Common DC voltage levels

DC voltage levels:

0.7V Nominal voltage drop on normal silicon diode or similar semiconductor junction

0.8V Voltages from 0V to 0.8V are considered to be logic 0 on TTL logic IC inputs

1.25V NiCd, NiMH battery cell nominal voltage

1.5V Carbon and alkaeline battery cell nominal voltage

1.6V The voltage you normally get from a fresh alkaeline battery cell

1.8V Quite commonly used very low voltage digital circuit operating voltage (many CPU cores)

2V Lead acid battery nominal cell voltage

2V Voltages from 2V to 5V are considered to be logic 1 in TTL logic IC inputs.

3V Lithium battery nominal voltage

3.3V LVTTL logic circuits operating voltage

3.6V Typical voltage used to power cell phones (either from NiMH or Li-Ion battery pack)

4.5V operating voltage for many small electronics gargets powered from three batteries

5V TTL logic circuits operating voltage

6V operating voltage for many small electronics gargets powered from four batteries

9V Commonly used battery voltage

10V Normal control voltage limit in 0-10V and 1-10V analogue control systems (light dimming and industrial use)

12V Car battery nominal voltage

13.8V the voltage you expect to get from car 12V power when car motor is running (charging battery)

24V Truck battery.
24V Automation systems most common nominal voltage used for logic signals and and current loop powering

24V common standard input voltages in Avionics and Defense applications

28V Maximum battery charging voltage for 24V battery system (for example batteries that power automation systems).

28V common standard input voltages in Avionics and Defense applications

36V Battery voltage used on some electric golf carts, electric scooters, electric bikes, high power cordless tools etc..

42.4V Voltages must be less than or equal to 42.4V peak/60V dc to meet safe limits and to be SELV.

42.4V Hazardous Voltage is a voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.(IEC 60950)

48V Battery backed up -48V voltage is used on telecom systems for powering telephone exhanges and other telco equipment. The normal service voltage range for the -48 Vdc nominal supply at interface “A” shall be -40,5 Vdc to -57,0 Vdc according to ETSI EN 300 132-2

48V Some data centers use 48V DC to power servers (battery backup easy)

48V Phantom power feed for microphones in audio mixers most often uses +48V phantom power voltage
48V some automation systems use +48V power for equipment and I/O (electrical power distribution)

50V Work on energized circuits or apparatus below that voltage requires no “Hazard/Risk Evaluation.”     NFPA 7OE

60V Voltages must be less than or equal to 42.4V peak/60V dc to meet safe limits and to be SELV.

60V Hazardous Voltage is a voltage exceeding 42.4V peak or 60V d.c., existing in a circuit which does not meet the requirements for either a Limited Current Circuit or a TNV Circuit.(IEC 60950)

72V standard input voltage in rail applications

75V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c

110V Seen on electrical power distribution control automation as IO voltage and for operating actuators on high voltage power distribution stations.

110V standard input voltage in rail applications

120V Extra-low voltage high limit is 120 V ripple-free d.c.

125V Commonly used insulation resistance testing voltage used for low voltage wiring testing where 250V test voltage is too much.

160V The highest DC voltage covered by the telephone/telecom/ITE industry is 160V (ANSI T1.311)

169V The peak voltage on 120V AC mains power is around 169V, you get around this voltage if you rectify and filter 120V mains power

220V Seen on electrical power distribution control automation as IO voltage and for operating actuators on high voltage power distribution stations.

250V Commonly used insulation resistance testing voltage. Tests on SELV and PELV circuits are carried out at 250 V.

270V common standard input voltages in Avionics and Defense applications

324V The peak voltage on 230V AC mains power is around 324V, you get around this voltage if you rectify and filter 230V mains power

380V DC power voltage for DC feed used on some data centers. Emerge Alliance pushes using this 380V system.

500V Commonly used insulation resistance testing voltage. Insulation tests at normal mains wiring (230V) is commonly tested with 500V test voltage. Minimum insulation resistance expected on mains circuit is 0.5 Mohm. Also test between SELV and PELV circuits and the live conductors of other circuits must be made at 500 V.

575V DC power voltage for DC feed used on some data centers

600V Voltage used on third rail powered locomotive systems and overhead lines for older trams

750V Voltage used to power trains in Helsinki subway (third rail powering) and also used in modern tram systems

1000V Commonly used insulation resistance testing voltage for circuits that operate above 500 V up to 1000 V.

1500V Low Voltage Directive is effective for voltages in range 50 – 1000 volts a.c. or between 75 and 1500 volts d.c

2500V Commonly used insulation resistance testing voltage

3250V Use 2300V rms or 3250V dc test voltage for dielectric-withstand test for double insulation

5000V Commonly used insulation resistance testing voltage when testing high voltage wiring


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  3. 24V Batteries Dekcell says:

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    [...]Common DC voltage levels « Tomi Engdahl’s ePanorama blog[...]…

  4. Teardown: Relay DIN rail base « Tomi Engdahl’s ePanorama blog says:

    [...] As you can see in the picture the whole product is designed for 48V DC operation. That 48V voltage level is used in telecommunications systems, on some data center applications and some a… [...]

  5. Tomi Engdahl says:

    Factory pre-configured with industry-standard voltages
    - ZSPM1511 output: 0.85 V
    - ZSPM1512 output: 1.0 V
    - ZSPM1513 output: 1.2 V

    “Many high performance field programmable gate array(FPGA), digital signal processor(DSP) and system-on-chip(SoC) applications require multiple supply voltages to power the FPGA, DSP, SoC, peripheral input/output devices and transceivers in the application,”


  6. Tomi Engdahl says:

    Power converters meet railway needs

    NAR150D DC/DC converters from Powerbox deliver 150 W of output power with typical efficiency of 93% for demanding railway applications. The dual-output units in the series are housed in slim 18.5-mm (0.73-in.) wide packages, allowing their use in tight, confined environments.

