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Sorensen DCS Series 3kW Supplies
Theory of Operation
Output Voltage and Current Readback Circuits
These circuits provide calibrated, switch-selectable 0-5V or 0-10V analog readback signals for
remote monitoring of the output voltage and current. The output voltage readback signal is
available at pin 19 of the rear panel J3 connector and the current readback signal is available at
pin 7.
The
voltage readback circuit
is made up of op amp U6, switch SW1-4, calibration pots R55
and R56, and resistors R52, R53, R54, and R57. The op amp monitors the output voltage of the
supply through the positive sense divider formed by resistors R6, R7, R44, and R43. For 0-5V
readback, switch SW1-4 is CLOSED and resistors R53, R54, R57, and trimpot R56 scale and
calibrate the monitor signal. Trimpot R55 is use to null any output offset. For a 0-10V readback
signal, switch SW1-4 is OPEN, removing resistor R53 from the scaling resistors.
Operation of the
current readback circuit
is the same as the voltage readback circuit. The
circuit is made up of op amp U2, switch SW1-3, calibration pots R23 and R24, and resistors
R19, R20, R21, and R25. The input to the op amp is from the current shunt amplifier through the
divider formed by resistors R22 and R26.
Fan Control and Over-temperature Shutdown Circuit
The
fan control circuit
monitors the temperature of the A6 PCB input rectifier heatsink, the
A3 PWM heatsink, and the output rectifier heatsink, using thermal sensors RT1, RT2, and RT3
respectively. Op amp U7-B monitors the average value of the thermal sensor inputs (0.595 Vdc
@ 25 degrees C) at pin 5 and controls the fan voltage through op amp U7-C and MOSFET Q3.
As the temperature of the heatsinks rises, the voltage at pin 5 falls due to the negative
temperature coefficient of the thermal sensors and the output of U7-B drops. This causes the
output of U7-C to rise, drawing more current through Q3 and increasing the fan speed.
When the heatsink temperature reaches approximately 100 degrees C, the output of U7-B goes
negative, causing the output of U7-D to go high. This activates the
internal shutdown
circuit
and the PWM shutdown lines through diodes CR16 and CR15. The front panel OTP
(over-temperature protection)
LED is illuminated through resistor R28. The J3 remote monitor
line is fed by resistor R18. The IEEE-488 monitor line is activated through pin 5 of connector P2.
Operation Manual
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