Because RFL™ and Hubbell® have a policy of continuous product improvement, we reserve the right to change designs and specifications without notice.
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
L1. Inductor L1 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 L1 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 increases 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.
The 5Vdc output is unique because its level is monitored and fed back to the PWM controller. The
voltage is divided by resistors R32, R72, and R33 and fed into pin 8 of shunt regulator Q6. If the 5Vdc
output is greater than the internal reference of Q6, current is drawn into pin 1 causing optical isolator U2
to conduct. This increases the voltage applied to pin 6 of integrated circuit U1, reduces the peak current
through transformer T1, and lowers the output voltage. The negative feedback path is compensated with
resistor R64 and C22. The +15V rail is AC coupled into the regulation circuit via C14 to improve the
transient response on that rail.
To protect the 5Vdc output from excessive output currents, the voltage across shunt R26 is monitored
between pins 2 and 3 of U7. Exceeding limits, established by resistors R35 and R36, causes pin 1 to go
high and opto-isolator U3 to conduct. This causes the PWM controller to shutdown. Each of the other
outputs has short circuit protection in the form of a single transistor (Q8, Q9, or Q10) and shunt resistors
(R44, R47, or R50). A short circuit on any of these rails will also shut down the PWM controller.
Integrated circuit U6 is a series regulator, which provides post regulation for the -48V output. Post
regulation on the +15V and -15V rails is supplied to meet the voltage regulation requirements of the
supply. Q13 and its associated circuitry provides regulation for the +15V rail. Q16 and its circuitry
performs the same function for the -15V rail.
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.
M-DACS-T1 RFL Electronics Inc.
August 7, 2012 9-8 (973) 334-3100
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