    Comprising a wide range of models, the ENAR150D series operates from inputs of 24 VDC (16.8 VDC to 30 VDC) or 110 VDC (77 VDC to 137.5 VDC) and provides two independent, isolated outputs of 12 VDC, 24 VDC, or 48 VDC.

    Able to meet the high-reliability requirements of the railway industry, the ENAR150D series achieves an MTBF of 500,000 hours at +45°C ambient. Converters provide a minimum technical lifetime of 15 years at +45°C and 80% load. Input-to-output isolation is 2100 VAC; output-to-case is 1000 VAC; and output-one-to-output-two is 500 VDC.

  7. Tomi Engdahl says:

    Home> Tools & Learning> Products> Product Brief
    Converters power automotive IoT designs

    ENA100 100-W and ENA200 200-W DC/DC converters from Powerbox are housed in IP21-rated plastic enclosures built for tough automotive applications

    The ENA100 and ENA200 series accept input voltages ranging from 10 V to 120 V (10 V to 18 V, 18 V to 32 V, 36 V to 75 V, and 55 V to 120 V). Output voltage choices include 12.5 V, 14.5 V, 24.5 V, and 28V.

  8. Tomi Engdahl says:

    AC/DC Power Supplies: Four Questions to Ask

    1. Can you connect the power supplies in parallel to provide higher output power or configure them to provide multi-phase or split phase outputs?

    2. What voltages and currents can I expect from modern power supplies?

    Voltage ranges have increased, particularly in military/avionics applications. Examples include:

    Standard avionics power plant simulation, which currently runs from 360 Hz to about 800 Hz.
    Simulation of next-generation avionics power plants already requires 1200 Hz and that will increase. Power at these frequencies is needed to test the electronics that will connected to those power plants.
    Torpedo alternator simulation, 3 kHz-4kHz, is needed to test the downstream power converters and electronics that will be connected to those alternators.

    Instead of the traditional 150 and 300 VAC ranges, the latest generation of AC/DC supplies now produce voltage ranges of 200 and 400 VAC, as well as DC voltages of 250 VDC and 500 VDC. These higher DC voltages come in handy in many applications. For example, MIL-STD-704, Test Method HDC302 requires voltage transients up to 475 VDC.

    3. I need to test my equipment at multiple ranges. What do I need?

    4. What features should I look for?
    Many of today’s AC/DC power sources have features that make testing easier and more effective. These include touchscreen displays dashboards and control panels where you can save your GPIB address or set your RS-232 parameters, or set up your LAN connection.

  9. Tomi Engdahl says:

    EN50155 Compliance to Railway Standards

    The specification is surprisingly relaxed compared to the typical industrial operating range requirements of -40°C to +85°C, as only the highest specification of TX rated parts need to cover this ambient temperature range for just 10 minutes during start up conditions.

    Conversely, the shock and vibration requirements are anything but benign, as one would expect in such a hostile environment as rolling stock. The requirements are detailed enough to warrant the calling up of a separate standard, EN 61373: Railway Applications – Rolling stock equipment

    The next section in the EN50155 standard covers the power supply requirements. The nominal input voltages are 24, 48, 72, 96 and 110VDC, of which 24, 48 and 110 are the most commonly used. Although not covered in the standard, 36V is also often requested.

    The standard defines the continuous input voltage range as being between 0.7 and 1.25 nominal, with short-term fluctuations between 0.6 and 1.4 being allowed. In practice, power supplies must work continuously between 0.6 and 1.4 nominal as no “deviation of function” is tolerated.

    A basic rule-of-thumb for DC/DC converter design is that a 4:1 input voltage range is the practical limit for most typical designs. Thus all of the nominal input voltages can be covered by just three standard converters

    An extreme example of the layered approach of EN50155 is the section in the standard regarding EMC, surges, ESD and transients. The standard covers these points in just two short sentences by referring to another standard called EN50121-3-2: Railway Applications – Electromagnetic compatibility Part 3-2: Rolling Stock – Apparatus.

    The last section of EN50155 sets out a useful checklist of all of the mandatory or optional type approval tests, along with a description of how to carry out the test or a reference to another standard which defines the test and pass/fail criteria.

  10. Tomi Engdahl says:

    The 5 Big EN50155 Compliance Requirements for Railway Applications

    Power Supply Input Voltage: EN50155 requires minimum voltages of 24, 48, 72, 96 and 110V DC. Power supplies utilized for railway applications must operate within 0.6 and 1.4 nominal with no deviation. This is to ensure that every railcar can functionally operate. It is also advantageous to implement an input capacitor, which will help to level out any ripple voltage, creating more DC input consistency.

  11. Tomi Engdahl says:

    The Next Opportunity for Utility PV Cost Reductions: 1,500 Volts DC

    The average cost for a 20-megawatt fixed-tilt utility PV project in the U.S. in 2015 is just above $1.50 per watt — relatively cheap in historical terms. However, with record-low PPAs being signed at these levels, even subtle changes in component costs can kill projects.

    The most immediate opportunity that we see for utility-scale PV system cost reduction is the installation of 1,500 Vdc systems. Higher-voltage systems enable longer strings, which allow for fewer combiner boxes, less wiring and trenching, and therefore less labor. According to our research, installing 1,500 Vdc systems in place of now-standard 1,000 Vdc can lower costs by as much as $0.05 per watt.

    Déjà vu: The history of higher-voltage PV

    If this conversation seems familiar, it’s because we’ve had it before. Prior to 2013, most systems in the United States were installed at 600 Vdc, while systems in Europe were installed at 1,000 Vdc. This enabled lower system costs in Europe, while installers in the U.S. were kept at low voltages by UL testing limitations and the National Electric Code, which limited voltage to 600 Vdc due to a broadly interpreted revision added in 1999.

    In 2013, however, many authorities began allowing 1,000 Vdc systems for commercial and projects, and UL standards evolved to enable this.

    From an installation perspective, the shift to 1,500 Vdc has similar benefits and regulatory barriers to the 1,000 Vdc transition.

