Fluke 5220A, Instruction Manual

Page: 29 / 138

3-1
Section 3
Theory of Operation
3-1. Introduction
This section of the manual contains an overall functional description followed by a
detailed circuit analysis of the 5220A. Both descriptions are supported by block
diagrams. Component level descriptions contained in the circuit analysis are referenced to
the detailed schematics in Section 8 of this manual.
3-2. Overall Functional Description
3-3. General
The 5220A is a transconductance amplifier. That is, a current source whose output
current is proportional to an analog input voltage. Electrically viewed at the output
terminals, the 5220A appears as a current source with an output impedance that is very
much greater than the load resistance. Its input terminals exhibit a similar characteristic;
the input impedance is larger than that of the input voltage source.
Functionally, the 5220A, as shown in Figure 3-1, can be divided into two sections, analog
and digital. The analog section consists of the power supplies, the transconductance
amplifier, and associated analog control circuitry. The digital section comprises the logic
necessary for overall control, and the interfaces necessary for front panel (local)
operation and remote operation by way of the Fluke MIS Bus.
3-4. Analog Section
The power supply used in the 5220A provides operating voltages for both the analog and
the digital section of the unit. It consists of three separate assemblies: the A2 Transformer
Assembly, the A3 Cap Bus, and the A4 Regulator. The Cap Bus and Regulator
Assemblies comprise the output portion of the supply, while the Transformer Assembly
provides isolated ac power for the power supplies. Regulated supply voltages are a
function of the A4 Regulator. These i5 V dc and +5 V dc Isolated for the digital
circuits and +15/-15 V dc for analog circuit operation. Unregulated voltages are a
function of the A3 Cap Bus. The Cap Bus is a high-current, +12/-12 V dc source for the
5220A current output.