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Yes—a digital boost-PFC controller can estimate AC input power without a separate input-voltage and input-current metering pair, but it still relies on existing measurements and a converter model. In a 400 W prototype, Monolithic Power Systems (MPS) reported less than 3% estimation error from 10% to 100% load against a Yokogawa WT310E power meter. That is evidence of feasibility for that hardware and test range, not a universal accuracy guarantee. The original EE Times title, “with Additional Sensors,” is potentially misleading: the proposal is to estimate power without adding dedicated sensors.
What the estimator does—and does not remove
A power-factor-correction (PFC) front end shapes its input current to follow the AC voltage waveform. A digitally controlled PFC stage already observes or derives signals needed to regulate that current and maintain its DC output. The proposed approach reuses that information to reconstruct input current and calculate power, rather than adding a dedicated sensor pair at the AC input.
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That is not the same as operating with no sensing. The controller still needs relevant voltage and control-state information, and the estimate depends on timing, operating-mode behavior and component parameters. The distinction is between using existing control signals and adding an independent metering path.
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Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →Clear out junk files and repair common Windows errorsFree Scan →Conventional metering may use a shunt and amplifier or a Hall-effect current sensor, plus voltage sensing such as a divider or isolated circuit. It provides an independent measurement path, but adds components, board area, power use, calibration work and potentially isolation and safety-design complexity. An estimator may avoid some of that hardware; whether it reduces total product cost depends on the firmware, calibration and validation effort.
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Why a product might need real-time input power
Input-power information can support system energy reporting, efficiency trending, power-budget allocation, thermal or fan control, and supervisory decisions in multi-output equipment. MPS identifies telecom, server, workstation, adapter, battery-charger and plug-in EV systems as possible contexts for real-time power information. For those uses, an estimate may be valuable even when it is not a certified measurement.
The target is active input power: the average of the instantaneous product of line voltage and line current over time. It is not simply output voltage multiplied by output current, the apparent power calculated from RMS voltage and current, or a control-loop command that is merely proportional to expected load. Converter losses separate input power from output power, while distorted waveforms make a simple RMS product an insufficient definition of real power.
How the model-based estimate works
Conceptually, the controller reconstructs the rectified line-voltage waveform from its voltage information and line-peak estimate, then uses its control command and switching behavior to infer the inductor-current trajectory. It adjusts that reconstruction for switching timing and for the converter’s operating mode, accounts for relevant losses, and averages the resulting input power over the line cycle.
- Reconstruct the input waveform. Use available rectified input-voltage samples or a reconstructed waveform informed by the estimated line peak.
- Recover the control intent. Read the relevant control state, such as the compensation-loop signal, along with output voltage and timing or frequency information.
- Infer current behavior. Calculate the expected inductor or line-current trajectory from the converter model; direct inductor-current data can help where the controller provides it.
- Correct switching and mode behavior. Account for turn-on and turn-off delays, and use suitable relationships for continuous conduction mode (CCM), discontinuous conduction mode (DCM), and their transition region.
- Include real losses and average power. Incorporate material bridge and input-filter losses, then compute the line-cycle average of voltage multiplied by reconstructed current.
In MPS’s HR1211GY prototype, controller states including vCOMP, VIN_PK and VO were available through the controller’s UART interface. These are example signals from that implementation, not a promise that every PFC controller exposes equivalent data. A design needs enough observability, appropriate firmware access and a model matched to its topology.
Why the ideal boost equation is not enough
An ideal calculation assumes the input voltage is exact, commanded current appears without delay, components have no loss or parasitic behavior, and the converter follows a simple mode-specific waveform. Those assumptions can be adequate for control intuition but miss energy that matters when the goal is estimating actual AC input power.
CCM, DCM and the boundary between them
In CCM, inductor current does not fall to zero during a switching cycle. In DCM, it reaches zero and remains there for part of the cycle. Near the boundary, a converter may alternate between behavior represented by the two modes. A CCM-only calculation can therefore misstate current at light load or in mixed operation. In the MPS test cases, the prototype was fully CCM at 110 V RMS and 400 W, mixed CCM/DCM at 230 V RMS and 400 W, and fully DCM at 110 V RMS and 100 W. At light load, switching frequency decreased as load decreased.