    The beginnings of 1,500 Vdc

    When 1,000 Vdc systems became prevalent in the United States, there was already widespread availability of products from Europe, and thus the testing standards were the main barrier. Testing standards are also a barrier to 1,500 Vdc, but 1,000 Vdc is still the standard voltage in Europe, and so there is also exceptionally limited availability of 1,500 Vdc products.

    This doesn’t mean Europe didn’t lead the U.S. again with 1,500 Vdc. Europe’s electrical standards body, the International Electrotechnical Commission (IEC), considers 1,500 Vdc the low-voltage limit and enables certification to that voltage.

    As a result of these industry efforts, 1,500 Vdc parts are now commercially available for every system component. But module manufacturers are limited by the existing standards landscape.

    Product availability has been the primary barrier to 1,500 Vdc in Europe, but product introductions have been hampered by standards in the United States. Nobody wants to introduce a product that is unable to be used in the U.S. market. UL 1703, the gold standard for PV modules, currently only enables module testing to 1,000 Vdc.

    We expect all standards issues for 1,500 Vdc to be resolved in the next two years.

    As these regulatory barriers dissolve, manufacturers will begin to introduce 1,500 Vdc products in volume. We expect this to begin in mid-2015 and continue into 2016.

    1500 VDC Collection Systems

  12. Tomi Engdahl says:

    1,500 Vdc Utilization Voltages in Ground-Mount Applications

    EPCs in Europe pioneered 1,500 V plant architectures, just as they were first to market with 1,000 V PV systems. Belectric, for example, is an international solar project developer headquartered in Germany, with a long history of innovation and market firsts such as the construction of the first thin-film PV system in Europe (2001). According to a company press release, in June 2012 Belectric constructed and commissioned the world’s first utility-interactive 1,500 Vdc solar power plant. Power Conversion, a Berlin-based division of GE Energy, supplied the liquid-cooled inverters used to connect the 1,500 Vdc system to the utility grid.

    In conjunction with GE Power Conversion, First Solar began publicly touting the benefits of 1,500 Vdc solar arrays in early 2014.

    When you consider the broader development and deployment of 1,500 Vdc systems, the rest of the utility-scale solar industry is not far behind First Solar’s lead. At the risk of oversimplification, 2015 was most notable for the widespread release of 1,500 Vdc–rated components—modules, inverters, combiners, fuses and so forth—certified to UL standards. In 2016, a second wave of large-scale project developers, including Recurrent Energy, began selectively deploying 1,500 Vdc PV systems as a way of testing the waters and building a knowledge base for the widespread adoption of 1,500 Vdc systems in 2017.

    According to 1,500-Volt PV Systems and Components 2016–2020 (see Resources), a GTM Research report, 1,500 Vdc systems will account for 4.6 GW of global utility-scale solar installations in 2016. Though GTM Research analysts estimate that the US market will account for roughly 60% of the 1,500 Vdc field deployments worldwide in 2016, they expect that demand in the rest of the world will dwarf that in North America from 2017 forward. In other words, once early adopters have proven the technology benefits in the field, analysts expect to see a steady transition from 1,000 Vdc to 1,500 Vdc.

  13. Tomi Engdahl says:

    Getting ready for a lower-power future: the keys to successful adoption of new low-voltage memory ICs

    Today, the circuitry on the board in mainstream industrial and consumer products operates from a wide range of supply voltages: the power rails are most commonly at 5V, 3V, 2.5V, 1.8V and various lower voltages. To ensure compatibility between devices from different manufacturers, and to avoid unnecessarily complicating board-level power system design, merchant semiconductor manufacturers typically design their standard products to run from one or more of these standard power rails. But there is a strong force resisting this general preference for stability and compatibility. It can be summed up in one word: mobility.

    So every milliwatt saved from the power budget is important to product designers. And for them, the industry’s use of power rails at various standard voltages, often at 1.8V or higher, is a problem, not an advantage: that is because many components – particularly those operating in the digital domain – would with some modification be quite capable of operating from a power rail at a voltage lower than 1.8V, resulting in valuable savings in active and stand-by power consumption.

    Clear direction of travel
    Today, system designers typically have to provide multiple power rails in order to accommodate components operating from different supply voltages. Analogue devices such as sensors commonly have a 3V or — in industrial applications — even a 5V supply. Legacy digital components might have a 3.3V, 2.5V or 1.8V supply. At the low end of the voltage range, the latest applications processors or systems-on-chip built on advanced process nodes, such as 28nm or smaller, might have a core operating voltage as low as 1.0V.

    Figure 1 shows how DRAM technologies have led the memory IC industry beyond 1.8V. Standard DDR2 DRAM was the last to use a 1.8V supply. After that, successive generations of DDR DRAM operated at 1.5V (DDR3), then 1.37V (DDR3L) before reaching today’s level, 1.2V (DDR4).

    Figure 1 also shows in green the supply requirements of successive families of NOR Flash ICs from Winbond, operating at the standard 3V, 2.5V and 1.8V levels. Now the latest NOR Flash families offer two voltage ranges: one at 1.2V, and another with an extended voltage range nominally at 1.5V.

    In supporting the 1.2V voltage and the extended 1.5V level with its newest generation of NOR Flash ICs, Winbond is seeking to harmonise its product offerings with the broader semiconductor industry.

    Feature set compatible with 1.8V devices
    Winbond has designed the new 1.2V series and extended 1.5V series to match the existing 1.8V devices.

    Momentum behind 1.2V and extended 1.5V power rails
    Winbond has decided to be first to market in the serial Flash sector with 1.2V and extended 1.5V devices to give early momentum to a trend that seems certain to gain speed as manufacturers of battery-powered devices look for further savings in power consumption.

    These 1.2V products have been designed in and endorsed by new chipset companies working in the low power area like Espressif

    As a result, the Flash market is ready to standardise on 1.2V and extended 1.5V as the next power node below 1.8V,

  14. Tomi Engdahl says:

    What’s Ahead for the Venerable 12-V Automotive Battery?

