Technical data

3.2 Description

The power supply unit PN 300 basically consists of two similar sources A and B that are free

of earthing, a central processor unit with interfaces for communication and a constant voltage

source of 5 V/2 A (source C).

The source A circuit is fed by the secondary winding (1) of the transformer. Here, the relay

(2) is switched over in response to the load resistance. Rectification and filtration (3) of the

voltage are the next steps. The required currents are provided at the output terminals (6) by

means of the power transistors (4) and they are measured by the resistor arrangement (5). The

internal operations are controlled by a one-chip microprocessor MCS-51 (7) the inputs and

outputs of which are galvanically decoupled by the optocoupler (8). The D/A converter (9)

provides reference voltages determined by the processor (7). These are transformed into

respective voltages and currents at the output by means of the operation amplifier (10) and the

power transistors (4). The real output parameters are tapped off via the A/D converter (11)

and are led to the processor by the optocoupler (12).

The auxiliary source (13) ensures the power supply unit for the active components.

Source B works in the same way as source A. Moreover, source B can be connected in

parallel to source A. In this case, the operation amplifier (14) takes over the control despite

the separate feedback loop of source A. The output terminals of source A (6) and B (15) are

connected in parallel by the relay contacts.

Reading of the keyboard (18) and indication on the display (17) are organized by the

processor (7). The instrument can communicate with superior systems by means of the GPIB

and

RS-232C interfaces (19).

The auxiliary source (20) handles the power supply unit of all digital circuits and of the fan

unit (21).

The parameters 5 V/2 A of source C are pre-set. The voltage is taken from the secondary

winding (22) of the transformer, it is rectified (23) and stabilized with the voltage regulator

(24). The negative pole of the output terminals (25) is grounded at the instrument mass.

The nominal operating voltage of the instrument can be set using the change-over switch for

the net voltage (26).

Operating Instructions PN 300

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