Switching delays change transferred energy
The effective on- and off-times differ from ideal commanded instants because of propagation and switching delays. The paper includes those effects; its prototype used nominal turn-on and turn-off delays of 300 ns and 150 ns, respectively. Those values are parameters of the demonstrated hardware, not defaults to apply to another controller.
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DCM can include a resonant interval
After inductor current reaches zero, parasitic inductances and capacitances can produce an oscillatory interval. It changes the relationship between the intended switching waveform and the actual average current. MPS models this DCM behavior in the time domain and includes its contribution rather than treating the zero-current point as the end of all relevant activity.
Bridge and filter losses matter
Bridge-diode forward voltage and resistance in the input-filter inductors consume real power before energy reaches the boost stage. The paper accounts for these losses when relating boost-stage behavior to power drawn at the AC input. Input-filter capacitors primarily carry reactive current in the stated model, but leakage and other nonidealities can matter in a different implementation.
Other likely error contributors include component tolerances and temperature dependence, parasitic capacitance, gate-driver and sampling delays, ADC resolution, inaccurate mode detection, filter behavior, and unusual line waveforms. A line-cycle estimate may also respond poorly during startup, brownout, abrupt load steps, line dropout or burst operation unless those conditions are explicitly handled.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What MPS tested
The result comes from a specific 400 W boost-PFC prototype using the HR1211GY digital PFC/LLC combo controller. MPS reports a 90–265 V RMS input range, a 400 V output and 50 Hz line frequency. Other reported parameters were a 190 µH PFC inductor, 100 mΩ total input-filter inductance resistance, a 0.75 V bridge-diode forward-voltage parameter, a 100 kHz maximum switching frequency, and the 300 ns/150 ns nominal turn-on/turn-off delays.
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| Test detail | Reported setup or result |
|---|---|
| Prototype rating | 400 W |
| Controller | MPS HR1211GY |
| Input and output | 90–265 V RMS input; 400 V output |
| Line frequency | 50 Hz |
| Reference instrument | Yokogawa WT310E power meter |
| Load sweep and reported error | 10–100% load; error below 3% for the tested conditions |
The comparison with the WT310E is a prototype validation against a reference instrument. It does not by itself establish traceability, a metrology accuracy class or performance across production units. The article’s underlying MPS technical document is marked July 7, 2022; EE Times listed its coverage on August 21, 2024.
Read the MPS article and its technical PDF for the source’s implementation details and test material. The article’s reported sub-3% result should be read as “below 3% on this prototype over the tested load range and conditions,” not as an accuracy specification for arbitrary boost-PFC hardware.
How to decide whether to use an estimate
| Application | Practical fit |
|---|---|
| Firmware telemetry or digital power display | Often a reasonable candidate after validation against an analyzer. |
| Power budgeting or efficiency trends | Can be useful when error bounds are known and the system has suitable margin. |
| Fan or thermal-management decisions | May be suitable if the control decision tolerates estimation error and transient lag. |
| Revenue-grade or regulatory energy measurement | Do not assume suitability; the cited result is not a metrology certification. |
| Safety-critical current or overload protection | Do not rely on a model-based power estimate as the sole independent protection. |
| Different topology, controller or abnormal operating states | Derive and validate a suitable model; the published result does not transfer automatically. |
Validation checklist for a real design
- Confirm that the controller exposes or permits reconstruction of the required voltage, control, timing and mode information.
- Compare the estimate with a calibrated power analyzer at low, nominal and high line.
- Sweep from light load to full load and exercise CCM, DCM and the transition region.
- Test both 50 Hz and 60 Hz if both are in the product’s intended input range.
- Repeat at cold, room and hot temperatures, and account for component tolerance corners.
- Test startup, brownout, line dropout, load steps and any burst or other special operating mode separately from steady state.
- Report steady-state power error, transient response and accumulated-energy error separately; an estimator can perform differently on each.
- Decide whether per-unit or design-revision calibration is necessary for the application’s error target.
Dedicated sensing remains preferable when an independent measurement is required, accuracy must hold across broad production variation or aging, the input waveform is outside the modeled assumptions, or protection must remain dependable during abnormal switching and faults. The sensorless approach is most compelling when an existing digital controller provides useful state information and the product needs validated telemetry or supervisory control rather than certified metering.
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