HP 5300A - Power Supply; Power Input Section; Overvoltage Fail-Safe Circuit

Model
5300A
;
Theory
of
Operation
4-54. A standard parallel output for use with digital
recorders such as the HP 5055A or HP 5050B may be
obtained with a recorder interface accessory, HP
Model 10533A. This accessory provides the serial]-to-
parallel conversion and includes 6-feet of cable to
connect between the 5300A and the digital recorder.
4-55. POWER SUPPLY
4-56. The power supply is a small, high efficiency
power converter capable of supplying the necessary
output voltages for the analog circuits, Light-
Emitting-Diode (LED) Display, and digital circuits
(see Figure 4-11). The unit will operate from 115 Vac
or 230 Vac, 50 to 400 Hz or from an accessory battery
pack, such as the HP 5310A, which has nominal out-
put voltage of 12 V. The power supply consists of
three basic sections, which are each described in sub-
sequent paragraphs:
a. Power Input Section. Consists of input trans-
former T1 and bridge rectifiers AlCR1, CR2, CR3,
CR4. This section converts ac input power to rectified
dc.
b. Overvoltage Fail-Safe Circuit. Consists of
A2Q4, Q6, Q8, Q9, and associated components. Shuts
the power supply off if a component fails and causes
excessively high output voltages.
c. Dec-to-Dc Converter. Consists of the remain-
ing power supply components and operates frora a dc
voltage of 10 V to 30 V; provides +17 Vdc, +5 Vdc, and
+3.5 Vdc output. The dc input voltage is from the
rectified dc supplied by Tl or from the accessory
battery pack (when used).
4-57. Power Input Section
4-58. Input power, 115 Vac or 230 Vac, is stepped
down by T1 and rectified by bridge rectifiers A1CR1
to AiCR4. Capacitor A1C6 protects these rectifiers
from high voltage transients in Tl and A1R14 pre-
vents A1C6 from charging to an excessively high volt-
age. The dc output voltage from the bridge rectifiers
is nominally +22 volts, when fully loaded by the main-
frame dc-to-de converter and the battery pack under
CHARGE conditions.
4-59. Overvoltage Fail-Safe Circuit
4-60. If the +5 V supply increases to more than +5.8 V,
emitter-to-collector current flows through A2Q4 and
charges capacitor A2C3. For short transient over-
voltages, A2C3 does not charge enough to activate
A2Q6. For continuous overvoltages A2C3 continues
to charge and current is coupled through A2CR3 into
the gate element of SCR A2Q6. This causes A2Q6 to
Figure 4-11. 5300A Power Supply Block Diagram
t 4
50
SWITCH
+22V0C
CRI-4
BRIDGE
RECTIFIER
04,6,8,9
ee | FILTER 7 4.6.8
CURRENT VOL TAGE
RI,RU,CS
RIPPLE
CANCEL
NE T WORK FEEDBACK
FAIL- SAFE
CIRCUIT
TRANSFORMER’
Q2.3
DIFFERENTIAL
CURRENT
SOURCE
A2Q01,5,7
CONTROL
TURN OFF
FOR AiQ3
H.W.
RECTIFIER
AND
FILTERS
Sw
TRANSISTOR