Downhole logging in oil and gas wells serves as a core link in oil and gas exploration and development. By lowering logging tools thousands of meters deep into oil and gas wells, it measures key formation parameters in real time, including lithology, porosity, permeability, oil and gas saturation, and well trajectory, providing accurate data support for hydrocarbon discovery, reserve evaluation, and development planning. The high‑voltage power supply is an essential power component of downhole logging tools. It delivers stable high‑voltage bias and power drive to detectors, signal amplification circuits, transmitting circuits and actuators of various logging instruments such as natural gamma ray logging tools, density logging tools, neutron logging tools, acoustic logging tools, imaging logging tools, and formation testers. It converts bus power from downhole tools into high‑voltage DC power required by logging sensors. Its operational stability at high temperatures, startup capability, parameter accuracy, miniaturization integration, and vibration and shock resistance directly determine the measurement accuracy, operating depth and continuous working time of logging tools, as well as the efficiency and success of overall oil and gas exploration and development operations. Downhole logging scenarios impose extreme technical requirements and core challenges on high‑voltage power supplies that differ greatly from conventional industrial power supplies. First, long‑term stable operation under ultra‑high temperatures. Downhole temperature rises with well depth, reaching 125℃~150℃ in ordinary wells, 175℃~200℃ in deep and ultra‑deep wells, and exceeding 220℃ in some ultra‑high‑temperature geothermal and deep hydrocarbon wells. Conventional electronic components suffer severe performance degradation above 125℃, including sharp increases in semiconductor leakage current, threshold voltage drift, rising on‑resistance, thermal runaway and permanent failure; capacitance attenuation and excessive leakage; dramatic drop in magnetic core permeability with higher losses; and softening, accelerated aging and degraded insulation of insulating materials. The power supply must operate continuously and stably at 175℃, while ultra‑high‑temperature models must function normally at 225℃, with output voltage drift below ±1% across the full temperature range and no irreversible performance degradation or thermal runaway. Second, extreme miniaturization and high power density. Wellbore diameters generally range from 4.5 inches to 12 inches, and outer diameters of common logging tools are merely tens of millimeters, typically between 30 mm and 100 mm. Internal installation space is extremely narrow with a slender cylindrical shape, imposing strict limits on power supply diameter, length and volume. The outer diameter is usually required not to exceed 50 mm, length within 300 mm, power density ≥100 W/in³, while maintaining light weight. Traditional high‑voltage power supplies are bulky and structurally dispersed, making them incompatible with narrow cylindrical downhole layouts. Third, strong vibration, shock resistance and adaptability to harsh downhole environments. During run‑in and pulling operations, logging tools endure continuous severe vibration and shock with acceleration up to hundreds of g. Downhole environments feature high pressure, high humidity, and corrosive gases such as hydrogen sulfide and methane, together with drilling fluid erosion. Downhole pressure in ultra‑deep wells exceeds 100 MPa. The power supply must deliver excellent vibration and shock resistance, high pressure tolerance and corrosion resistance for stable operation under severe downhole conditions. Fourth, wide input voltage range and high efficiency. Logging tools are powered from the surface through multi‑kilometer logging cables with large line resistance causing severe voltage drop. Meanwhile, surface supply voltage and downhole loads fluctuate significantly. The power supply must support an input range covering 50%~150% of the nominal voltage, enabling normal startup and operation at low input voltage, with overall conversion efficiency ≥85% to minimize power consumption, cable loss and internal heating, preventing further temperature rise inside tools. Fifth, ultra‑low electromagnetic interference and high output stability. Logging instruments capture weak formation signals at the nanovolt to microvolt level and are highly sensitive to electromagnetic noise. Switching noise and electromagnetic radiation from high‑voltage power supplies may couple into signal acquisition circuits via radiation or conduction, causing signal distortion, reduced signal‑to‑noise ratio, lower accuracy and even failure to identify valid formation signals. The power supply must achieve extremely low conducted and radiated interference, with output stability better than ±0.5% and peak‑to‑peak