Power supply electronics

A power supply unit (PSU) is an electronic circuit that converts device input voltage fed to the device being powered to the voltage or voltages needed internally by the electronics device. In typical computers a power supply unit (PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer.

Depending on the application the power supply can take in mains voltage (typically 110-120V AC or 220-240V AC) or some other voltage (like for example car 12-14VDC or 24V DC used in industrial automation and trucks). Depending on the application the power supply can provide isolation (almost always needed in mains power supplies for safety and preferred on industrial electronics) or can be non-isolated (many 12V DC powered electronics).

AC/DC power supplies can be classified into one of two primary families: internal or external. Internal power supplies are those which will be installed within some end device as a component; external power supplies accompany an end device as a stand-alone sub-assembly. Internal and external power supplies vary greatly in the degree of engineering effort required to successfully implement the power source as an element of the final system.

Designers know that there is more to a power supply than its ability to provide a steady DC (or AC) voltage despite load and line changes, system transients, noise, and other aberrations.

Here are some article links related to power supplies worth to check out:

Do You Have the Right Power-Supply Protections? article tells that power supply must be able to protect itself against temporary and permanent faults (internal or external), that could cause damage to its load.

Over-current protection in power supplies & converters article tells that AC-DC power supplies and DC-DC converters have internal current-limiting circuits to protect the power device, and to some degree its load. The majority of over-current-protections include an automatic recover feature. There are a number of ways to implement over-current-protection (OCP).

Goodbye 3AG fuse, we’ll miss you article tells that fuses are an essential part of many system designs, and we’ve come to depend on them since the earliest days of electricity. They are simple, reliable, clear cut, and unambiguous components that are used to implement system and user protection as mandated by regulatory standards. Among the most widely-used fuse body sizes is the 3AG size, measuring 6.3×32 mm, which is available in standard ratings from 100 mA to 15 A, in fast-acting, slow-blow, precision, and time-delay versions. This type of fuse fits into a fuseholder socket. The classic fusible link design represented but not limited to the 3AG style is not physically compatible with many of today’s compact product units. To meet the size needs and non-replaceable preferences while retaining the virtues of a “hard” fuse and circuit break, vendors are now offering surface-mount fuses.

Mean Well article Leakage Current discusses on leakage current in EMC filters. Leakage current in power supplies may occur due to the EMC filters, which utilizes Y capacitors between the live and neutral conductors. This causes some leakage current to flow from the neutral or the live conductor to the power supply casing which is normally connected to the earth ground. Most power supply manufacturers specify this current which should always be lower than 3.5 mA as per the IEC-60950-1 regulations. There are standards that specify maximum leakage currents that are safe for humans under different conditions. These vary with the application and type of possible contact as well as the type of ground connection.

Medical safety standards in power supplies article tells that medical power supplies can be dangerous to patients and users if not properly designed and rated by a valid safety organization.

Installing internal power supplies article tells that internal and external power supplies vary greatly in the degree of engineering effort required to successfully implement the power source as an element of the final system. When designing an internal AC/DC power supply into a system, several factors must be considered surrounding the safety, thermal, and electromagnetic compatibility (EMC) implications of the installation. This article outlines the caveats associated with utilizing an internal power conversion solution in opposition to an external one and provides guidance on achieving a proper installation.

An inrush current limiter is a component used to limit inrush current to avoid gradual damage to components and avoid blowing fuses or tripping circuit breakers. A typical application of inrush current limiters is in the input stage of non-power factor corrected switching supplies, to reduce the initial surge of current from the line input to the reservoir capacitor when the power supply is turned on. Negative temperature coefficient (NTC) thermistors and fixed resistors are often used to limit inrush current.

https://www.edn.com/inrush-limiter-also-provides-short-circuit-protection/ design idea mentions that for containing large amounts of bulk capacitance, controlling inrush currents poses problems. The simplest approach involves placing an inrush-limiting resistor in series with the capacitor bank, but a resistor wastes power and adds a voltage drop. THere are also better alternatives like this for low voltage DC applications like this Inrush limiter also provides short-circuit protection circuit.

Most modern desktop personal computer power supplies conform to the ATX specification, which includes form factor and voltage tolerances. You can read more about them at https://en.wikipedia.org/wiki/Power_supply_unit_(computer)


  1. Tomi Engdahl says:

    UKCA marking and the impact on XP Power products
    On 31st December 2020 the UK will leave the EU Customs Union and the European Single Market.

    The Impact of EN 60335 on Electrical Appliance Safety

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  3. Tomi Engdahl says:

    EEVblog 1377 – The Amazing UNPREDICTABILITY of Fuses!

    How long does it take for your 400mA multimeter fuse to blow at 600mA?
    Grab a chair and watch!
    The amazing unpredictability of fusing current ratings at low overloads.

  4. Tomi Engdahl says:

    Engineer It – How to test power supplies – Measuring Noise

    TI’s Bob Hanrahan demonstrates how to measure noise when testing power supplies.

    For more videos on testing power supplies, check out:
    Overview: http://www.ti.com/testingpoweroverview
    Measuring efficiency: http://www.ti.com/measuringefficiency
    Measuring stability: http://www.ti.com/measuringstability

  5. Tomi Engdahl says:

    Measuring Mains Voltage with Oscilloscopes

    Problems with measuring mains voltages with an oscilloscope, the correct and safe way to do it, and other dangerous methods that must never be used.

  6. Tomi Engdahl says:

    EEVblog #594​ – How To Measure Power Supply Ripple & Noise

    Dave explains what the ripple and noise specifications on a power supply is and how to measure it using different methods on both analog and digital oscilloscopes. From bad techniques through to good, showing the effect of each one. Traps for young players aplenty in this one.
    How do you detect common mode noise issues and ensure that the signal you are measuring is really coming from your device under test?
    Single ended & differential measurement, DIY coax solutions, termination, analog vs digital oscilloscopes, bandwidth limiting, and even oscilloscope probe coax construction issues. It’s all here.

  7. Tomi Engdahl says:

    Power supply design advances like FFRZVS #circuits enable smaller #USB PD #power adapters for portable devices Infineon Technologies AG #ReferenceDesign


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