A-1
APPENDIX
SERVICE INFORMATION
Figure A-1. Block Diagram
PRINCIPLES OF OPERATION
Throughout this discussion, refer to both the block diagram of Figure A-1
and the schematic diagram at the rear of the manual. The input AC line
voltage is stepped down by the power transformer and applied to the recti-
fier and filter. The rectifier-filter converts the AC input to raw DC which is
fed to the positive output terminal via parallel series regulator(Q1 and Q3)
and current sampling resistor(R2). The regulator, part of the feedback loop,
is made to alter its conduction to maintain a constant output voltage or cur-
rent. The voltage developed across the current sampling resistor is the
input to the constant current error amplifier. The constant voltage error
amplifier obtains its input by sampling the output voltage of the supply.
Any changes in output voltage or current are detected, amplified by the
error amplifier and driver and applied to the series regulator in the correct
phase and amplitude to counteract the change in output voltage or current.
Two error amplifiers are included in a CV/CC supply, one for control-
ling output voltage, the other for controlling output current. Since the
constant voltage amplifier tends to achieve zero output impedance
and alters the output current whenever the load resistance changes,
while the constant current amplifier causes the output impedance to
be infinite and changes the output voltage in response to any load
resistance change, it is obvious that the two amplifiers can not oper-
ate simultaneously. For any given value of load resistance, the power
supply must act either as a constant voltage source or as a constant
current source - it can not be both; transfer between these two modes
is accomplished at a value of load resistance equal to the ratio of the
output voltage control setting to the output current control setting.
The reference and bias circuit provides stable reference voltages which
are used by the constant voltage/current error amplifier circuits for compar-
ison purpose. The digital meter circuit provides an indication of output volt-
age and current for constant voltage or constant current operating modes.
The display power circuit provides voltage which is used by A/D con-
verter and LED drive.
Diode CR3 is connected across the output terminals in reverse polar-
ity. It protects the output electrolytic capacitor and the series regulator
transistor from the effects of s reverse voltage applied across the out-
put terminals.
PERFORMANCE TEST
The following provides the test procedure in high current range for verifying
the unit's compliance with the specifications and characteristics of Table in
page 1-3. The same test procedure may be applied to low current range.
Test Equipment Required
The following Table lists the equipment required to perform the tests
and adjustments. You can separately identify the equipment for per-
formance tests, or calibration in the USE column of the Table.
Summary of Contents for E361 A Series
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