output ripple below 0.1%. Sixth, high reliability and long service life. Logging operations entail extremely high costs of hundreds of thousands of RMB per run. Unexpected shutdowns or equipment failures interrupt logging and result in heavy economic losses. Since on‑site maintenance is impossible downhole, the power supply must feature an MTBF ≥1×10⁴ hours and a design life ≥5 years, together with comprehensive protection functions to cope with complex downhole operating conditions. Seventh, fast dynamic response and load adaptability. Loads change rapidly and drastically under different measurement modes, with step variations from no load to full load within hundreds of microseconds. The power supply must deliver ultra‑fast dynamic response, with output voltage fluctuation below ±2% and settling time<100 μs during load steps, adapting to wide load variations across measurement modes. Targeting the core operating requirements and technical challenges of high‑voltage power supplies for downhole logging tools in oil and gas wells, this methodology establishes a comprehensive technical framework covering high‑temperature adaptive topology design, full‑range temperature performance optimization, miniaturized integrated design, downhole environmental reliability protection, and low‑noise high‑stability output. It satisfies high‑voltage power demands for logging tools in conventional, deep, ultra‑deep and geothermal wells, providing standardized design guidelines for localization and performance improvement of core components in domestic oil and gas logging equipment. Addressing extreme high temperatures, confined spaces, severe vibration and low electromagnetic interference in downhole logging applications, the methodology adopts a universal framework of "high‑frequency isolated flyback topology + high‑temperature optimized linear regulator + fully digital high‑temperature adaptive control", combined with compact cylindrical integration and comprehensive high‑temperature reliability enhancement. It overcomes critical limitations of conventional high‑voltage power supplies regarding long‑term stability at 175℃~225℃, large size, poor vibration resistance and excessive EMI. The flyback topology is selected for its simplicity, low component count, compact structure, high step‑up ratio and galvanic isolation, ideal for narrow cylindrical downhole layouts. Optimized for wide input voltage tolerance and high‑temperature stability, it is followed by a linear regulator to eliminate switching ripple, achieve ultra‑low output noise and support high‑precision weak signal acquisition. Eight core design principles are specified: 1. Ultra‑high‑temperature optimized flyback topology and transformer design. Magnetic cores adopt high‑temperature low‑loss Mn‑Zn ferrite or nanocrystalline alloy with Curie temperature ≥300℃ to avoid sharp permeability drop, saturation or excessive loss at 225℃. Operating flux density is derated sufficiently to prevent saturation at high temperatures. Windings use polyimide insulated high‑temperature wires ≥250℃ with interleaved layered winding to reduce leakage inductance, high‑frequency AC loss and parasitic capacitance, minimizing voltage spikes, switching loss and EMI. Insulation uses composite polyimide film and ceramic materials ≥250℃. Transformers are vacuum encapsulated with high‑temperature high‑thermal‑conductivity epoxy with glass transition temperature ≥250℃ to enhance insulation, heat conduction and mechanical shock resistance. 2. Wide input voltage adaptation. Peak current mode control combined with mixed PWM/PFM modulation maintains stable output and high efficiency under large input fluctuations and wide load variations. The input range covers 50%~150% nominal voltage with reliable startup and full power at the lowest input. Input under‑voltage lockout, over‑voltage protection and surge suppression prevent damage from cable voltage spikes. 3. High‑temperature component selection and consistency optimization. All components are high‑temperature grade, military grade or dedicated for oilfield logging with operating ranges of −55℃~+225℃. Semiconductors prefer SiC MOSFETs, JFETs or high‑temperature silicon MOSFETs for low leakage, low switching loss and thermal stability above 200℃. Rectifiers use SiC Schottky diodes to eliminate reverse recovery loss. Capacitors employ high‑temperature ceramic, PPS film or mica types, excluding electrolytic capacitors prone to severe aging. Resistors use high‑stability metal film, metal foil or wirewound types with low temperature coefficient. Control ICs, MCUs and references are logging‑specific high‑temperature components. All devices undergo high‑temperature burn‑in and temperature cycling screening to ensure consistency and long‑term reliability. 