SPELLMAN HIGH VOLTAGE
Introduction 1
Installation and Operating Manual
Page1-7
118149-001 REV F
1.3
THEORY OF OPERATION
1.3.1
Function Overview
The XRB011 MONOBLOCK Series is a complete integrated system consisting of a high voltage power
supply (HVPS), filament supply, X-ray tube and oil encapsulant which provide the required high voltage
insulation in one compact enclosure. The combination of proprietary control system and protection circuitry
enables the supplies to operate under arcing and extreme transient conditions without damage or interruptions.
Additional advantages are the elimination of high voltage cables and extremely low leakage X-ray radiation.
The XRB011 MONOBLOCK Series incorporates local and remote programming, monitoring, and fault
indicators including safety interlock. The X-ray source is a sealed unit containing a HVPS and an X-ray tube.
The insulating oil provides electrical insulation for the high voltage sections of the power supply and the X-ray
tube in a sealed tank. The oil also functions as a coolant to carry heat away from the tube. Convection cooling
augmented by customer provided minimum 50cfm external fan is required for the 50W option. A rubber
bellows in the tank of the X-ray source compensates for the expansion of the oil as the oil temperature varies
with operating conditions thereby eliminating the need for bulky overflow tank.
The XRB011 MONOBLOCK is basically a DC to DC power converter. Within the generator, conversions of DC
to DC, then to high frequency AC, then to high voltage DC take place. By reviewing further the sub-
assemblies, a basic understanding of the process can be gained.
1.3.2
Input Line Power
The Input DC voltage provides the voltage for the high voltage inverter and the filament supply.
The line input voltage can vary from 23V up to 25V within the series.
1.3.3
HV Inverter
The inverter is a “Push-Pull” topology. Voltage mode control is used for driving the inverter. Two MOSFET
transistors are used as switches in the HV inverter. These MOSFET provide high frequency switching to
control the primary current flow in the high voltage transformer.
Circuits on the Control board provide the gate control of the switches. The PWM IC generates gate drive
control signals.
1.3.4
High Voltage Transformer
The output of the High Frequency Quasi-resonant Inverter is connected to the primary of the High Voltage
Transformer. The High Voltage Transformer is a step up type. Typical secondary voltage is in the range of
5.7kV depending upon output voltage ratings.
1.3.5
High Voltage Assembly
The High Voltage Assembly circuitry typically consists of two high voltage multipliers to generate ±40kV. The
high voltage section is a bipolar ground-referenced supply. The multiplier is a standard diode-capacitor
multiplier with seven stages of voltage multiplication and the divider is a precision resistance divider string.
Each supply is capable of generating 40 kV.
A high bandwidth resistive/capacitive divider provides voltage feedback for regulation and monitoring. A sense
resistor connected at the low voltage end of the High Voltage Rectifier provides current feedback for regulation
and monitoring.
1.3.6
System Control PWB
Control of the generator utilizes sophisticated analog and digital circuitry resulting in fast and accurate control,
protection and signaling to the user.
This generator is based on advanced PWM control utilizing the specific integrated circuit. Analog signals are
digitized in A/D converter and processed within DSP circuits to provide maximum accuracy and reliability.
All feedback signals are sent to the user interface through digital and D/A circuits where switching is possible
between feedback and program signals. This allows the user to preset the desired output before energizing
high voltage.
All program voltages are typically ramped up to set level by the digital ramp generator.