    To improve fuel efficiency, 48-V systems are supplementing 12-V batteries, especially in the emerging world of mild hybrids.

    Many pundits believe that given the greater proliferation of more electronics in modern automobiles with each new model year, the decades-old, sealed lead-acid (SLA) 12-V car battery is being strapped to handle automotive power demands. Not only are more infotainment and safety electronic features being added every year, but when you include stricture emission and fuel-economy requirements, one can surmise that even the most efficient SLA battery in use today needs some help.

    That said, the 12-V battery is here to stay, at least for the near term—i.e., the next few years. But it has its many drawbacks, including the fact that the lead element is hardly in vogue ecologically. And except for a few applications that need its heavy weight, the heavier higher-voltage batteries like 24 V or 36 V just weigh down the car further.

    That said, the 12-V battery is here to stay, at least for the near term—i.e., the next few years.

    And except for a few applications that need its heavy weight, the heavier higher-voltage batteries like 24 V or 36 V just weigh down the car further.

    In fact, a 42-V auto battery system was proposed in the late 1990s in favor of 48 V to supplement the 12-V battery for automotive electrical power. The 48-V approach was deemed optimal in terms of fuel-efficiency savings, helping auto manufacturers meet emissions standards, and providing more power for the growing number of features desired by drivers to propel electric motors and electronic systems.

    The 48-V supplement to a 12-V battery has been demonstrated to be a better approach by Controlled Power Technologies

    In 2011, several German auto manufacturers introduced cars with on-board 48-V systems known as mild hybrids. This mild 48-V electrical system is emerging as the next revolution in cars.

    At a weight of 8 kg (17.6 lbs), the mild hybrid is not much heavier than existing 12-V batteries, and it is comparatively smaller

    The demand for mild-hybrid Li-ion 48-V batteries is rapidly growing, particularly in Europe and Asia, according to an IHS study. Automotive experts believe that by 2025, one fifth of all cars sold around the worldwide will have some sort of 48-V technology for power.

  15. Tomi Engdahl says:


    48 Battery, Telecom, Automation, Data Centers, Microphones
    60 Hazardous voltage (42.4V Peak or 60V DC) (UL, IEC, CSA)
    72 Rail
    110 Power Distribution Control, Rail
    160 Highest DC Voltage Covered by Telephone/Telecom/ITE Industry
    170 Rectified 120V AC Mains
    220 Power Distribution Control
    270 Avionics, Defense
    340 Rectified 240V AC Mains
    96-375 Electric Vehicles
    380-575 Telecom, Data Centers
    200-600 Grid Tie Solar
    680 Rectified 480V AC Mains

  16. Tomi Engdahl says:

    Voltage Values

    In the following, “voltage” means the voltage between the conductors. The standard voltage values used are:

    1. Extra low voltage (ELV) – means any voltage not exceeding 50V a.c. or 120V ripple free d.c.
    2. Low voltage – means any voltage exceeding 50V a.c. or 120V ripple free d.c. but not exceeding 1kV a.c. or 1.5kV d.c.
    3. High voltage (HV) – means and voltage exceeding 1kV a.c. or 1.5kV d.c.
    4. Extra high voltage (EHV) means any voltage exceeding 220kV.

  17. Tomi Engdahl says:

    +270 VDC input per Mil-Std 704F

  18. Tomi Engdahl says:


    DC normal operation characteristics

    28 Volt DC system
    22.0 to 29.0 Volts

    270 Volt DC system
    250.0 to 280.0 Volts

  19. Tomi Engdahl says:

    Coaxial power connector

    A coaxial power connector is an electrical power connector used for attaching extra-low voltage devices such as consumer electronics to external electricity. Also known as barrel connectors, concentric barrel connectors or tip connectors, these small cylindrical connectors come in an enormous variety of sizes.

    There are many different sizes of coaxial power connectors

    Contact ratings commonly vary from unspecified up to 5 amperes (11 amperes for special high-power versions). Voltage is often unspecified, but may be up to 48V with 12V typical.

    The sizes and shapes of connectors do not consistently correspond to the same power specifications across manufacturers and models.

    Generic plugs are often described by their inside diameter, such as 2.1mm DC plugs and 2.5mm DC (direct current) plugs. 5.5mm OD plugs

    next-most common size is 3.5mm OD with a 1.3mm ID

    There are several standards in existence, such as IEC, EIAJ in Japan and DIN in Germany.

  20. Tomi Engdahl says:

    High-Voltage Vehicle Systems Are Here To Stay


    As electrification takes over automotive design, efficiency becomes crucial, which has reignited interest in the dual-system approach using

    12 V and 48 V.

    The auto industry is rapidly moving toward what might be called “total vehicle electrification,” in which everything that can be powered by

    electricity rather than hydraulics or belts will undergo that transformation. Very simply, engine-driven components powered by electricity

    reduce the load on the engine, fuel consumption, and thus emissions.

    In addition, the increasing number of electronic systems, such as ADAS, employed in vehicles creates higher demand for power. As a result,

    the auto industry intends to supplement current 12-V power with a separate 48-V system, each one dedicated to specific needs.

  21. Tomi Engdahl says:

    The Thin Line Between Safety and Death on the London Underground | The Tube | Spark

    Third-rail current collectors

  22. Alan Muller says:

    I would add 32 volts which was/is a common marine voltage and also used for freestanding rural electric systems. 32 volt systems are no longer common but not entirely extinct.

  23. Tomi Engdahl says:

    12 vs 24 Volt Solar Systems

    Which voltage should you choose for your house? Here’s what you need to consider when choosing between 12 and 24 volt systems.

  24. Tomi Engdahl says:

    EEVblog #1015 – Beware Evil (But Clever) DC Jacks!

    Trivia time. Dave explains one of the reasons why annoying centre negative DC power jacks exist.


    Nice video. I always thought it was a Japanese thing.

    I’m scratching my head at why the pass through being on the sleeve is a reason for making the sleeve positive. It works just as well negative. I do it all the time, battery negative on the pass through, disconnects battery when plug is inserted just the same.

