Concept image generated with AI. Its unlabeled traces are decorative and are not a WEHO measurement, product, customer test, timing value, or acceptance result.
How should multi-output rail order be verified?
Direct answer: Capture every relevant rail simultaneously at the actual load and during both power-up and power-down. Define the equipment's observation thresholds, permitted order, delay windows, monotonic behavior, residual-energy boundary, and back-power conditions before testing. Repeat the documented operating and interruption cases, preserve the raw captures, and compare only with the load manufacturer's requirements. Do not infer sequencing from nominal output labels or a single-channel trace.
Multi output power supply sequencing is a time-domain system question. A supply may present several correct steady-state outputs while the connected logic, analog, or bipolar circuitry still sees an unacceptable order during startup, shutdown, interruption, or restart. The decision must therefore bind one exact supply configuration, one exact load configuration, one event definition, and one controlled set of acceptance rules.
This article explains how to build that evidence. It does not publish timing behavior for a WEHO model, prescribe an oscilloscope setup, or define limits for a customer's equipment.
Define sequencing from the load's point of view
XP Power's guide defines sequencing as the desired order of activation of the outputs of a multiple-output power supply. The critical word is “desired”: the connected equipment, not the supply's product name, determines whether the observed order is acceptable. The definition does not establish any WEHO rail order, delay, monotonicity, turn-off behavior, or load compatibility.
Start with the load manufacturer's controlled requirements. Translate them into observable events without changing their meaning. The record should identify:
- every rail and reference point that matters to the load;
- the event that starts the timing comparison;
- the threshold or state that defines each rail as active or inactive;
- permitted order and any time relationship between rails;
- requirements for monotonic rise or fall if stated by the load owner;
- behavior required during interruption, restart, standby, and controlled shutdown;
- conditions under which one interface can back-power another; and
- the owner who decides whether the capture closes the requirement.
If the load document is silent, do not invent an acceptance window. Record the requirement as open and ask the equipment owner to define it.
Build one configuration card before connecting instruments
The configuration card ties the result to a reproducible system. Give it a unique ID and preserve every later change as a new revision. At minimum, record:
| Configuration field | What to freeze | Why it matters |
|---|---|---|
| Supply identity | exact item, model or variant evidence, revision references and relevant settings | neighboring variants may not share the same behavior |
| Load identity | board, assembly, firmware and operating mode | loads alter startup and discharge behavior |
| Rail map | supply terminal, load node, local reference and probe label for each channel | detached traces cannot be interpreted reliably |
| Source event | input source, switching point, starting state and interruption definition | different events can produce different trajectories |
| Harness and path | cables, connectors, distribution, protective devices and return topology | path impedance and stored energy belong to the observed system |
| Auxiliary connections | programmers, communications, test fixtures and external supplies | another connection may back-power a rail |
| Environment and repetition | controlled project conditions and repetition rule | evidence must state the scope it actually covers |
| Acceptance authority | source document, criterion owner and reviewer | the instrument does not decide suitability |
Do not use a product photograph as the configuration card. A photograph can support traceability, but it cannot expose internal settings, firmware, hidden auxiliary connections, or the load's acceptance rule.
Plan simultaneous measurement
Tektronix's application note explains measuring power-supply turn-on and turn-off delays when a supply is controlled through its AC mains input. This supports the general value of observing transition timing; it does not provide a WEHO setup, channel assignment, threshold, result, or pass criterion.
Use enough synchronized channels to observe every rail and control signal required for the decision in the same event. When all relevant nodes cannot be captured together, document how separate acquisitions will be correlated and what uncertainty that introduces. A collection of unrelated single-channel screenshots should not be presented as simultaneous order evidence.
For every channel, record the probe type, measurement point, local reference, range, bandwidth or filtering decision, attenuation, channel label, instrument identity, and calibration status required by the organization's procedure. The qualified test owner should assess loading, common-mode, grounding, isolation, and equipment-safety constraints before connecting any probe. This article supplies no connection instruction.
Separate six event families
Author-built conceptual workflow. It contains no waveform, voltage, timing value, probe connection, pass limit, or WEHO performance claim.
Do not compress every transition into one “startup test.” Create a matrix whose rows are the events relevant to the real equipment:
- Initial energization: the defined starting state is fully discharged or otherwise documented by the load owner.
- Warm restart: energy remains in at least part of the system and the source is reapplied under a defined condition.
- Short interruption: the input changes for a project-defined interval and returns before all rails reach their initial state.
- Controlled shutdown: the system receives its normal shutdown command or source removal sequence.
- Abrupt removal: the source is removed without the normal control path, when this case belongs to the project.
- Fault recovery: a documented safeguard or fault state clears under an authorized scenario.
These labels are organizational tools, not universal test requirements. Include only cases required by the load, system owner, risk analysis, or destination plan. For every row, state the initial condition, trigger, operating load, auxiliary connections, number of repetitions, data-retention path, and acceptance owner.
