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1Clear out junk files and repair common Windows errors2Scan for outdated or missing drivers - takes under a minute3Repair Windows errors before they cause bigger problemsTo diagnose excessive standby power, first measure the supply in a clearly defined no-load or standby state at specified input voltage and frequency. Then investigate, in order, losses from the startup circuit, light-load switching behavior, feedback and bias circuits, and the switch clamp or snubber. There is no single standby-power limit for every flyback: judge results against the product specification and the requirement for the relevant market and test state.
Establish a comparable standby measurement
Before changing components, define what “standby” means for the unit. An unloaded output is not necessarily the same as the product’s standby mode: internal circuitry may still draw power, and output terminals may still carry a load. Record the operating state, output voltage, AC input voltage and frequency, and real input power. Where practical, measure at relevant low- and high-line conditions; line voltage can materially affect the result. Do not estimate real power from RMS current alone.
For example, Texas Instruments’ 2026 TIDA-01417 report gives standby measurements for its 24 V flyback output condition of 36 mW at 90 VAC, 38 mW at 120 VAC, 38 mW at 150 VAC, 40 mW at 180 VAC, 40 mW at 230 VAC, and 50 mW at 265 VAC. These are design-specific readings, not acceptance limits for another supply. Read the TIDA-01417 report.
The available design examples do not establish one safe instrument arrangement or live-mains procedure for an arbitrary converter. Use appropriately rated, isolated instrumentation and established lab practice; do not treat a reference-design setup as a universal bench procedure.
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Trace the main loss paths
Startup network drawing from the high-voltage input
Check whether startup resistors or other startup circuitry remain connected to the rectified input during normal operation. A continuously connected resistor network draws power even when the output is unloaded, and that loss can become especially significant at high line. Compare the measured line dependence with the circuit schematic before concluding that the startup network is responsible.
For a redesign, an integrated high-voltage startup function or a controller with sufficiently low startup current may allow lower startup losses. That is a design option, not a reason to replace parts without confirming the circuit’s requirements.
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Switching activity at very light load
Find out how the controller behaves when the output load falls: does it keep switching at a fixed frequency, or does it reduce frequency or enter burst or valley operation? Switching events and gate-drive activity consume energy, while the switching device’s gate charge and output capacitance contribute to light-load loss. The controller’s actual operating mode matters; a controller’s advertised capability does not establish how a particular implementation behaves.
Texas Instruments reports that its UCC28730 example can operate down to a minimum switching frequency of 30 Hz, which it says facilitates less than 5 mW no-load power. This is a device and design capability statement, not a guaranteed result for every circuit using the controller. See the UCC28730 flyback controller.
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Feedback and bias consumption
Review the secondary-side feedback and bias circuitry in the defined no-load state. Their current draw still contributes to input power, and TI’s instructional example describes feedback circuitry dissipating tens of milliwatts—a meaningful share when the overall target is small. Primary-side regulation can eliminate the optocoupler and secondary feedback components in suitable designs, but it is a topology choice for a compatible design, not evidence that an existing secondary-feedback circuit is defective.
Switch and clamp or snubber losses
Consider switching-device gate charge and output capacitance, as well as energy dissipated in the clamp or snubber from transformer leakage. TI’s example reports that raising clamp voltage reduced temperature and improved efficiency, but warns that the primary FET must not be overvolted. Its material also notes that an RC clamp may cost less while being less accurate and dissipating more power at very light burst-mode loads.
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Do not make a blind clamp-component swap. Treat a clamp change as a design calculation and verify actual switching waveforms and device ratings before altering clamp voltage.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Use published figures as context, not pass/fail limits
TI’s examples show how widely no-load figures can vary across designs and test conditions. The values below are useful context only; they do not define an acceptable result for an unspecified product.
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| Example | Reported no-load or standby figure | Condition and qualification |
|---|---|---|
| TI instructional fixed-frequency flyback example | 150 mW at 80 VAC to 750 mW at 265 VAC | TI says the example was designed around a 75 mW no-load target. The video page does not state a publication year. Design-specific result. |
| TI improved UCC28730 example | Below 20 mW | Example result reported in TI instructional material; not a general guarantee. The video page does not state a publication year. |
| TI TIDA-01417 | 36 mW at 90 VAC; 38 mW at 120 VAC; 38 mW at 150 VAC; 40 mW at 180 VAC; 40 mW at 230 VAC; 50 mW at 265 VAC | 2026 report; 24 V flyback output condition. |
| TI TIDA-010058 | 31.6 mW at 115 V/50 Hz; 54.2 mW at 230 V/50 Hz | 2019 design report; specific dual-output design. |
| TI PMP31248 | Less than 6 mW at 230 VAC | Specific 12 V quasi-resonant reference design. The page’s publication year is not stated in the available material. |
| TI PMP40025 | Less than 75 mW at 230 VAC, no load | Specific 48 W reference design. The page’s publication year is not stated in the available material. |
Sources: TI instructional video; TIDA-01417 report; TIDA-010058 report; PMP31248 reference design; PMP40025 reference design.
Decide whether the measured result is actually excessive
Compare the measurement with the product’s own specification and the applicable standby requirement for its market, under the requirement’s defined test state and input conditions. A reference design’s reported result is not a universal target, and values from different line voltages, output states, or circuit designs are not directly interchangeable. Confirm current datasheets and local requirements before selecting a component or setting a compliance target.
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