    Either way one end of the battery is floating, so who cares where exactly it’s floating.

  25. Tomi Engdahl says:

    750-V DC Input Railway Converter Delivers High Conversion Efficiency
    ABSOPULSE’s HVI 41R-F1 converter incorporates an input surge withstand capacity of 1300 V dc.

    The HVI 41R-F1 converter operates from 750 V dc (525 V to 975 V dc), the traction voltage required for mass transit vehicles including trams, metros and light rail, mining locomotives, and trolleybuses. It also incorporates an input surge withstand capacity of 1300 V dc. The unit delivers a regulated output of 24 V dc/2 A.

    The converter is designed for an operating life of up to 30 years. The elimination of optocouplers from the feedback loop contributes to significantly lower component count and higher MTBF compared with conventional designs, according to ABSOPULSE. The design is verified for 5600-V dc input-to-output isolation. Production level testing is 5000-V dc input-to-output. Other electronic protection includes inrush current limiting, reverse-polarity protection, and output current limiting with short-circuit protection.

    The HVI 41R-F1 meets the requirements of EN 50155 for electronic equipment used on rolling stock, including EN 61000-4-2, EN 61000-4-3, EN 61000-4-4, and EN 61000-4-6 standards. Heavy filtering on the input and output ensures compliance with EN 50121-3-2.

    The 50-W converter is cooled by conduction via baseplate.

  26. Tomi Engdahl says:

    International Standard IEC 60038:1983 defines a set of standard voltages for use in low voltage and high voltage AC electricity supply systems.
    According to it anything anone 1000V AC and 1500V DC is high voltage.
    Extra low voltage is below 50V AC and 120V DC.

  27. Tomi Engdahl says:

    Telecom sites typically have a battery backed up -48 VDC Power Supply in them. It was originally designed to power PSTN central office equipment, and since used to power very many other telecom and networking equipment.

    Battery backed up is also used with telecontrol RTUs:
    Sure, you might have commercial AC available at a remote site, but what happens during an outage?

    That’s the moment when your protected DC power plant (commonly -48, +24, or +12 VDC) comes into its own. If your RTU is powered by that DC power source (ideally a redundant power input setup, with one input fed by the rectifier and another by the battery string), it will continue to operate during the times when you need it the most.

  28. Tomi Engdahl says:

    Wide variety of input versions are suitable for 12V and 24V automotive vehicles, 48V, 72V and 96V industrial vehicles as well as 28V defense, avionics and marine systems, not forgetting most railway systems from 24V up to 110V.


  29. Tomi Engdahl says:

    Why does the aerospace industry use a 28V DC power supply?

    What you are observing is not really a physical difference, it’s just different conventions for defining the system. The aircraft in question do use 24-volt batteries. They use 28-volt generators, though. We want the generator to produce excess voltage that can be used to keep the battery charged. Similarly, for a 12-volt battery, a 14-volt generator would be typical.

    Aviation tends to define the system based on generator voltage while other industries, such as automotive, tend to define the system based on battery voltage. Your 12-volt car battery is probably connected to an alternator putting out 14-volts.

    As for why 28-volt instead of 14-volt – there are a few reasons. One is that higher voltage means smaller wires can be used, saving weight and thus fuel. Another is that during early days, someone came up with a really good and light 28-volt generator that worked well with other aviation equipment and it became common and then a standard,

  30. Tomi Engdahl says:

    Lucid said it is able to hit this benchmark because the vehicle has a 900-volt electrical architecture when combined with its lithium-ion cells, battery and thermal management system and powertrain efficiency. Most electric vehicles — with the exception of the Porsche Taycan and future Kia EVs — have a 400-volt architecture.

  31. Tomi Engdahl says:

    The Surging Need for Power Density in Railway Systems

    Electrical Traction Systems

    Track electrification is the type of source supply system used while powering all electric locomotive systems. This can be ac or dc, or even a composite supply.

    There are three main forms of electric traction systems:

    Direct-current (dc) electrification system
    Alternating-current (ac) electrification system
    Composite system

    Direct current can vary with 300, 500, 600, 750, 1200, 1500, and 3000 V dc.
    Alternating current varies with 15 kV ac @16.7 Hz or 25 kV ac @50/60 Hz.
    And there’s a composite system with 1.5 kV dc, 3 kV ac @16.7 Hz, or 25 kV ac @ 50 Hz

  32. Tomi Engdahl says:

    The dc supply can be supplied to the train vehicle in two ways:

    3rd and 4th rail systems that are operated at low voltages (600 to 1200 V).
    Overhead wire rail systems that have high voltages (1500 to 3000 V).

    DC electrification supply systems include:

    300- to 500-V supply for special systems such as battery systems.
    600 to 1200 V are for urban railways such as tramways and light metro trains.
    1500 to 3000 V are for suburban and mainline services such as light metros as well as heavy metro trains.

  33. Tomi Engdahl says:

    What’s Driving EVs to Higher Battery Voltages?
    Aug. 30, 2022
    Electric-vehicle makers are turning to 800-V systems to solve range and charging time issues that have created barriers with consumers and slowed the rollout of EVs. Here’s how they work.|7211D2691390C9R&oly_enc_id=7211D2691390C9R

    What you’ll learn:

    Design considerations for the power solution in an 800-V system.
    How an 800-V bus system impacts EV design.
    How 800 V enables reduced charging time.
    How InnoSwitch3-AQ ICs deliver solutions for 400-, 600-, and 800-V EV designs.

    Many countries are enacting legislation to increase the number of electric vehicles (EVs), with the goal of phasing out or eventually banning petrol and diesel vehicles. While early adopters may have been motivated by environmental benefits, a sizable portion of the market also remains concerned with range limitations and charging times of EVs.

    The automotive industry is being challenged to innovate and create solutions that appeal to a larger audience, which is driving the trend to higher battery voltages. Most of the passenger EVs on the road today run using 400-V batteries. EV buses and trucks are 600-V-class vehicles, and 800 V is starting to be adopted for passenger vehicles.