4. Fully digital high‑temperature adaptive control. A dedicated high‑temperature logging MCU implements full digital control with thermal compensation, multi‑mode operation, protection and communication. Full‑temperature adaptive algorithms monitor ambient temperature, junction temperature and transformer temperature, dynamically adjusting switching frequency, peak current limits, loop compensation and dead time to counteract parameter drift across −40℃~+225℃, maintaining loop stability and output accuracy better than ±0.5% while retaining soft switching. Mixed PWM/PFM optimizes efficiency across light and heavy loads. Full‑range temperature calibration is stored in non‑volatile memory to suppress temperature drift below ±1%. Integrated CAN and RS485 interfaces support remote configuration, telemetry and fault reporting for intelligent logging systems. 5. Miniaturized cylindrical integration. Flexible or circular rigid PCBs adopt axial layered stacking to arrange power conversion, transformer, rectification-filtering, control and protection units along the tool axis, maximizing space utilization. Surface‑mount micro high‑temperature components reduce size and parasitic effects. The entire power supply is fully encapsulated in high‑thermal‑conductivity epoxy closely bonded to the tool housing for enhanced insulation, efficient heat conduction to drilling fluid and superior shock resistance, achieving outer diameter ≤50 mm, length ≤300 mm and power density ≥100 W/in³. 6. Low‑noise and electromagnetic compatibility design. Full‑range EMI suppression is implemented through topology optimization, shielding, filtering and grounding. Soft switching reduces dv/dt and di/dt at the source; post linear regulation eliminates switching ripple below 0.1% peak‑to‑peak. Double shielding adopts inner permalloy magnetic shielding and outer stainless steel/titanium electric shielding with shielding effectiveness ≥60 dB. Independent shielded cavities isolate power and control circuits. Multi‑stage EMI filtering suppresses conducted interference on input and output, with π‑type filtering at high‑voltage outputs. Strict single‑point grounding separates power, analog, digital and shield grounds to eliminate ground loop noise. 7. Vibration shock resistance and downhole environmental protection. Integrated cylindrical metal housing improves structural rigidity. All components are surface‑mounted and reinforced; heavy devices such as transformers are fully encapsulated against vibration‑induced fracture. PCBs are mechanically fixed with metal supports. Aviation‑grade anti‑loose connectors enhance reliability under hundreds of g shock. Full encapsulation provides high pressure resistance above 100 MPa and immunity to hydrogen sulfide and drilling fluid corrosion. Creepage distance enhancement prevents surface discharge under high humidity and corrosive conditions. 8. Fast dynamic response and wide load adaptation. Dual current‑voltage closed‑loop control with load feedforward enhances bandwidth and transient performance. Output deviation remains below ±2% with settling time <100 μs during step load changes from 10% to 100%, ensuring stability across no‑load to full‑load operation for diverse logging modes. Thermal design and reliability optimization under extreme high temperatures run throughout the methodology. Thermal management relies on full encapsulation conductive heat transfer combined with housing convection to drilling fluid. Power components are tightly coupled to thermally conductive substrates and the tool housing to eliminate local hotspots, keeping junction temperatures below 70% of ratings. Aggressive derating reduces electrical, thermal and magnetic stress to extend service life. Component‑level and circuit‑level redundancy ensures seamless switchover upon single‑point failures. Comprehensive hardware‑software dual protection includes under/over‑voltage, over‑current, short‑circuit, over‑temperature and arc protection with fast response <1 μs and auto recovery for transient faults, together with watchdog reset to guarantee continuous logging operations. This methodology delivers a complete technical solution covering high‑temperature topology adaptation, full‑range temperature optimization, miniaturization, environmental protection and low‑noise stable output, fundamentally resolving traditional drawbacks including limited high‑temperature endurance, bulky size, poor vibration resistance and high EMI. It enables continuous stable operation up to 225℃, achieves compact cylindrical integration with power density exceeding 100 W/in³, ensures robustness against severe vibration and high pressure, and provides ultra‑low ripple and EMI compatible with high‑precision logging measurements. Widely applicable to conventional, deep, ultra‑deep and geothermal wells for logging tools, while drilling systems and formation testers, it provides critical technical support for domestic substitution and performance breakthroughs in China’s oil and gas logging equipment.