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Power supply guide

Guide for Classification of Power Supply Types

This document clearly and standard-neutrally defines when an electrical product is considered:

  • battery powered
  • DC powered
  • AC powered (single- and multi-phase)

The definitions apply from the perspective of electromagnetic compatibility (EMC), radio assessment, and electrical safety. The decisive factor is always the intended operating condition of the product.

1. Basic Principles of Classification

The classification of a product based on its power supply is determined exclusively by the type of energy input during intended operation. Neither industry of use nor marketing terminology is relevant for regulatory assessment.

Key rules:

  • Intended use and operating condition are decisive, not the place of use.
  • Each intended operating mode must be considered separately.
  • Internal voltage conversions do not change the category.

2. Battery Powered

Definition:

A product is considered battery powered if it is operated exclusively from an internal battery or rechargeable battery and has no wired external energy input.

The battery may be primary (non-rechargeable) or secondary (rechargeable). Rechargeability is irrelevant for classification.

EMC perspective:

  • No conducted emission or immunity tests.
  • Radiated emissions are always required.
  • ESD tests are always relevant.

Radio perspective:

  • Radio assessment is independent of the power supply.

Electrical safety:

  • Typically SELV / ES1.
  • No mains voltage risks.

Examples:

  • Remote control
  • Mobile sensor with internal battery
  • Handheld device in battery operation

3. DC Powered

Definition:

A product is considered DC powered if it is supplied via an external DC connection and has no direct connection to the public AC mains.

Typical DC sources:

  • USB, USB-C, Power over Ethernet (PoE)
  • Industrial 24 V DC supply
  • Vehicle electrical system (12 V / 24 V DC)

EMC perspective:

  • Conducted emissions on DC ports.
  • Immunity tests on DC lines.
  • No testing on AC mains.

Radio perspective:

  • External supply lines may act as antennas.

Electrical safety:

  • SELV / ES1 or ES2 depending on DC voltage.
  • No direct mains voltage hazard inside the device.

Examples:

  • Sensor with 24 V DC supply
  • IT device with external power supply
  • Battery device during charging

4. AC Powered (mains supplied, single- and multi-phase)

Definition:

A product is considered AC powered as soon as it is directly or functionally connected to the public AC mains. This applies to both single-phase and multi-phase systems.

AC supply types:

  • Single-phase: L / N / PE
  • Two- or three-phase: L1 / L2 / L3 / N / PE

EMC perspective:

  • Conducted emissions at the mains connection.
  • Surge, burst, and conducted RF tests.
  • Voltage dips and interruptions.

Radio perspective:

  • Mains lines can act as interference paths.

Electrical safety:

  • Increased requirements due to mains voltage.
  • Protection class I, II, or III.
  • Special requirements for multi-phase systems.

Examples:

  • Industrial equipment with 400 V three-phase connection
  • Household appliance with mains plug
  • Docking station with mains connection

5. Summary Key Points

  • Not the battery type, but the connection determines classification.
  • Every intended operating condition must be evaluated.
  • As soon as a device is connected to the public mains, it is AC powered.
  • Technical characteristics determine the category, not the industry.

6. Special Cases and Gray Areas of Power Supply

6.1 Battery + Charging Port

Devices with an internal battery and charging port must be classified depending on the operating condition.

  1. Battery present, charging port not connected → Battery Powered
  2. Battery present, charging port connected (charging or mains operation) → DC Powered or most likely AC Powered (depending on the connected supply)
  3. All intended operating modes must be evaluated from EMC, radio, and safety perspectives.

Note:

Charging operation is often a technically critical condition (worst case), as charging circuits, DC/DC converters, and radio modules may be active simultaneously.

6.2 Battery + USB Data Port

Devices with a battery and an additional USB port must be evaluated based on the actual

electrical function of the USB port.

  1. USB port used for data only → Battery Powered
  2. USB port supplies power fully or partially → DC Powered

Important:

It is not the connector type but the electrical function of the port that matters.

6.3 Hybrid Devices with Automatic Switching

Hybrid devices can draw power from multiple sources simultaneously or alternatively (e.g. battery + external DC supply).

  1. The classification depends on the currently active energy source.
  2. For EMC and radio testing, the most critical operating condition is decisive.
  3. In practice, this is often operation with external supply, as cables create additional coupling paths.