Glossary

Circuit technique in forward converters where the transformer core is actively rather than passively demagnetized after each switching cycle. This reduces losses and component stress and enables the smallest form factors with maximum efficiency – used in the Demke 400 series.

Autonomously navigating vehicles in intralogistics and production (German: FTS – fahrerlose Transportsysteme). Their controllers, sensors and communication are typically powered from the traction battery via compact buck-boost converters, keeping the on-board network stable even with fluctuating battery voltage.

A boost converter converts the input voltage Vin into a higher output voltage Vout, e.g. 12 V to 24 V. It is used when the source supplies a lower voltage than the load requires.

Production designation: the device is fully developed and manufactured upon order. Initial manufacturing costs may apply; from a minimum order quantity of 25 pieces they are reduced to a minimum.

A buck converter converts the input voltage Vin into a lower output voltage Vout. Typical application: powering controllers, sensors and communication modules from higher battery or vehicle networks, e.g. 80 V down to 24 V.

These converters can convert an input voltage Vin into a higher or lower output voltage Vout. They deliver a stable output voltage even when the input fluctuates around the output level – indispensable in battery-powered systems with widely varying storage voltage.

A load with a high capacitive component, e.g. buffer capacitors or supercaps at the converter output. High capacitances cause large charging currents at switch-on. Thanks to CC/CV control and soft start, many Demke converters drive practically unlimited ("infinite") capacitive loads.

Specifies the constant-current/constant-voltage characteristic of a converter. In the normal load range the voltage is regulated; in the overload range the current is regulated instead. This behavior is used in battery charging applications: the battery is charged with constant current until the end-of-charge voltage is reached.

Ratio of output power to input power at the nominal output current.

Ratio of output power to input power at 10% of the nominal output current.

Ratio of output power to input power at 50% of the nominal output current.

The parasitic capacitance between input and output circuit across the isolation barrier, specified in nanofarads. In Demke converters it consists of the transformer winding only. A small coupling capacitance reduces leakage currents and the transfer of fast interference pulses across the isolation.

Product designation of Demke DC/DC converters; the old name "DC-Transformer" was renamed to "DC-Converter". A DC-Converter converts one DC voltage into another and provides the variable current needed to transfer power. It contains all relevant subassemblies such as control loop, power switches and EMI filters to transfer power with maximum quality.

Products with the suffix “E” are equipped with an internal decoupling diode. It prevents a battery or another voltage source connected to the output from feeding current back through the DC/DC converter towards the input side.

The decoupling diode is particularly useful in parallel and redundant configurations to prevent unwanted reverse currents between voltage sources or converters.

In galvanically isolated DC/DC converters, such as the Demke 3xx and 7xx series, reverse current is inherently blocked by the converter topology. An additional decoupling diode is therefore generally not required.

The reduction of a converter's available output power as ambient temperature rises. Many standard converters must be throttled or oversized above roughly 50–60 °C. Demke DC/DC converters operate without derating: full rated power from −40 °C to +85 °C.

Road approval for vehicle components according to UNECE Regulation No. 10 (EMC of automotive electronics). The E-mark with country code confirms type approval, e.g. E13-10R-05 for the DC-Converter 729-57-ON, permitting use in road-approved vehicles.

Efficiency describes the ratio of output power to input power. For physical reasons this value is always below 1. An efficiency specified by Demke Electronic is measured at the converter terminals. Datasheets state it at three operating points: light load (10% of nominal output current), partial load (50%) and full load (100%).

EMC (electromagnetic compatibility) describes a device's ability to neither be disturbed by electromagnetic interference nor disturb other equipment. Integrated EMI input and output filters ensure that Demke converters meet the immunity and emission standards of the EN 61000 series – without external filter circuitry.

European family of standards for electromagnetic compatibility. Relevant for Demke converters: EN 61000-6-2 (industrial immunity), EN 61000-4-2 (ESD), 4-3 (RF fields), 4-4 (burst), 4-5 (surge), 4-6 (conducted disturbances) as well as EN 61000-6-3/6-4 (emission for residential and industrial environments).

Control input for externally switching on a DC/DC converter.

The DC/DC converter is switched on by connecting the ON pin to the positive input potential or pulling it High. When the ON pin is open or Low, the converter remains switched off.

The ON logic therefore operates in the opposite way to the Shutdown (SD) logic: with the SD pin, an open input means normal operation, whereas the ON pin requires a High signal to enable the converter.

Product status: the device is no longer manufactured or no longer recommended for new projects. For many EOL devices, improved successor products are already available.

Isolation between input and output designed for functional purposes (potential separation) but not certified as a safety barrier against electric shock. Demke's isolated DC/DC converters (THT) are function-isolated converters for PCB mounting.

Electrical separation of input and output circuits; energy is transferred via a transformer. Galvanic isolation protects against ground loops and interference and is a prerequisite for many safety- and standards-relevant applications. Insulation strength is specified in VDC, e.g. 2100 VDC primary to secondary.

