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Circuit Description
POWER SUPPLY BOARD
CAUTION: Dangerous voltages are present
on this circuit board whenever the instru-
ment is attached to an AC power source,
whether or not the front panel power
switch is "on". The front panel power
switch only enables the voltage regulators
in the unit, but the unregulated voltages
are always present.
Always disconnect the power cord and
wait at least two minutes before opening
the unit. Check the LED at the front edge
of the power supply board. The unit is safe
only if the LED is OFF. If the LED is ON,
then DO NOT attempt any service on the
unit.
UNREGULATED POWER SUPPLIES
A power entry module, with RF line filter, is used
to configure the unit for 100, 120, 220, or 240
VAC. The line filter reduces noise from the instru-
ment and reduces the unit's susceptibility to line
voltage noise. R1 is an inrush limiter to limit the
turn on current and TS1 is a thermal switch which
will interrupt the AC line if the heat sink tempera-
ture rises to 50°C.
Bridge rectifiers are used to provide unregulated
DC at ±22V, ±18V, ±8V, and -4V. Schottky diodes
are used for all supplies except the ±22V in order
to reduce rectifier losses.
The comparator, U2C, provides a square wave
line crossing signal.
Resistors provide a bleed current on all of the un-
regulated supply filter capacitors. Because of the
large capacitances in this circuit, the time for the
voltages to bleed to zero is about a minute after
the power cord is removed.
Note that the AC power source must be re-
moved in order to discharge the unregulated
supplies.
POWER SUPPLY REGULATORS
The voltage regulators provide outputs at +5V, -
5.2V, -2V, ±15V, and ±12V. The low voltage regu-
lators (±5V and -2V) are designed to operate with
a very low drop-out voltage.
U9 is a precision 5.00V reference which is used to
set all of the output voltages. This provides very
accurate power supply outputs. The power switch
simply switches the power to U9. When U9 is off,
the reference voltage is removed and the regula-
tors drop to zero volts.
There are 2 +5V supplies, one to power the CPU
board and disk drive (+5V_P), and one to power
the ECL and TTL data acquisition boards (+5V_I).
The following description refers to the +5V_P sup-
ply but describes the +5V_I, -5.2V, and -2V sup-
plies as well.
The main pass transistor is Q3. The base of this
transistor is controlled so that the emitter will pro-
vide a low impedance source of 5 VDC. The cur-
rent gain of Q3 remains large until the collector-
emitter voltage drops to about 0.4 VDC, hence the
low drop-out voltage of the regulator. The base of
Q3 is driven by the emitter of Q6 which is driven
by the output of the op amp, U3B. By comparing
the output of the regulator to the 5.00V reference,
the op amp maintains the regulator's output at
5.00 VDC. The current output from the regulator is
measured by the 0.1Ω resistance of fuse F1. If the
current exceeds about 2 Amps, then the output of
U3A turns on, pulling the sense input of U3B high,
thereby turning off the regulator's output.
U7 and U11 are regulators for ±15 VDC. U8 sens-
es the output voltages and compares them to the
reference to control the adjust pin of the regula-
tors.
U13 and U15 are the ±12V regulators. Since these
supplies do not need to be accurate, output sens-
ing is not used, instead, the ±15V outputs are
used to set the output levels.
U10 and U12 provide unswitched ±15V sources.
These voltages are on whenever the unit is
plugged into an AC power source.
U2 provides power-up reset and U1A provides
power down reset.
The 24 VDC brushless fan speed is controlled by
the temperature in the box. The warmer the box,
the faster the fan turns. When cool, the 10 mA
drawn by R5 through R4 is not sufficient to turn on
Q2. As the box warms above 40°C, R4 becomes a
high resistance and some of the 10 mA will go into
the base of Q2 turning speeding up the fan. Diode
D13 keeps the fan at half speed even when cool.
The proportional temperature control can double
the fan speed if necessary.
Содержание SR430
Страница 2: ......
Страница 6: ...4 ...
Страница 22: ...20 Guide To Operation ...
Страница 26: ...24 Guide To Operation ...
Страница 36: ...34 Mode Menu ...
Страница 54: ...52 Save Menu ...
Страница 60: ...58 Recall Menu ...
Страница 70: ...68 Plot Menu ...
Страница 74: ...72 Test Menu ...
Страница 76: ...74 Info Menu ...
Страница 97: ...96 Remote Programming ...
Страница 99: ...98 98 Program Examples ...
Страница 107: ...106 106 Test and Calibration ...
Страница 113: ...112 112 Using Photomultiplier Tubes ...
Страница 125: ...124 124 124 Circuit Description ...