مدل سازی، تجزیه و تحلیل و پیاده سازی بارهای مقاومتی تغذیه مبدل فلای بک کم قدرت ولتاژ بالا Modeling, Analysis and Implementation of High Voltage Low Power Flyback Converter Feeding Resistive Loads

I. INTRODUCTION High Voltage Power Supply encompass a broad application spectra such as analytical instruments for spectroscopy and electrophoresis, ion mass analyzers, smart material based actuators etc [1]–[4]. Analytical instruments like ion mass analyzer perform study and characterization of ions for space instrumentation systems. Such instruments comprise of electrostatic ion detector and deflector plates. The ion detector requires voltage in the range of 1.5 – 3 kV to scan and focus ions of specific energy level and is electrically modeled as a resistive load of 20 – 50 MΩ [2]. Analytical instrument employed in ozone generation require voltage in the range of 1 – 3 kV and is electrically modeled as resistive load (375 – 700 kΩ) [3]. Such devices are battery fed, operates with low power (typically in the range of 200 mW – 5 W) and need light weight high power density intermediate processing systems. A constant regulated output voltage with lower steady state ripple is required for effective operation of instruments modeled as resistive loads. To cater such requirements, numerous topologies each with distinct advantages and disadvantages are proposed in literature [5]. Flyback converters have been widely used because of their relative simplicity and their performance for power rating less than 100 W [6]. Some constructive features of the flyback converter include: isolation between the source and load side, requires a capacitive filter on the HV side, compact with low component count. Transfer of energy from source to load in a flyback converter occurs by energy storage in an intermediate flyback transformer. In HVLP flyback converters for the above applications feeding resistive loads, flyback transformers are designed with larger secondary turns and hence leads to higher self capacitance of transformer winding [7]–[9]. In general, the presence of parasitics impose a deviating behaviour in converter’s operation, in comparison with the ideal characteristic. In a flyback converter specific to HVLP applications, the primary requirement of achieving the desired steady state gain is itself restricted by the parasitic capacitances [10]. A significant energy exchange occurs between parasitic capacitance (Cef f ) and magnetising inductance (Lm) resulting in notable transition intervals apart from the typical intervals of an ideal flyback converter [11]. Converter’s operation is categorized as Continuous (CCM) or Discontinuous (DCM) based on the variations of the load. CCM operation is also known as incomplete energy transfer mode since a part of the energy drawn from the source is retained by the flyback transformer. CCM for flyback converters specific to HVLP applications poses semiconductors with higher voltage stress and results in an inefficient hard switching process. The presence of a high turns ratio transformer results in high effective capacitance (Cef f ) across drain to source of the primary active switch; this results in a significant amount of energy loss at the turn on instant of the active switch. Therefore the switching loss of the converter dominate the conduction loss.