV/CC) POWER SUPPLY

Because of its convenience, versatility, and inherent protection features, many Agilent supplies employ the CV/CC circuit technique shown in Figure 17. Notice that only low power level circuitry has been added to a constant voltage supply to make it serve as a dual-purpose source.

Two comparison amplifiers are included in a CV/CC supply for controlling output voltage and current. The constant voltage amplifier approaches zero output impedance by varying the output current whenever the load resistance changes, while the constant current amplifier approaches infinite output impedance by varying the output voltage in response to any load resistance change. It is obvious that the two comparison amplifiers cannot operate simultaneously. For any given value of load resistance, the power supply must act either as a constant voltage or a constant current supply--it cannot be both. Transfer between these two modes is accomplished automatically by suitable decoupling circuitry at a value of load resistance equal to the ratio of the output voltage control setting to the output current control setting.

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