Regulated power supply

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A regulated power supply is an embedded circuit; it converts unregulated AC (alternating current) into a constant DC. With the help of a rectifier it converts AC supply into DC. Its function is to supply a stable voltage (or less often current), to a circuit or device that must be operated within certain power supply limits. The output from the regulated power supply may be alternating or unidirectional, but is nearly always DC (direct current). [1] The type of stabilization used may be restricted to ensuring that the output remains within certain limits under various load conditions, or it may also include compensation for variations in its own supply source. The latter is much more common today.

Contents

Applications

D.C. variable bench supply

D.C. variable bench power supply unit, with a digital display showing current (left) and voltage (right), and three banana connectors (+, ground, -). Other power supplies may use the opposite order for indicators and connectors, and two different colours for the indicators. Bench power supply.jpg
D.C. variable bench power supply unit, with a digital display showing current (left) and voltage (right), and three banana connectors (+, ground, -). Other power supplies may use the opposite order for indicators and connectors, and two different colours for the indicators.

A bench power supply usually refers to a power supply capable of supplying a variety of output voltages useful for BE (bench testing) electronic circuits, possibly with continuous variation of the output voltage, or just some preset voltages. Some have multiple selectable ranges of current/voltage limits which tend to be anti-proportional. [2] [3] [4]

A laboratory ("lab") power supply normally implies an accurate bench power supply, while a balanced or tracking power supply refers to twin supplies for use when a circuit requires both positive and negative supply rails).

Types

Variable bench power supplies exist both as linear (transformer first) and switched-mode power supply (full-bridge rectifier first), each with a different set of benefits and disadvantages:

Linear

The linear type produces only very little noise (or "ripple voltage") and is less prone to external electromagnetic and radio frequency interference (EMI, RFI), making it preferable for audio equipment and radio-related applications and for powering delicate circuitry. [5] Linear power supplies also have fewer failable parts which increases longevity, [lower-alpha 1] and have a quicker transient response. Linear variable bench power supplies have existed since longer ago, dating back at least to the 1980s. [6] [7] [8] Linear power supplies typically make clicking sounds while adjusting the voltage, caused by adjustment between transformer taps. This is done to reduce energy wasted to heat by widening or narrowing the selected section of the secondary side of the transformer to be as close above the user-selected output voltage as possible. [9] [10]

Switching

Switching-mode power supplies are more lightweight, efficient, and more compact at a similar power rating, making them suitable for high-power applications. The higher efficiency means less heat production at the same output power, thus less wasted energy and needed cooling. Additionally, they may be able to operate on a wider Mains input voltage range, typically around 110 to 240 volts rather than a section of approximately twenty volts on only end of the range, to be able to operate internationally. Similar switching technology is used in AC adapters that charge battery-powered devices including mobile phones, laptop computers, and electric bicycles. [11]

Other

Some high-current power supplies have a rear-sided output for high-current operation. Its poles are larger to support such currents and are usually initially covered by plastic caps. The poles can be connected to accordingly-sized crocodile clamps. [12] [2]

Functionality and controls

The front panel typically has LED indicators for "C.V." ("constant voltage") and "C.C." ("constant current"). When the current demanded by the load exceeds the limit set by the user, the power supply automatically switches to the latter mode by regulating the voltage down so much as to prevent the current limit from being exceeded.

Controls vary between power supply models. Many have rotary knobs for setting voltage and current, each usually with a "coarse" and "fine" knob, the former of which adjusts the parameter throughout the entire range, whereas the latter facilitates adjustment within a small surrounding range. Some models lack the "fine" knob for current, as drawn electrical current is decided by the load at a given voltage, thus less important to be throttled precisely. [13]

Some, typically higher-end models, are equipped with additional features such as a button for toggling output power without having to switch the whole device on/off, a memory for shortcuts to voltage/current combinations, an option to automatically cut out power when reaching a current limit specified by the user ("over-current protection"), likewise over-voltage protection that cuts out power if the external voltage exceeds output, indicator displays with more digits (four or five instead of three), digital rather than analogue voltage control, and the ability to lock the power setting to prevent accidental adjustment. [14] In addition to output voltage/current meters, few are equipped with a wattage (power) meter which indicates the product of both in real time, and a USB charging port. [15] [16] [17]