    The introduction of 800-V systems, a significant step up from existing 400-V systems, is happening faster than many predicted. What are the benefits of an 800-V system, and how do they help solve some of the problems that have been barriers to consumers and slowed the rollout of electric vehicles?

  34. Tomi Engdahl says:

    What’s Driving EVs to Higher Battery Voltages?
    Aug. 30, 2022
    Electric-vehicle makers are turning to 800-V systems to solve range and charging time issues that have created barriers with consumers and slowed the rollout of EVs. Here’s how they work.|7211D2691390C9R&oly_enc_id=7211D2691390C9R

    What you’ll learn:

    Design considerations for the power solution in an 800-V system.
    How an 800-V bus system impacts EV design.
    How 800 V enables reduced charging time.
    How InnoSwitch3-AQ ICs deliver solutions for 400-, 600-, and 800-V EV designs.

    The automotive industry is being challenged to innovate and create solutions that appeal to a larger audience, which is driving the trend to higher battery voltages. Most of the passenger EVs on the road today run using 400-V batteries. EV buses and trucks are 600-V-class vehicles, and 800 V is starting to be adopted for passenger vehicles.

    The introduction of 800-V systems, a significant step up from existing 400-V systems, is happening faster than many predicted.

    Motion relies on the interaction of the rotor magnetic field and a rotating magnetic field generated by time-controlled currents in the stator windings. As the motor operating voltage increases for a given input power, it reduces the input RMS current and, therefore, the stator winding copper losses. Losses are typically reduced by a factor of 4 using an 800- versus a 400-V supply.

    This offers the opportunity to reduce the copper winding wire diameter, which decreases the overall volume as well as increases the packing efficiency, allowing for smaller motors. The same lower current requirements in an 800-V system reduce not just the motor copper losses, but loss in the entire system wiring loom, introducing weight, space, and cost savings.

    Typically, 800-V systems also move from silicon-based IGBTs to silicon-carbide (SiC) MOSFETs. SiC devices provide much higher switching speeds and thus lower switching losses. As a result, the operating frequency will increase, which further reduces motor losses due to reduced harmonic currents.

    Lower weight improves handling and acceleration, valuable in the high-end sports car market. Together with reduced losses, it improves range, which directly relates to battery and therefore vehicle cost. Liberated space can be used to increase the size of the battery pack and, in turn, the range, or it can be allocated to increased passenger cabin space.

    800 V Enables Reduced Charging Time

    Charging time is a challenge for consumers, as well as commercial vehicles.

    How does an 800-V architecture help? As we have noted before, doubling the voltage cuts the current in half for the same power. During charging, heat dissipation is a limitation both for the charging cable and the vehicle charger inlet and internal wiring.

    Moving from 400 V to 800 V allows for doubling of the charging rate for the same losses. This has several benefits.

    Both Porsche and Kia have new all-electric vehicles whose range is starting to approach the median range for gas cars, and with charging times more comparable to refueling at a gas station with a quick stop to pick up supplies. The newest range of charging stations deployed have a 400-kW maximum rating, which is more than enough for the 800-V architecture.

    Porsche’s fully electric sports car, the Taycan, has a range of 420 km (260 miles). It uses the 800-V battery architecture and can charge from 5% to 80% in just 22.5 minutes on a fast-charging station at 300 A (240 kW). It’s still capable of using 400-V charging stations, which would take around 90 minutes. Kia announced its EV6 800-V-architecture car, which charges from 10% to 80% in just 18 minutes using a maximum power of 239 kW, with an extended range version that reaches 480 km (300 miles).

    800-V Adoption Has Been Faster than Expected

    The automotive market has adopted the 800-V architecture faster than was initially anticipated. Porsche led the way, but it’s not just sports cars—Kia and several China manufacturers now offer 800-V vehicles. As is typical for the automotive market, innovations start in the higher-end vehicles and slowly work their way down to the mass market as the technology becomes more affordable. The benefits offered by 800-V systems include cost savings that the mid-range consumer market can utilize much sooner than was first thought.

    As the automotive market embraces the 800-V architecture, we will undoubtedly see companies pushing the benefits of higher-voltage systems even further. These benefits scale up—thus, 900 V and beyond can increase these further, pushing range, weight, and charging times even more. The infrastructure will need to keep pace; the new 400-kW charging stations are already enabling this direction.

    Design Considerations for the Power Solution in an 800-V System

    High-voltage connected subsystems in an EV typically require a high- to low-voltage power supply. The increase to 800 V requires much higher isolation and voltage ratings.

    An EV battery pack consists of many individual cells connected in a series/parallel combination. Each individual cell operates over a voltage range of 3.1 to 4.2 V. For a nominal 800-V system, there are approximately 198 cells in series, giving an overall pack voltage of 610 to 835 V.

    An additional 20 to 30 V are typically added due to voltage rise during regenerative braking, giving a maximum voltage of 865 V. The power-supply internal switch must be rated significantly above this voltage. For a flyback converter, an additional 150 to 200 V must be added, giving a switch stress of 1065 V. Applying the usual 20% derating yields a specification of at least 1.33 kV.

    Another important design consideration is the need for a low-voltage startup, typically 30 to 40 V. The vehicle safety systems need to power-up first, to make sure all of the control electronics are operational before anything can start to move, or faults potentially occur. Designing a power supply that runs from 30 V to >900 V can be challenging.

  35. Tomi Engdahl says:

    Why do many laptops run on 19 volts?

    Now there’re laptops that use external power supplies rated at exactly 19 volts. That isn’t a multiple of anything suitable. Puzzles me a lot.

    The choice of 19 volts is because is it comfortably below 20 volts which is the maximum output voltage of power supplies that can be certified as LPS (Limited Power Source) with non-inherent power delivery limits.

    If you can keep at or below 20 volts, the whole safety certification thing becomes easier and cheaper.

    To make sure you’re within the limit accounting for manufacturing tolerances, go 5% lower, which is 19 volts. There you are. It has nothing to do with battery pack organization or LCD screens.

