Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
The 5Vdc output is unique because its level is monitored across diode CR6, resistors R42 and R43, and
potentiometer R44. The wiper arm of potentiometer R44 is fed to pin 6 of dual error amplifier U3 and is
compared against an internal reference set at pin 7 of U3. If the 5Vdc output is greater than the
reference, pin 14 of U3 goes high causing optical isolator U2 to conduct. This reduces the voltage
applied to pin 5 of integrated circuit U1, reduces the peak current through transformer T1, and lowers
the output voltage. The negative feedback path is compensated with resistor R41 and C44.
To protect the 5Vdc output from excessive output currents, the voltage across shunt R26 is monitored
between pins 2 and 3 of U3. Like the voltage feedback path, exceeding limits, established by resistors
R35 and R36, causes pin 14 to go high and reduces the output voltage.
Integrated circuits U6, U7, and U8 are series regulators, which provide post regulation for the secondary
outputs. Post regulation is required to meet the voltage regulation requirements of the supply. Feedback
for regulator U7 is provided by resistors R47, R25, potentiometer R49, and CR16. Feedback paths for
the other regulators are similarly structured.
All outputs have or’ing diodes. These diodes; CR12, CR15, CR18, CR19, allow two supplies to be
connected in parallel. Feedback signals for all outputs are taken before the or’ing diodes. The
temperature voltage sensitivities introduced by the or’ing diodes are compensated with diodes CR13,
CR16, CR17, and CR6.
9.2.5 THEORY OF OPERATION (9547-965, -975)
The RFL IMUX 2000, 75 Watt power supply is a multiple output, forward, dc to dc converter. The
9547-975 power supply operates from a 19 to 29 Vdc input and the 9547-965 power supply operates
from a 38 to 150 Vdc input. Each of these supplies has four outputs: 5 Vdc at 6.0 Adc, + 15 Vdc at 1.75
Adc, -15 Vdc at -1.0 Adc, and -48 Vdc at 100 mAdc. All of the outputs are connected to a common
ground. The 5 Vdc output is constantly monitored and signals are provided if the output should exceed
lower limits. All outputs contain or’ing diodes for paralleling a second supply for redundancy.
Input power is fed through terminals A23-25. C23-25 and A30-32, C30-32. An external alarm and
interface board provides fusing and EMI suppression.
Diode CR1 protects the power supply from reversal of input voltage. Under such conditions, a fuse on
the alarm and interface board clears. Inrush limiter TH1 allows charging of capacitor C5 from a stiff ac
or dc source, as applicable, without excessive input currents.
The forward converter is designed around PWM integrated circuit U1. The device has an internal clock
set by resistor R12 and capacitor C11/C52. Power for the device is initially provided by a series
regulator consisting of MOSFET Q3, resistors R2 and R8, and diode CR5. With power applied and
internal clock set, pin 11 of U1 goes high causing MOSFETs Q1, Q2, and Q5 to conduct. This causes
the dc bus voltage to be applied across windings 1 and 2 of transformer T1 and conduction of output
diodes CR7, CR9, CR11, and CR14. Upon conduction of these diodes, power flows from the input to
the output of the power supply. The dc bus current, which flows through MOSFETs Q1 and Q2 is
detected across resistors R5, R6, R98, and R99 and is monitored at pin 4 of U1. When the peak
increases to a level set at pin 7 of U1, pin 11 of U1 is set low causing transistor Q4 to conduct.
M-DACS-T1 RFL Electronics Inc.
August 7, 2012 9-7 (973) 334-3100
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