Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
9.2.4 THEORY OF OPERATION (9547-930)
The RFL IMUX 2000 M-DACS, 50 Watt power supply is a multiple output, forward, dc to dc converter.
The 9547-30 power supply operates from180 to 265 Vac input. The supply has four outputs: 5 Vdc at
4.5 Adc, + 15 Vdc at 1.0 Adc, -15 Vdc at -0.75 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 form 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. 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 and R6 and is monitored at pins 3 and 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. This drives MOSFETs Q1 and Q2 to
an off state. Transformer T1 voltage reverses and diodes CR8, CR9 (opposite device), CR10, CR14
(opposite device) conduct and circulate current stored in inductor L3. Inductor L3 and capacitors C19,
C24, C26, and C34 form a low pass filter producing a dc that is the half cycle average voltage produced
by transformer T1. Inductor L3 is a multi-winding inductor that is matched to transformer T1.
The auxiliary winding of transformer T1, terminals 5 and 6, provides a source of power for the supply’s
control circuit. After the first few cycles, the voltage at capacitor C17 increase rendering MOSFET Q3
non-conductive.
The secondary auxiliary winding of transformer T1, terminals 3 and 4, capacitor C6, and diode CR2, is a
clamp to limit voltage transients across MOSFETs Q1 and Q2.
M-DACS-T1 RFL Electronics Inc.
August 7, 2012 9-6 (973) 334-3100
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