AC component at switching frequency superimposed on the input voltage. Measured in millivolts peak-to-peak with a bandwidth limit of 20 MHz.

While the DC/DC converter operates, waste heat is generated and dissipated directly to the environment through the metal housing. The aluminum case thus doubles as a heat sink – no external fan is required.

The time from applying the input voltage until the output voltage is available, including internal initialization (e.g. 300 ms). Not to be confused with the soft-start ramp (e.g. 30 ms), which describes only the controlled ramp-up of the output voltage at the end of the switch-on time.

The typical input current of the converter without a connected load, measured at nominal input voltage (e.g. 50 mA). A measure of the device's own consumption at idle.

The maximum voltage permitted at the input for short durations (e.g. 125 VDC), such as during transients in the vehicle network. It must not be applied permanently – continuous operation is only permissible within the specified input voltage range.

The input voltage at which the converter starts operating (e.g. 18.0 VDC). It is deliberately set above the undervoltage lockout threshold (e.g. 16.5 VDC) – this hysteresis prevents the converter from constantly switching on and off with a soft, sagging source.

The voltage range at the input within which the converter meets its full specification, stated from minimum to maximum DC voltage. Example: 18 to 110 VDC for the DC-Converter 755-24-SD.

The test voltage that the galvanic isolation withstands between primary side, secondary side and case, specified in VDC or VAC. Example: 2100 VDC primary to secondary and primary to case for the DC-Converter 755-24-SD.

The IP rating classifies an enclosure's protection against solid objects and water. IP69K is the highest level (ISO 20653): dust-tight and resistant to high-pressure and steam-jet cleaning. Demke converters achieve IP69K through aluminum housings, full PU potting and sealed cable entries.

International standard for quality management systems. Demke DC/DC converters are manufactured to ISO 9001:2015 – by the long-standing production partner Elotec Fischer GmbH in Germany; every device is 100% tested before delivery.

The product suffixes “L” and “LEX” identify variants with a particularly low minimum input voltage.

An L variant can operate at a lower input voltage than the corresponding standard version. LEX extends the usable input voltage range even further towards lower voltages.

Example: 257E-24-SD, 257LE-24-SD and 257LEX-24-SD differ, among other characteristics, in their minimum input voltage.

The exact voltage limits are product-specific and are specified in the respective datasheet.

The highest current the converter draws at the input under full load (e.g. 27 A). The basis for dimensioning cable cross-sections, connectors and upstream fuses.

The minimum load required for the converter to maintain the specified output voltage at full accuracy, stated as a percentage of nominal current (e.g. 5%). Below the minimum load the converter remains safe to operate, but the output voltage may rise slightly (see No-Load Output Voltage Increase).

Minimum order quantity for project-specific, custom DC/DC converters. Since custom devices are manufactured on a project basis only, they carry a minimum order quantity due to the increased production costs of small batches; one-time costs may apply.

Statistical average operating time between two failures of a repairable system, a key reliability figure. Thanks to a high-quality bill of materials, Demke DC/DC converters achieve MTBF values of up to 1.5 million hours.

Production designation: the device is series-produced and available from stock, at short notice or usually within 6 weeks.

Statistical mean time until a device fails. The failure probability is calculated as Px(t) = 1 − e^(−t/MTTF).

The rise of the output voltage in the unloaded state compared to the nominal value under load, stated in percent (e.g. 4%). Sensitive loads should be rated for this slightly elevated no-load voltage, or a minimum load should be provided.

The converter can be operated permanently without a connected load without being damaged. Note the specified no-load output voltage increase and, where applicable, the minimum load required to maintain full voltage accuracy.

The input circuit and the output circuit are electrically connected. The positive input and output voltages reference the same potential. Non-isolated converters are more compact and efficient but require a common ground concept.

Typical maximum current at the output of the DC/DC converter under normal operating conditions, specified in amperes DC. Example: the DC-Converter 755-24-SD delivers up to 19 A at 24 V output (450 W).

Protective function that safeguards converter and load against impermissibly high voltage at the output – both against internally caused overvoltage (e.g. 40 VDC threshold) and against voltage fed back from outside, such as from a connected battery (feedback protection, e.g. up to 35 VDC on the 755-24-SD).

The maximum continuous power the converter can deliver at its output, specified in watts. Demke DC/DC converters cover the range from 1 W to 1200 W – without power derating across the entire temperature range from −40 °C to +85 °C.

The permissible deviation of the output voltage from the nominal value under rated conditions, stated in percent (e.g. ±2%). It covers the tolerances of control loop and reference within the specification and indicates how precisely the converter holds its setpoint.

Brief exceeding of the target output voltage at switch-on. Demke converters settle overdamped, i.e. without overshoot – sensitive loads are never exposed to an excessive voltage.

Purely resistive (ohmic) load without capacitive, inductive or active components – the simplest load case for a converter.

A Demke Electronic service: the systematic analysis of failures, weaknesses and design flaws in existing power electronics – from field troubleshooting to root-cause analysis at circuit level, including recommendations for remedy.

