Model 141A
The -12.6-volt output is adjusted by R488. Current
REGULATED Limiter, Q483, a protective circuit for the Series
UN R EG ULATEO DC OUTPUT Regulator, is normally biased off. If a short occurs
' SERIES
Dc FROM "OLTAGE- REGULATOR across the -12.6-volt output, the base of Q483 goes
RECTIFIERS
I negative by the voltage drop across R483 minus the
forward breakdown voltage of CR483, thus turning
Q483 on. The increased positive voltage on the col-
lector of Q483 is applied through Q482 to the base of
Series Regulator Q481, biasing it off. The current
which then flows through the external short is limited
DIFFER ENTI A L
AMPLIFIER to the current required to keep Q483 on. Additional
overload protection is provided by fuse F481.
-+ 4- 14. +100-VOLT SUPPLY. Differential Amplifier
REFERENCE Q443/Q444 in the +lOO-volt supply senses any varia-
VOLTAGE
141.-1-1 tion in output voltage with respect to - 100 volts. The
errorvoltage isapplied throughDriver Q442, to Series
Figure 4-2. Regulated Power Supply Block Diagram
Regulator Q441, as corrective bias. Regulation of
the output is accomplished in the same manner as in
for the supply). The driver (emitter follower or the - 100-volt supply. R453adjusts the +lOO-volt out-
amplifier) controls the bias on the series regulator, put and fuse F441 provides overload protection.
which effectively controls the series resistance. Any
4- 15. +250-VOLT SUPPLY. Sensor AmplifierQ423
change in output voltage is fed back to the series regu-
in the +2 50-volt supply sensesanyvariation in the out-
lator. The change in series resistance and the result-
put voltage, with respect to -100 volts. The error
ing voltage drop is opposite to the output voltage
voltage is amplified by DriverQ422 which applies cor-
change; thus the output voltage is maintained at a
rective bias to Series Regulator Q421. R432 adjusts
constant level.
the +250-volt output and fuse F421 provides overload
4-11. Figure 5-7 is a schematic diagram of the low protection.
voltage supply. The primary winding of transformer
4-1 6. CALI BRAT0 R.
T401 is wired through a rear panel switch for quick
conversion to either 115 or 230-vac operation. Line 4-17. The schematic diagram of the Calibrator cir-
voltage is applied to the primary of T401 through an cuit is shown in Figure 5-7. The circuit consists of
on-off switch, a fuse and a thermal switch. A pilot three parts: a tunnel diode square wave generator, a
lamp is provided to indicate when power is applied to transistor switch, and a calibration network.
T401. Two shunt resistorsare connectedto the +250-
4-18. 6. 3 volts ac is applied through R491 to tunnel
volt supply to reduce series regulator power dissi-
diode CR490, which generates a square wave at line
pation when high-current plug-ins are used The
frequency. Transistor switch Q490 is off during the
shunts are wired one to each rear panel plug and the
time of the positive half cycle of the square wave (when
internal wiring of the plug-in determines whether the
the voltage at the base is close to zero), and the col-
shunt is or is not used.
lector voltage is thus at a level set by dc voltage
4- 12. -100-VOLT SUPPLY. Since all low-voltage divider R493, R495, and R496. When the negative-
supplies are referenced to the - 100-volt supply, any going portion of the square wave is appliedto the base
change in the -100-volt supply is reflectedin the other of Q490, the transistor conducts heavily, effectively
supplies. The ac voltage from the secondary of T401 shorting the collector to ground. The output of the
is rectified by CR461-CR464 and partially filtered by Calibrator is thus zero volts. At theendof the nega-
C461, C462, and R461. The resulting dc voltage is tive input half cycle, the bias of Q490 returns to zero,
applied through Series Regulator, Q461, to the out- the transistor is switched off, and the output returns
put. Additional filter circuits are used in the plug- to its previous value.
ins. Differential Amplifier Q463/Q464 compares the
4-19. Tunnel diode bias current is supplied through
voltage across reference tube V461 with a sample of
R492. The bias current sets anoperating level for the
the output voltage, the magnitude of which is set by
diode which affects the symmetry of the square wave
theo- 100 adjust, R471. The output of the Differential
output. Cal Adj, R494 isusedto set the dc voltage at
Amplifier is applied to the base of Q462, theDriver
the collector of Q490 to - 10 volts when the transistor
Emitter Follower, which controls the bias on Series
is off. Breakdown diode CR491 reduces the output
Regulator Q461. Any tendency of the output voltage
impedance, and provides the temperature compensa-
to change, is fedbackthrough the AmplifierandDriver
tion for the circuit. Voltage divider R495/R496 re-
to the Series Regulator. The Series Regulator com-
duces the 10-volt output to 1 volt. Both lOand 1-volt
pensates for the change in outputvoltage by its change
outputs are available on the front panel of the Model
in series resistance. The -100-volt output is adjusted
14lAandthe 1-voltoutput isavailable to both plug-ins.
by R471 and fuse F461 provides overload protection
for the circuit. 4-20. HIGH-VOLTAGE SUPPLY.
4- 13. - 12.6-VOLT SUPPLY. Sensor Amplifier Q484 4-21. Figure 4-3 is ablockdiagram of the high-voltage
senses any variation of output voltage with respect to supply. The output of a regulated transistor oscil-
-100 volts and applies the error voltage to Driver lator is stepped up in voltage and applied to a series
Amplifier Q482. TheDriver increases signalcurrent of high voltage rectifiers. The positive output of the
to the level required to control Series Regulator Q481. voltage doubler is connected to the post-accelerator
4- 2 02567- 1 |
ACEC
HEWLETT-PACKARD
