Theory of Operation
Sorensen DCS Series 3kW Supplies
5.2.1
5.2.2
5.2.3
5.2.4
5.2.5
AC Input and RFI Filter (A5 PCB)
The AC input, either single or three phase, is connected to the power supply via a four-pole
connector on the rear panel and passes through an RFI filter before going to the front panel
circuit breaker. The RFI filter serves two purposes:
•
It attenuates incoming noise on the AC input lines that could otherwise be passed
through to the load.
•
It prevents noise generated by the supply from being conducted back onto the AC
supply lines where it might interfere with the operation of other equipment connected to
that line.
AC Input Rectifier and Inrush Limiting Circuit (A6 PCB)
From the front panel circuit breaker, the AC input goes to the A6 PCB where it is rectified and
filtered to provide the raw high voltage DC supply for the main power transformer and the
auxiliary supply circuit on the A2 Control PCB. An inrush limiting circuit, consisting of a resistor
and a relay, limits the initial current to the main filter capacitor during power up.
PWM, Sync and Power Transformer Drive Circuit (A3 PCB)
The Pulse Width Modulator (PWM) circuit controls the main switching transistors through a drive
circuit and a drive transformer. The main switching transistors chop the raw, high voltage DC
supplied by the A6 PCB into a variable-duty cycle 30 kHz waveform which is applied to the
primary winding of the power transformer. Feedback signals from the A2 PCB voltage and
current control circuits and a current sense transformer which monitors the current in the
primary winding of the power transformer control the PWM output pulse width. An
optically-coupled sync signal from the A2 PCB drives a phase-locked loop which synchronizes
the switching frequency of the A3 PWM and the auxiliary supply circuit to provide noise
immunity for the PWM.
Power Transformer, Output Rectifiers, Output Filter Inductor
and Capacitors, and Local Sense Connections (Power Stage,
A7 PCB and A8 PCB)
The switching waveform applied to the primary of the power transformer by the PWM circuit
produces a square wave on the secondary windings of the transformer. The secondary
waveform is rectified and then filtered by the output inductor and capacitors to provide the DC
output. Sense connections on the A7 PCB monitor the output voltage and provide a feedback
signal to the A2 PCB voltage control circuit.
Output Current Shunt, Shunt Amplifier, and Down Programmer
(A4 PCB)
A shunt in the power supply return line is used to monitor the output current. The shunt voltage
is scaled and conditioned by a differential amplifier to provide a feedback signal to the A2 PCB
current control circuit. A down programming circuit and a preload resistor allow the supply to
5-2
Operation Manual
