K78xx-500R3 vs 1000R3 vs 2000R3: What to Check Before BOM Release

The suffixes create a shortlist, not a released BOM

A purchasing engineer can reasonably start with three published WEHO product identities. The K78xx-500R3 page, K78xx-1000R3 page and K78xx-2000R3 page each describe a non-isolated, stabilized, single-output module in SIP3 packaging. Each table lists output-voltage rows of 3.3, 5, 9, 12 and 15.

That common structure is useful for discovery. It does not establish that the three families share the same pin functions, pitch, body outline, height, electrical behavior or allowable operating current under the buyer’s conditions. A higher number in a family name also does not approve a higher-current part as a direct substitute on an existing PCB.

Use four gates before asking purchasing to release an exact part number:

1. Electrical target: exact output-voltage row and the full source-voltage envelope.
2. Load and temperature: every credible current state, duration, ambient and cooling condition.
3. Physical interface: controlled pin map, orientation, dimensions and straight- or curved-pin option.
4. Integration evidence: external components, output quality, protection, EMC and sample validation.

If the project is still deciding whether a shared input/output reference is acceptable, resolve that architecture question first. WEHO’s non-isolated power-module overview explains the category. This checklist begins after non-isolated conversion has become a legitimate candidate.

What do the current WEHO pages actually establish?

The safest comparison preserves the wording of each page rather than silently harmonizing it.

These are published-page statements, not independent measurements. Two details prevent a clean current-tier conclusion.

First, the K78xx-1000R3 feature list says “output 500mA,” while its table has one merged 1000 entry under “Output Current (mA) (Max./Min.).” The page does not explain which statement controls. The conflict may be a content error, but that is an inference—not authority to correct it in a BOM.

Second, every part number in the K78xx-2000R3 table carries an (L) suffix that is absent from the page title. The page does not define that suffix. Ask WEHO to identify the exact orderable code and the meaning of the pin option before copying a model into purchasing data.

The pages also say that straight or curved pins can be packaged, but they do not provide an ordering-code map, pin drawing or dimensions in the supplied page bodies. “SIP3” and “three pins” are package descriptions, not a mutual-compatibility certificate.

Gate 1: match the exact voltage row to the source envelope

All three tables use 24 as the standard input value. Their ranges are not identical across every family. The table bodies do not print a voltage unit beside the numeric cells, so the page notation is reproduced below without adding an unstated convention.

Select from the range belonging to the exact output row, not from the most permissive number elsewhere in the family. Record the source at normal operation, low-line operation, high-line operation, startup, shutdown and any credible disturbance that the module is expected to survive or operate through. The published ranges alone do not define transient immunity or absolute-maximum behavior.

If the source envelope crosses a published boundary, do not average it into compliance. Either resolve the source condition, obtain controlled evidence that covers it, or remove that variant from the shortlist.

Gate 2: turn the load into a reviewable current envelope

“The board uses about 400 mA” is not enough information to choose a current tier. Build the requirement from equipment states and keep each number tied to a drawing, component specification or controlled measurement.

Add a project-owned design allowance only after its purpose is documented. Do not use an arbitrary percentage to hide unknown startup current, temperature derating or a future load that has not been specified.

Then ask the supplier to map this envelope to the exact part number. The current pages do not state whether the single table value is a continuous maximum, how it changes with input voltage or temperature, or how the “Max./Min.” column label should be interpreted when only one number is shown. Until those definitions are supplied, the table value is a screening entry—not a release limit.

Gate 3: prove form and fit from an exact drawing

The compatibility wording differs between the pages: the 500R3 and 1000R3 pages refer to the K78xx series, while the 2000R3 page refers to the LM78xx series. None of the three supplied page bodies publishes the information needed to establish mutual interchangeability.

Request a controlled drawing for the exact candidate and compare:

• pin number, function, order and viewing orientation;
• pin pitch, diameter or section, and insertion requirements;
• body width, depth and height;
• straight- versus curved-pin configuration and its order code;
• keep-out area, nearby-component clearance and assembly access;
• board hole, pad, soldering and inspection requirements, where applicable.

For an existing assembly, compare the drawing with both the released PCB data and a controlled observation of the actual board revision. For a new design, put the supplier drawing revision in the component-library record. A generic three-pin symbol or an AI-generated component image must never become footprint evidence.

Gate 4: close the electrical and thermal integration gaps

Each page claims an operating-temperature range of -40 °C to +85 °C, efficiency “up to 96%,” no-load current “as low as 0.2MA,” and no need for an external heat sink. Those phrases lack the conditions needed for a design-release decision.

Do not normalize 0.2MA to 0.2 mA without confirmation. Do not interpret “no external heat sink” as full-load approval at +85 °C. Request the applicable derating information, measurement conditions and mounting assumptions for the exact variant.

