Agilent Technologies E3620A Operating And Service Manual page 76

PRINCIPLES OF OPERATION
(Block Diagram Overview)
This section presents the principles of operation for the
E3620A Dual Output Power Supply. Throughout this discus-
sion, refer to both the block diagram of Figure A-1 and the
schematic of Figure A-10 and Figure A-11.
The E3620A contains two independent power supplies (des-
ignated V1 and V2), a common input power circuit, and a
meter circuit that can monitor the output voltage and current
of either supply.
The two primary windings of the power transformer are con-
nected in one of three different ways by setting the two slide
switches mounted on the circuit board. These switches select
one of the nominal ac input voltages for which the supply is
designed: 100 V, 115 V, or 230 V. The transformer secondar-
ies, together with rectifiers and capacitor filters, provide raw
dc for two output regulator circuits, for two reference and bias
SERVICE INFORMATION
Figure A-1. Block Diagram
supplies and for a display power supply.
By comparing its output to a high-stability reference, the V1
supply's 0 to 25 V regulator holds its output voltage at the
value determined by the V1 VOLTAGE control of the front
panel. Any error in the actual output as compared to the
desired output is amplified by an operational amplifier and
applied as feedback to control the conduction of a series reg-
ulator transistor. As a result, the voltage across the series
transistor varies so as to hold the output voltage constant at
the desired level. The high gain of the voltage comparison
amplifier and the stability of the reference voltage ensure that
input voltage or load current variations have little effect on the
output voltage. The V1 output is protected by a fixed current
limit at minimum 105% of its 1 amp maximum rated output.
A-1