Service Information - HP E3610A Operating And Service Manual

APPENDIX
SERVICE INFORMATION
AC
NPUT
XFMR
DISPUY
POWER SUPPLY
• • + 5 V
• G N D
CVrtX h»cv
INDICATOR
ORCUIT U - C C
REFERENCE ANO
BIASSIPPLY
+12 V
+ 5 V
— CREF
-12 V
RECTinEfl
FILTER
SERIES
REGULATOR
Ofl
GATE
+«V —
GND -
CURRENT
OISPWY
CIRCUIT
VOLTAGE
DISPLAY
CIRCUIT
CONSTANT
CURRBtT
ERROR AMP
. ^ V S ^
CREFO-
CCSET
ORCUIT
u
CONSTANT
VOLTAGE
ERROR AMP
DRIVER
METER
INPUT
ORCurr
DC
OUTPUT
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 rectifier 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 resis-
tor(R2). The regulator, part of the feedback loop, is made to alter its
conduction to maintain a constant output voltage or current. 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
controlling 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 resis-
tance 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 operate 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 comparison purpose. The digital meter circuit provides an
indication of output voltage and current for constant voltage or
constant current operating modes.
The display power circuit provides voltage which is used by A/D
converter and LED drive.
Diode CR3 is connected across the output terminals in reverse
polarity. It protects the output electrolytic capacitor and the series
regulator transistor from the effects of a reverse voltage applied
across the output terminals.
PERFORMANCE TEST
The following provides the test procedure in high currant range for
verifying the unit's compliance with the specifications and character-
istics 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
performance tests, or calibration in the USE column of the Table.
A-1