Read each capture with predeclared markers
Before opening the first waveform, define how reviewers will identify an event. A robust worksheet names the event origin and each rail's activation or deactivation marker exactly as required by the load specification. It also states how noise, ringing, plateaus, overshoot, or non-monotonic regions will be handled by the authorized analysis method. Because acceptance thresholds are application-specific, this article provides none.
For startup, review more than the first rail to move. Confirm every required order relationship, every specified delay, any monotonic behavior, control-signal alignment, and any interval during which an interface might be driven while its destination rail is not ready.
For shutdown, review the required deactivation order, discharge path, residual energy, control behavior, and any current path from an energized signal into a declining or inactive rail. The order at shutdown may not be the reverse of startup, so it needs its own criteria and evidence.
Treat back-power as a system path question
Back-power can occur when an energized rail, logic signal, communication line, programmer, or auxiliary supply feeds a node whose main rail is absent or declining. The sequence review should therefore include interfaces, not just power outputs. Map every possible cross-domain path and identify which device documents its permitted states.
Use a path table:
| Source side | Destination side | Possible path | State to review | Required evidence owner |
|---|---|---|---|---|
| active rail | inactive rail | load circuitry or shared return | startup and shutdown | load designer |
| external signal | unpowered input | interface safeguarding or internal structure | startup, shutdown and service | interface owner |
| programmer or debugger | target board | cable reference and signal pins | development and field service | test owner |
| auxiliary supply | main board | shared peripheral or communication port | interruption and restart | system architect |
This table identifies questions; it does not predict current flow. Circuit documentation and an authorized verification method must establish the actual path and acceptance boundary.
Issue a result that is narrow enough to trust
For every event row, retain the raw acquisition, exported data if used, instrument and probe record, configuration-card revision, analysis method, annotated copy, criterion source, reviewer, anomalies, and decision. Never keep only a cropped screenshot or a final delay table.
Use three decision states:
- Pass for the named configuration: every required relationship closes and the evidence package is complete.
- Hold: a configuration field, criterion, channel, capture, analysis detail, repetition, or signature is missing or conflicting.
- Investigate: a recorded observation falls outside a boundary or raises a new technical question; the original data remains intact.
The wording “for the named configuration” matters. A result for one load board, harness, source event, or supply variant should not be generalized to a neighboring configuration without a documented relevance review.
What is verified about WEHO product 779?
The sealed WEHO catalog identifies product 779 as 50W Triple output switching dc power supply 5V 12V -12V at the published WEHO product page. This article adopts only that identity and canonical URL.
Official WEHO catalog asset copied without generative alteration. It identifies the catalog record associated with product 779; visible terminals, labels, values, geometry, and construction are not adopted as specifications, rail identity, sequencing behavior, configuration, availability, certification, fit, or test evidence.
The catalog record does not establish the actual startup or shutdown order, delays, monotonicity, discharge, back-power behavior, or suitability of any variant for a particular load. Obtain current controlled documentation for the exact orderable item and verify the complete system against the load's requirements.
Use the single-output versus multi-output selection guide when the buyer task is choosing an output architecture. Use this article when the buyer task is measuring temporal order at startup and shutdown. For an item-specific documentation request, contact WEHO with the configuration card, load requirements, event matrix, and evidence request.
Часто задаваемые вопросы
Can nominal output labels prove the startup order?
No. Output labels describe identity or nominal intent, not observed temporal behavior. Startup and shutdown order require synchronized evidence from the named configuration.
Must all rails be measured in the same acquisition?
Simultaneous observation is the clearest way to establish relative order. When channel limits prevent it, the test owner must define correlation, uncertainty, and evidence sufficiency before testing.
Should shutdown be assumed to reverse startup?
No. Shutdown has its own discharge paths, residual energy, control states, and interface conditions. Measure it against separately documented load requirements.
Does the Tektronix source provide WEHO timing values?
No. It explains measuring turn-on and turn-off delays through the AC input in a general application note. It supplies no WEHO channel map, setup, threshold, result, or criterion.
What should happen if the load has no sequencing requirement?
Record the requirement as open and ask the load or system owner to define the permitted states. Do not invent a pass window from a generic article.
Is product 779 proven suitable for sensitive bipolar circuitry?
No. The sealed evidence supports only the product identity and URL. Suitability requires exact item documentation and system evidence against the load's controlled requirements.
Sources and evidence boundaries
- WEHO product 779 page — used only for the sealed catalog identity and URL; it does not establish rail order, timing behavior, configuration, availability, certification, system fit, or test results.
- Tektronix application note on power-supply sequencing (https://www.tek.com/vn/documents/application-note/verifying-power-supply-sequencing-8-channel-oscilloscope) — used only for the general context of measuring turn-on and turn-off delays; it does not provide WEHO methods or results.
- XP Power Essential Guide to Power Supplies (https://www.xppower.com/resources/guides/essential-guide-to-power-supplies) — used only for the bounded definition of sequencing; it supplies no product-specific order, delay, monotonicity, or acceptance rule.
