Wide-Temperature-Range Precision Compensation for Parts-Per-Million Level Power Supplies
Achieving and maintaining parts-per-million (PPM) level stability in a high-voltage power supply is a formidable task at a constant, controlled laboratory temperature. The challenge is magnified exponentially when the supply must operate reliably across a wide temperature range, such as from -40°C to +85°C, as required in military, aerospace, or field-deployed metrology applications. Over such a span, the temperature coefficients (TC) of individual components—resistors, reference diodes, capacitors, magnetics—can combine to produce output drifts orders of magnitude larger than the PPM target. Passive component selection alone is insufficient. Active, system-wide precision temperature compensation algorithms are therefore essential, transforming the power supply into an intelligent, self-correcting instrument.
The compensation strategy is multi-layered, beginning at the component level and extending to the system control algorithm. The first line of defense is the selection of components with inherently low and predictable temperature coefficients. Bulk metal foil resistors with TCs below 1 ppm/°C, ultra-stable Zener diode references with compensated sub-circuits, and stable ceramic or film capacitors are used in critical signal paths. However, even these premium components exhibit some drift, and their TCs are not perfectly linear over the entire range. Furthermore, the cumulative effect of dozens of such components can still result in unacceptable system drift.
Thus, active compensation is implemented. This requires a detailed thermal model of the power supply. High-precision temperature sensors, such as platinum RTDs or thermistors with calibrated linearization, are strategically placed at key thermal nodes: on the voltage reference chip, on the main scaling resistor network, on the output stage transistors, and on the high-voltage transformer or multiplier. These sensors provide real-time temperature data to the digital control system.
The core of the compensation is a set of mathematical models, often derived from extensive characterization data collected during a temperature cycling test of the design. For each critical sub-circuit, a polynomial or piecewise linear function is developed that describes its output or gain as a function of its local temperature. For example, the reference voltage, Vref(T), might be modeled as Vref_25C + a*(T-25) + b*(T-25)^2. Similar models are created for the gain of the output amplifier stage and the scaling factor of the high-voltage divider.
In operation, the digital controller reads the temperatures from all sensors. It uses these models to compute the expected deviation from the ideal output voltage at the current thermal state. It then calculates a compensating adjustment to the digital setpoint sent to the control DAC. This is a predictive, feed-forward correction. For instance, if the reference temperature is measured at 45°C and the model predicts its voltage has increased by +8.2 ppm, and the scaling network at 50°C is predicted to introduce a -3.1 ppm gain error, the controller will adjust the setpoint to counteract the net +5.1 ppm error before it even appears at the output.
This process is dynamic and continuous. To be effective, the thermal sensors must have excellent long-term stability themselves and be in good thermal contact with the components they monitor. The control algorithm must also account for thermal gradients and time constants. A sudden change in load causing the output stage to heat up will not instantly affect the temperature of the reference, which may be in a separate, thermally isolated compartment. The compensation model must incorporate these thermal lags to avoid over-correcting or under-correcting during transients.
Advanced implementations may use adaptive algorithms. By periodically performing a low-intensity self-calibration routine (e.g., comparing the output to a stable internal secondary reference under different load conditions), the system can refine its compensation coefficients over time, accounting for very long-term component aging that subtly alters the original temperature models. This wide-temperature-range precision compensation elevates the power supply from a temperature-sensitive assembly to a robust measurement tool, enabling PPM-level performance in environments where conventional supplies would drift by hundreds or thousands of PPM, thereby ensuring data integrity in critical field measurements and the reliable operation of sensitive systems under extreme environmental stress.
