A quad-output switching power supply should be evaluated against the combination of rail loads that the equipment will actually use. Four correct no-load voltages and a plausible total wattage do not establish that every operating state will remain inside its permitted voltage and current limits.
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This guide helps an OEM decide whether one multi-output assembly can serve a four-rail load set. Its useful output is a simultaneous-load acceptance matrix attached to the exact supply, load configuration and document revision.
Identify the four-rail assembly
The WEHO Q-60 quad-output supply page is the specific product entry for the Q-60B specimen shown here. Freeze the full suffix and applicable rail table before comparing it with alternatives. A family wattage or a four-output description does not provide the permitted current on each rail, combined limits, minimum loads or start-up sequence.
Record the output reference pairs from the controlled terminal drawing separately. That establishes what is connected. The next task is different: demonstrate that the connected equipment’s load combinations are acceptable. Do not interpret several terminal screws as independently regulated or mutually isolated output channels.
Write a load vector for every equipment state
Name the rails and list their minimum, normal, peak and off-state demand. Keep the four currents together as a vector, for example [I1, I2, I3, I4], with the equipment state and timing attached. This preserves combinations that disappear in a single “total watts” figure.
For a calculation example unrelated to Q-60B ratings, assume rails of +5 V, +12 V, −5 V and −12 V supplying current magnitudes of 3.0 A, 1.0 A, 0.10 A and 0.20 A. Their delivered power is 5 × 3.0 + 12 × 1.0 + 5 × 0.10 + 12 × 0.20 = 29.9 W. Use voltage and load-current magnitudes for this delivered-power budget; a negative rail does not subtract its consumed power.
That result is only a total. It does not prove that a nominal 60 W supply permits the 3.0 A rail demand or that the stated load vector meets its coupled conditions. Compare every individual rail limit and every combined restriction before treating the total-power comparison as meaningful.
Select the asymmetric cases
One heavily loaded output and several lightly loaded outputs can be a more revealing condition than evenly loading all outputs. Multi-output converter designs can exhibit cross-regulation: changing the demand on one output affects voltage on another. TI’s SNVA562 application paper explains the mechanism for multi-output flyback converters. It is background for a test question, not evidence of Q-60B’s internal topology or measured regulation.
| State | Load combination to define | Observation |
|---|---|---|
| Standby | Actual low demands, including any off rails | Every receiver voltage and allowed minimum-load condition |
| One subsystem active | One rail high while the others remain light | Loaded-rail droop and other-rail rise or interaction |
| Normal simultaneous operation | Realistic concurrent currents | Per-rail limits, combined power and temperature |
| Subsystem state change | Initial/final current vectors and timing | All affected rail excursions and equipment outcome |
| Power cycle | Defined input-off/on event and connected loads | Rail timing and receiver restart requirements |
For four rails with two chosen load levels each, a complete static binary grid has 2⁴ = 16 combinations. Use engineering judgment to select permitted and relevant cases, then add real dynamic events. A convenient grid should not introduce a prohibited no-load state or replace actual equipment behavior.
Define acceptance at each receiver
Give every observed rail a voltage window, observation point and timing criterion. Measure at the receiver when the harness loss matters, while retaining source-terminal measurements where they help separate supply behavior from distribution effects. Identify bandwidth, probe reference and loading arrangement in the record.
Check the receiver’s permitted power-up and power-down relationships. Four rails starting from one assembly are not automatically simultaneous, sequenced or safe for every mixed-signal circuit. Ask for the applicable model behavior and compare it with the equipment requirement rather than assuming the enclosure supplies the required sequence.
Keep corrections inside the configuration
If a load combination fails, compare an appropriately documented multi-output candidate, a different rail allocation or separate regulated supplies. Any preload or downstream regulator changes the heat, standby demand, startup and component list. Qualify the resulting assembly; do not add a resistor by habit and reuse an earlier acceptance result.
Procurement should receive the exact full model, rail-load matrix, permitted combinations, document revision and accepted sample identity. A substitute with the same four nominal voltages must be reviewed against those records, including state changes and restart, before it enters the production BOM.
Send WEHO your four-rail load and acceptance matrix with input conditions, receiver voltage limits, timing requirements and enclosure environment. Ask for the applicable Q-60B rail specification and a candidate review against your actual simultaneous loads.
