S p e z i a l e l e k t r o n i k G m b H
iseg Spezialelektronik GmbH
Email: [email protected]
Phone ++ 49 351 / 26 996 - 0
Bautzner Landstr. 23
http://www.iseg-hv.com
Fax
++ 49 351 / 26 996 - 21
D - 01454 Radeberg / Rossendorf
Germany
3
3. EHQ Description
The function is described at a block diagram of the EHQ. This can be found in Appendix A.
High voltage supply
A patented high efficiency resonance converter circuit, which provides a low harmonic sine voltage on the HV-
transformer, is used to generate the high voltage. The high voltage is rectified using a high speed HV-rectifier,
and the polarity is selected via a high-voltage switch. A consecutive active HV-filter damps the residual ripple and
ensures low ripple and noise values as well as the stability of the output voltage. A precision voltage divider is
integrated into the HV-filter to provide the set value of the output voltage, an additional voltage divider supplies the
measuring signal for the maximum voltage control. A precision measuring and AGC amplifier compares the actual
output voltage with the set value given by the DAC (computer control) or the potentiometer (manual control).
Signals for the control of the resonance converter and the stabilizer circuit are derived from the result of the
comparison. The two-stage layout of the control circuit results in an output voltage, stabilized with very high
precision to the set point.
Separate security circuits prevent exceeding the front-panel switch settings for the current I
max
and voltage V
max
limits. A monitoring circuit prevents malfunction caused by low supply voltage.
The internal error detection logic evaluates the corresponding error signals and the external INHIBIT signal. It
allows the detection of short overcurrent due to single flashovers in addition.
Digital control unit
A micro controller handles the internal control, evaluation and calibration functions of both channels. The actual
voltages and currents are read cyclically by an ADC with connected multiplexer and processed for display on the
4 digit LCD display. The current and voltage hardware limits are retrieved cyclically several times per second. The
reference voltage source provides a precise voltage reference for the ADC and generation of the control signals
in the manual operation mode of the unit.
The set values for the corresponding channels are generated by a 16-Bit DAC in computer controlled mode.
Filter
A special property of the unit is a tuned filtering concept, which prevents radiation of electromagnetic interference
into the unit, as well as the emittance of interference by the module. A filtering network is located next to the
connectors for the supply voltage and the converter circuits of the individual devices are also protected by filters.
The high-voltage filters are housed in individual metal enclosures to shield even minimum interference radiation.