    This is not a design question as posed, but it has relevance to design of battery charging systems.


    The voltage is slightly more than a multiple of the fully charged voltage of a Lithium Ion battery—the type used in almost every modern laptop.

    Most laptops use Lithium Ion batteries.

    19 V provides a voltage which is suitable for use for charging up to 4 x Lithium Ion cells in series using a buck converter to drop the excess voltage efficiently.

    Various combinations of series and parallel cells can be accommodated.

    Voltages slightly below 19 V can be used but 19 V is a useful standard voltage that will meet most eventualities.

    A Lithium Ion cell has a maximum charging voltage of 4.2 V (4.3 V for the brave and foolhardy). To charge a 4.2 V cell at least slightly more voltage is required to provide some “headroom” to allow charge control electronics to function. At the very least about 0.1 V extra might do but usually at least 0.5 V would be useful and more might be used.

    One cell = 4.2 V
    Two cells = 8.4 V
    Three cells = 12.6 V
    Four cells = 16.8 V
    Five cells = 21 V.

    I have seen laptop batteries with

    3 cells in series (3S),
    4 cells in series (4S),
    6 cells in 2 parallel strings of 3 (2P3S),
    8 cells in 2 parallel strings of 4 (2P4S)

    and with a source voltage of 19 V it would be possible to charge 1, 2, 3 or 4 LiIon cells in series and any number of parallel strings of these.

    For cells at 16.8 V leave a headroom of (19−16.8) = 2.4 volt for the electronics.

    With say 0.7 V of headroom it would notionally be possible to use say 16.8 V + 0.5 V = 17.5 V from the power supply—but using 19 V ensures that there is enough for any eventuality and the excess is not wasted as the buck converter converts the voltage down as required.

    When a Lithium Ion cell is close to fully discharged it’s terminal voltage is about 3 V. How low they are allowed to discharge to is subject to technical considerations related to longevity and capacity. At 3 V/cell 1/2/3/4 cells have a terminal voltage of 3/6/9/12 volt. The buck converter accommodates this reduced voltage to maintain charging efficiency. A good buck converter design can exceed 95 % efficient and in this sort of application should never be under 90 % efficient (although some may be).

    I recently replaced a netbook battery with 4 cells with an extended capacity version with 6 cells. The 4 cells version operated in 4S configuration and the 6 cell version in 2P3S. Despite the lower voltage of the new battery the charging circuitry accommodated the change, recognising the battery and adjusting accordingly. Making this sort of change in a system NOT designed to accommodate a lower voltage battery could be injurious to the health of the battery, the equipment and the user.

    This is not a design question as posed, but it has relevance to design of battery charging systems.


    The voltage is slightly more than a multiple of the fully charged voltage of a Lithium Ion battery—the type used in almost every modern laptop.

    Most laptops use Lithium Ion batteries.

    19 V provides a voltage which is suitable for use for charging up to 4 x Lithium Ion cells in series using a buck converter to drop the excess voltage efficiently.

    Various combinations of series and parallel cells can be accommodated.

    Voltages slightly below 19 V can be used but 19 V is a useful standard voltage that will meet most eventualities.

    Almost all modern laptops use Lithium Ion (LiIon) batteries. Each battery consists of at least a number of LiIon cells in a series ‘string’ and may consist of a number of parallel combinations of several series strings.

    THis is an excellent “reverse” engineering design question.

    All mobile computers may use similar down-converter dc-dc battery charger philosophy yet have may use different chips and profiles., which are managed by the laptop, not the external charger. Often a wider range of charger voltages with more capacity can be used, because of the ability inside to step down a range of inputs often wider than specified. Extreme ranges may reduce efficiencies and increase max power during dead charge while display is on full brightness. The backlight is the biggest steady draw and the CPU/GPU have the biggest peaks for high performance use. (i7 quad cores etc)

    Universal Battery chargers.
    I purchased a Universal charger during a long road trip. I later chose to use it to drive 60 Watts of LED’s. The charger was spec’d @15~24V, 63W max. It had a 6 pin header just before the interchangeable coaxial power plugs. One of the pins was a remote sense line for plug voltage to compensate for DC line loss. I characterized the input and found it could be used to regulate the output from 5~50V with a 2.5V input control range centered around 3V. I used a Log Pot, a few resistors an LED and a cap to control this custom dimmer from 10 to 100% using al the available power and my wife was very happy with LED sunshine over the bay window with glare proof black egg crating. It was around 3x brighter than direct sunlight on max.

    In any case every mobile computer has to regulate the external supply so the exact voltage is not that critical and you can get away with a wider range. The lower the input voltage , the higher the current and visa versa , it should work but efficiency may vary over the range.

    Most mobiles tend to run in lower cell voltages to reduce ESR of the pack which affects voltage drop under load and cross regulation ripple from propagating to further regulators which step-down and step up on-board for internal CPU/ I/O and peripherals e.g. 5 & 12V.

    Bigger mobile PC packs include;

    9 cell= 10.1V (3P3S) 10 cell= 7.4V (5P2S) 12 cell= 14.8 (3P4S)

    Useful Factoid: You can run a mobile computer with NO battery installed as that Battery management regulator is simply not used to run the internal DC-DC regulators. This serves to reduce heat loading on old laptops and reduces battery heat aging even if they stay @100% without drain. (But you will shutdown on a power glitch.)

    You can use also get away with a larger power charger with adequate voltage to step down to the battery voltage and it should not affect performance much on efficiency as long as there is adequate power in.

    Factor in all that and with the commonly used 4 lithium batteries in series for “larger” or longer running on batteries laptops and you end up needing a nominal 19VDC external power supply which actually could be any where from about 17 – 20 VDC. The internal DC/DC converters for generating the lower DC voltages and the the battery charging circuitry easily accepts that range plus probably another few more volts.