Complete filling of the housing with polyurethane potting compound. The potting protects the electronics against moisture, dust, vibration and mechanical shock, improves heat dissipation and is the basis for protection classes up to IP69K and climate-proof operation from −40 °C to +85 °C.

The converter's current consumption in the switched-off state (shutdown mode), specified in milliamperes (e.g. 2.5 mA). Relevant for battery-powered systems in which the converter is disabled via the SD pin but remains connected.

Package of standards for electronics on rail vehicles: EN 50155 defines requirements for electronic equipment (temperature, voltage fluctuations, interruptions), EN 45545 fire protection, EN 61373 shock and vibration resistance, and EN 50121-3-2 EMC. Demke converters are certified to these standards on customer request.

Two EU regulatory frameworks for material compliance: REACH governs the registration and restriction of chemical substances, RoHS restricts hazardous substances (e.g. lead, cadmium) in electronics. Demke DC/DC converters are REACH and RoHS compliant; the declarations are available for download.

Return authorization for shipments back to the manufacturer. Before any return shipment, an RMA number must be requested in writing and a precise fault description enclosed – this ensures fast and smooth processing.

Short-circuit-proof converters limit the output current to a safe value under overload or short circuit. Demke converters are permanently no-load and short-circuit proof and are not damaged even by a sustained short circuit.

Control input for externally switching off a DC/DC converter without disconnecting the input voltage from the device.

For normal operation, the SD pin remains open. Connecting the SD pin to the negative input potential or pulling it Low switches the DC/DC converter off.

For cabled devices, an unused SD wire should not be left exposed. It should be properly insulated or otherwise protected against unintended contact.

Converter topology in which energy is transferred through the transformer during the switch's conduction phase. All DC/DC converters of the Demke 400 series operate on the single-phase forward converter principle with active demagnetization, enabling the smallest form factors with maximum efficiency.

The output voltage is ramped up slowly and in a controlled manner at switch-on. This reduces inrush current peaks and prevents upstream fuses from tripping. Example: 30 ms soft-start ramp on the DC-Converter 755-24-SD.

The permissible ambient conditions for the device when not in operation: storage temperature range (e.g. −10 °C to +65 °C), maximum relative humidity (e.g. 75% RH) and maximum storage duration under worst-case conditions. The storage temperature range may differ from the operating range – both are stated in the datasheet.

Electrochemical double-layer capacitor with very high capacitance, used as short-term energy storage or to bridge voltage dips. Demke buck-boost converters charge supercaps via the CC/CV characteristic and make optimal use of their energy even as the storage voltage drops significantly.

Control input used to switch between product-specific output voltage settings.

Depending on the DC/DC converter, the SH pin can be used to select between different output voltage setpoints. The exact switching logic and corresponding voltage values are product-specific and are specified in the respective datasheet.

Example: On the 757-27-SDB4 DC/DC converter, the output voltage is 29 V when the SH pin is Low. When the SH pin is open or High, the output voltage is 27 V.

The operating frequency of the power supply: at this switching frequency an AC voltage is generated across the internal inductors, which is then rectified and smoothed. Typical value: 125 kHz for the DC-Converter 755-24-SD.

If the temperature inside the DC/DC converter exceeds the thermal shutdown threshold (e.g. +90 °C case temperature), the converter is deactivated. Restart occurs automatically as soon as the temperature falls below the hysteresis-based threshold.

Through-hole mounting: a form factor in which the converter is soldered directly onto the PCB via connection pins. Demke's isolated DC/DC converters (THT) are function-isolated converters for PCB mounting.

Datasheet abbreviations: UiNom is the nominal input voltage, IoNom the nominal output current. Many datasheet values apply under defined test conditions, e.g. "all parameters defined at Ta = 25 °C, IoNom = 19.0 ADC and UiNom = 80 VDC" – notations like "0.5IoNom" mean half the nominal current (partial load).

Input voltage range with a ratio of up to 1:10 between minimum and maximum voltage, e.g. 12 V to 120 V. A single converter thus covers multiple battery platforms (24 V, 48 V, 80 V) and tolerates static deviations of ±30% and more.

Undervoltage protection: if the input voltage falls below a defined threshold (e.g. 16.5 VDC), the converter switches off. This protects the supplying battery from deep discharge and prevents undefined operating states. Above the start-up voltage, the converter restarts automatically.

Unit notation in datasheets: VDC stands for volts direct current, ADC for amperes direct current. They make clear that the value refers to DC quantities – as opposed to VAC/AAC for AC quantities.

The DC network of a vehicle or mobile machine from which all electrical loads are supplied – common systems are 12 V, 24 V, 48 V or 80 V. DC/DC converters stabilize the on-board network and derive the voltages for controllers, terminals and sensors from it.

Development and manufacturing of power electronics without Demke branding: the finished product carries the customer's brand and integrates seamlessly into their portfolio. Demke handles circuit design, prototyping and series production in the background.