The efficiency columns also require clarification. Their header says “Min./Typ.,” but every printed pair places the larger number first. The 500R3 feature list says “up to 96%,” while none of its five table pairs contains 96. Preserve the source entries; do not reverse the pairs or build a loss calculation from them until their meaning and test conditions are confirmed.

The maximum capacitive-load rows provide another reason not to treat the families as identical:

A maximum capacitive-load value does not identify a required minimum capacitor, permitted ESR, placement rule or startup behavior. Ask for the complete external-component network and its conditions. Also obtain the project’s required output tolerance, line/load regulation, ripple/noise measurement method, transient response, switching-frequency information, protection behavior and EMC evidence. None of those fields should be borrowed from another K78xx product name.

Use one BOM gate for every candidate

Keep one row per exact orderable variant. A blank or conflicting item remains open; it is not converted into an implied pass.

This gate separates product discovery from qualification. It also prevents a supplier clarification from remaining in an email while the PCB library, BOM and drawing continue to carry an older assumption.

How should each family be treated today?

K78xx-500R3 can remain a shortlist candidate when its exact voltage row covers the source and the buyer’s load may fit within the controlled current and thermal capability supplied for the precise model. Its feature text and table both show 500 mA, but that agreement does not supply derating, pinout or output-quality evidence.

K78xx-1000R3 requires a written current clarification before selection. The page identity and five model rows are usable for directing an inquiry. The conflicting 500 mA feature text and 1000 mA table entry prevent a responsible release limit from being taken from the page alone.

K78xx-2000R3 can remain a shortlist candidate only under the table’s exact (L) identity pending confirmation. Its input ranges differ from the other two families in every listed voltage row, and its 12 V maximum capacitive-load entry also differs. Confirm the suffix, pin configuration and all operating limits before treating it as the higher-current option.

None of the three should be described as a drop-in upgrade for another. That conclusion requires an exact, revision-controlled form/fit/function comparison and the relevant board-level validation.

Send an evidence-ready selection request

For a useful response, send WEHO one compact requirement pack:

1. required output voltage and tolerance at the load;
2. minimum, nominal and maximum source voltage, plus relevant startup or disturbance conditions;
3. continuous, startup and short-duration load states with duration and repetition rate;
4. ambient range, enclosure, airflow and mounting orientation;
5. PCB footprint or drawing, height limit and required pin form;
6. existing input/output capacitors and any change constraints;
7. ripple, transient, protection, EMC and compliance requirements;
8. target quantity, project timing and required document revisions.

Ask for the exact orderable part number, current datasheet, pinout and dimensional drawing, current/derating definition, external-component requirements and written resolution of any page conflict. Use the WEHO contact page for that model-level evidence request. Browse the wider WEHO product catalogue only if the K78xx shortlist cannot meet the confirmed requirement.

The requested outcome is an exact-variant evidence check, not an unsupported promise that one of the three families will fit.

Soalan Lazim

Are K78xx-500R3, K78xx-1000R3 and K78xx-2000R3 pin-compatible with one another?

The supplied page bodies do not establish that. They publish SIP3 packaging and straight/curved-pin language, but no common pin map, dimensions or cross-family compatibility statement. The 500R3/1000R3 wording refers to K78xx; the 2000R3 wording refers to LM78xx.

Does K78xx-1000R3 have a 1000 mA output rating?

Its table shows a single 1000 entry in the output-current column, while its feature text says output 500 mA. Obtain written clarification and a controlled datasheet before using either number as a design limit.

Do the three families have the same input range?

No. The 500R3 and 1000R3 pages print the same range for corresponding output rows, but the 2000R3 page prints a different range in all five rows. Match the exact output variant to the full source envelope.

Does “no need for external heat sinks” mean full output at +85 °C?

The pages do not state that condition. Confirm the exact variant’s derating, mounting and cooling requirements before setting an allowable load.

Can the maximum capacitive-load row be used as a recommended output capacitor?

No. It is a maximum entry, not a complete component recommendation. Minimum capacitance, ESR, placement and startup conditions are not supplied in these page bodies.

Decision summary

• SHORTLIST: the exact voltage row and published input range cover the requirement, but controlled model evidence is still being collected.
• HOLD: current definition, 1000R3 conflict, (L) identity, pinout, dimensions, derating or integration data remains unresolved.
• REMOVE FROM SHORTLIST: a confirmed source, load, thermal, mechanical or output-quality requirement is outside the exact model’s documented capability.
• RELEASE TO BOM: only after the exact part, revision and supporting evidence match the approved design and validation record.

Source and evidence boundaries

• WEHO K78xx-500R3 product page — used only for its published identity, feature text and five-row table.
• WEHO K78xx-1000R3 product page — used with the 500 mA/1000 mA conflict preserved.
• WEHO K78xx-2000R3 product page — used with the table’s (L) suffix and distinct input/capacitive-load entries preserved.
• What Is a Non-Isolated Power Module and Why Use It? — category context only; it is not evidence of exact K78xx model performance or suitability.