    BTW, the 19VDC is also needed to get watt-hours up for longer run times and the current down in the larger laptops because the ubiquitous barrel connector is only rated to handle 5A – and that is for a really good one. Most are 2-3A. That is the main reason you do not want to be plugging and unplugging that connector when your PC is powered on as you’ll burn the contacts eventually making for unreliable contact in that connector.

    To learn more about PC connectors, see:


    The 19 volts is to charge the battery pack which has multiple Li-ion cells in series. The laptop internal electronics are powered by a switching regulator from the battery voltage and/or the 19 volts from the AC adapter. This gives a decent run-time for the laptop as the battery voltage drops from discharge during use. This is the ONLY reason for 19 volts. It has NOTHING to do with the actual laptop internals, except the internal switching regulated power supply which adapts to the changing battery voltage, and provides constant, regulated voltages to internal systems (CPU, ram, hard disk, etc.)

  36. Tomi Engdahl says:

    Bridging 12 V and 48 V in dual-battery automotive systems
    How a bidirectional buck-boost controller helps support a dual-bus topology

    Bridging 12 V and 48 V in dual-battery automotive systems2November 2018
    The 12 V lead-acid battery system has met its
    match. With increasingly strict emission regulations,
    growing power load requirements of advanced
    automotive electronics and the conversion from
    mechanical components to electronic functions,
    the traditional automotive battery of choice has
    reached its current-carrying capacity.
    In response, automakers and their suppliers have developed a second, additional
    electrical system at 48 V which delivers more power at lower currents than a traditional
    12 V battery can produce alone.

    The new configuration consists of two separate
    branches. The traditional 12 V bus uses a
    conventional lead-acid battery for customary loads
    such as infotainment, lighting and windows; while
    the new 48 V system can support heavier loads
    such as starter generator units, air-conditioning
    compressors, active chassis systems, electric
    superchargers, turbochargers and
    regenerative braking.

    The 48 V system saves weight in the wiring harness.
    A higher voltage allows for smaller wire gauge,
    which reduces cable size and weight without
    sacrificing performance; today’s high-end vehicles
    can have more than 4 km of wiring

    Along with the traditional 12 V battery, a 48 V
    lithium-ion battery or a supercapacitor and a
    bidirectional DC/DC converter round out the
    dual-battery system to deliver up to 10 kW of
    available power. Bidirectional power transfer is
    required to charge either battery if it’s discharged
    and to provide extra power for the opposite
    voltage rail in an overload condition.

  37. Tomi Engdahl says:

    Which is More Dangerous? Phantom Power, USB Power or a 9 Volt Battery?

    I will test to see which makes more noise with a speaker, which lights and LED brighter, can melt small wires, is louder when connected to a mic and which tastes the best.

    00:00 Introduction
    00:59 What is Phantom
    01:27 USB Power
    01:55 9 volt battery
    02:07 LED Test
    04:44 Touch Test
    05:22 Speaker Test
    08:06 Wire Short
    10:47 Wired Wrong Into a Mic
    13:07 Eye and Lick Test
    15:35 Summary

  38. Tomi Engdahl says:

    Tesla Confirms The Switch To 48 Volt System
    The Tesla Cybertruck will get it first.

    Tesla moves forward with applying improvements to the low-voltage system of its electric vehicles, which so far was operating at roughly 12 volts just like in the vast majority of other cars.

    During the recent 2023 Investor Day, Tesla’s representatives confirmed the intention to introduce a 48V system, which despite many years, is still a rare solution in the automotive industry.

    The first step for Tesla was the switch from 12V lead-acid auxiliary batteries to 12V lithium-ion auxiliary batteries, announced in February 2021, and initially launched in the refreshed Tesla Model S/Model X (starting with the Plaid) – see an in-depth teardown here – and later used also in the Model 3/Model Y (in late 2021).

    According to Tesla, the old lead-acid batteries were a major source of failures in Tesla cars, and they needed a replacement about every four years or so. The new lithium-ion batteries are expected to withstand the lifetime of the car (just like the main traction battery)

    Tesla says that starting with the Cybertruck (this year), the Optiums robot, and all future electric vehicles, the 48V low-voltage system will be used.

    For reference, the automotive industry moved from 6V to 12V in the 1960s (currently smaller vehicles might still use 6V, while larger vehicles use 24V).

    Tesla will use a 48V system because it will reduce the current by a factor of four, compared to 12V systems. This voltage level is still considered safe.

    The increase in voltage is a necessity as power demand for onboard electrical devices steadily increases and at 12V, the wires are becoming thick, heavy, and costly.

    With a 48V system, there will be noticeable weight and cost savings, while at the same time, efficiency might increase.

  39. Tomi Engdahl says:

    Simuloi jo nyt tulevia 800 voltin sähköautoakustoja

    Sähköautojen arkkitehtuureissa on käynnistymässä siirtyminen 400 voltin järjestelmistä 800-volttiisiin. Englantilainen Pickering Interfaces on esitellyt PXI-pohjaisen simulaattorijärjestelmän, jolla näitä akustoja ja niiden voidaan emuloida.

    Pickering päivitti 41/43-752A-akkusimulaattorivalikoimansa viime viikolla. Uudet moduulit ovat ihanteellisia sähköajoneuvojen akuston emulointiin BMS-testisovelluksissa. Jännite-eristys on nostettu 1000 volttiin, jotta voidaan emuloida 800 voltin akustoja.

    Pickeringin simulaatiotuotepäällikkö Paul Bovingdonin mukaan suurimman osan sähköautoteollisuudesta odotetaan siirtyvän 400 V:sta 800 V:n arkkitehtuureihin vuoteen 2025 mennessä. Tämä tarkoittaa huomattavasti nopeampia latauksia.

  40. Tomi Engdahl says:

    48-V Systems: What You Need to Know as Automakers Say Goodbye to 12 V
    July 21, 2023
    Today, 48-V power systems are already helping improve the efficiency and performance of ICE and mild hybrid vehicles, but they will become an essential technology for tomorrow’s EVs.|7211D2691390C9R&oly_enc_id=7211D2691390C9R


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