6
DANGER
Use extreme caution when probing
inside the 4002P power supply.
The primary circuit is exposed
in two locations
: (1) the wiring
side of the input line cord
connector block, and (2) the two
thermal switches, S1 and S2,
mounted against the heat sink.
Node
Voltage
Node
Voltage
U2 pin 8
+36.5
U6 pin 8
+9.5
3
+2.5
3
!
9.5
5
0
5
!
12.0
7
0
7
!
12.0
2
+2.5
2
!
9.5
1
+24.0
1
0
10
+23.9
10
!
0.2
6
+25.3
6
+1.4
U4 pin 8
+36.5
U8 pin 8
+9.5
3
+2.5
3
!
21.5
5
0
5
!
24.0
7
0
7
!
24.0
2
+2.5
2
!
21.5
1
+12.0
1
0
10
+11.8
10
!
0.2
6
+13.5
6
+1.3
Table 3. Typical dc Voltages
(measured with respect to TP1).
terminals, the regulator automatically converts to a
current-foldback mode. This provides power limiting
and protection of the regulator’s circuitry and
components. When excess current demands are
removed, t he regulator resumes the voltage-
regulation mode.
For convenience, only t he +24-V regulator will be
discussed. An explanation of the regulation in the
normal voltage regulation mode is given.
A 6.9-V reference voltage is set by t he precision
reference U1. This reference voltage is divided by
R3 and R4 and fed to pin 3 of the controller U2.
Simultaneously, the output is divided by R8, R9, and
R10, fed to pin 2 of U2, and compared with the
voltage at pin 3 to produce an error signal at pin 6.
Pin 6 of U2 drives the Darlington transistor, Q1, to
maintain the same volt age at pins 2 and 3. Line
regulation is improved by the zener regulator, D4,
which receives its unregulated voltage from a
voltage-doubler circuit consisting of C1, C2, D1, and
D2.
Current flow t o the output is monitored by sensing
the voltage drop ac ros s R11. When the potential
bet ween pins 10 and 1 of U2 exceeds 80 mV, the
output current and voltage will decrease, limiting the
power dissipated in Q1.
Capacitors C4, C16, and C5 tailor the frequency
response of the system to provide exc ellent
recovery time and output impedance characteristics.
D5 provides reverse-current protection for the power
supply and load in the event that a voltage source of
the wrong polarity is c onnected to the output
terminal. If loss of the sense lead should occur (pin
3 of J2), R47 provides continued operation with
some loss of regulation.
6. CALIBRATION AND MAINTENANCE
6.1. POWER SUPPLY DISASSEMBLY AND
TROUBLESHOOTING
The 4002P Power Supply needs no routine
maintenance or adjustment. If a problem develops
and trouble shooting becomes necessary, the two
module side covers should be removed to provide
access to the components.
A test point (TP1) is provided on the circuit board to
connect the reference lead of any probe. Table
shows typical dc voltages measured with respect to
ground reference potential (TP1). These voltage
levels are typical of a circuit that is operating
properly; the precise values will vary between
individual units.
6.2. DC OUTPUT VOLTAGE LEVEL
ADJUSTMENTS
Under normal conditions, no adjustment of any of
the four dc voltage levels should be required.
However, a slight readjustment could be necessary
due to component aging after a long period of use.
