drop at approximately 20 volts, leaving approximately 20 volts across the output terminals of the
Agilent Technologies supplies may use any of three basic methods of controlling the high voltage output of the Main Voltage Source: (1) the control signal from the High Voltage Control Circuit fires SCRs in the rectifier circuit to vary the dc output, (2) the control signal varies the coupling of the high voltage input transformer to adjust the ac input to the rectifiers or (3) the control signal pulse modulates the input to the rectifier to vary the dc output.
High Performance Power Supplies
Agilent Technologies manufactures several types of high performance dc power supplies with specifications at least an order of magnitude superior to the normal
Precision Voltage Sources
This line includes both CV/CC and CV/CL supplies, similar to those described previously, with a few important exceptions. The critical components of the supply, including the zener reference diode for the voltage comparison amplifier and the
Precision Constant Current Source
The concepts and circuits used in basic constant current power supplies were shown in Figure 16. This section is devoted to the refinements necessary to upgrade a basic constant current supply to a precision class, with characteristics that more closely approach an ideal current source.
An ideal current source is a current generator that has infinite internal impedance. It provides any voltage necessary to deliver a constant current to a load, regardless of the size of the load impedance. It will supply this same current to a short circuit, and in the case of an open circuit it will attempt to supply an infinite voltage (see Figure 25).
In practical current sources, neither infinite internal impedance nor infinite output voltages are possible. In fact, if the current source is to be used as a test instrument, it should have a control for limiting its maximum output voltage, so its load will be protected against the application of excessive potentials. Its output impedance should be as high as possible, of course, and should remain high with increasing frequency to limit current transients in rapidly changing load. A capacitor across the output terminals should be avoided, since it will lower the output impedance, store energy which can result in undesirable current transients, and decrease the programming speed.
One approach to the design of a current source is to add a high series resistance to an ordinary voltage source. However, it is difficult to achieve good current regulation with this design.
Typical applications for current sources call for output impedances of a few megohms to a few hundred megohms and currents of tens or hundreds of milliamperes. This means the source voltage would have to be
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