Many models have a handle at the top for carrying. For cooling, a heat sink, fan, or both may be used. Heat sinks may be mounted externally or internally. Heat sinks are silent, whereas fans are more effective in cooling. Fan speed may adjust based on temperature or output current, the former of which cools faster while idle or low throughout intermittent power output, whereas the latter provides acoustic feedback of how much current is output. [13] [17]

Some power supplies have two output channels. These may be used at schools, as a multi-channel unit tends to cost less than two separate units due to shared hardware. High-end ones might allow internally connecting two channels to a series circuit to double the voltage limit. Few power supplies have a third auxiliary output channel that is typically less powerful. It is typically located near the right edge or at the center. [18] [19]

Bench power supply units equipped with an integrated voltmeter panel to measure external voltages have existed in the 1990s and possibly earlier, but portable multimeters have made that feature obsolete. [6]

Other applications

Fixed-voltage power supplies like these and AC adapters are optimized with the aim to support high currents per physical space at a given constant voltage. Due to optimization for a specific voltage rather than a range, they tend to be more compact at a similar output power support. Netzgeraet-orig.jpg
Fixed-voltage power supplies like these and AC adapters are optimized with the aim to support high currents per physical space at a given constant voltage. Due to optimization for a specific voltage rather than a range, they tend to be more compact at a similar output power support.

Topology and technology

Many topologies have been used since the regulated supply was invented. Early technologies included iron-hydrogen resistors, resonant transformers, nonlinear resistors, loading resistors, neon stabiliser tubes, vibrating contact regulators etc.

Modern regulated supplies mostly use a transformer, silicon diode bridge rectifier, reservoir capacitor and voltage regulator IC. There are variations on this theme, such as supplies with multiple voltage lines, variable regulators, power control lines, discrete circuits and so on. Switched mode regulator supplies also include an inductor.

At times regulated supplies can be much more complex. An example supply from a 1980s TV which used bidirectional interaction between the main supply and the line output stage to operate, generating a range of output voltages with varying amounts of stabilisation. Since neither stage could start without the other running, the supply also included a kickstart system to pulse the system into operation. The supply also monitored voltages in the TV power circuitry, shutting down if these voltages went out of spec. For special applications, supplies can become even more complex.

Related Research Articles

In electrical engineering, the power factor of an AC power system is defined as the ratio of the real power absorbed by the load to the apparent power flowing in the circuit. Real power is the average of the instantaneous product of voltage and current and represents the capacity of the electricity for performing work. Apparent power is the product of root mean square (RMS) current and voltage. Due to energy stored in the load and returned to the source, or due to a non-linear load that distorts the wave shape of the current drawn from the source, the apparent power may be greater than the real power, so more current flows in the circuit than would be required to transfer real power alone. A power factor magnitude of less than one indicates the voltage and current are not in phase, reducing the average product of the two. A negative power factor occurs when the device generates real power, which then flows back towards the source.

<span class="mw-page-title-main">Rectifier</span> Electrical device that converts AC to DC

A rectifier is an electrical device that converts alternating current (AC), which periodically reverses direction, to direct current (DC), which flows in only one direction. The reverse operation is performed by an inverter.

<span class="mw-page-title-main">Power supply</span> Electronic device that converts or regulates electric energy and supplies it to a load

A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power.

<span class="mw-page-title-main">Power inverter</span> Device that changes direct current (DC) to alternating current (AC)

A power inverter, inverter, or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the opposite of rectifiers which were originally large electromechanical devices converting AC to DC.

In electronics, a linear regulator is a voltage regulator used to maintain a steady voltage. The resistance of the regulator varies in accordance with both the input voltage and the load, resulting in a constant voltage output. The regulating circuit varies its resistance, continuously adjusting a voltage divider network to maintain a constant output voltage and continually dissipating the difference between the input and regulated voltages as waste heat. By contrast, a switching regulator uses an active device that switches on and off to maintain an average value of output. Because the regulated voltage of a linear regulator must always be lower than input voltage, efficiency is limited and the input voltage must be high enough to always allow the active device to reduce the voltage by some amount.

<span class="mw-page-title-main">Switched-mode power supply</span> Power supply with switching regulator

A switched-mode power supply (SMPS), also called switching-mode power supply, switch-mode power supply, switched power supply, or simply switcher, is an electronic power supply that incorporates a switching regulator to convert electrical power efficiently.

A DC-to-DC converter is an electronic circuit or electromechanical device that converts a source of direct current (DC) from one voltage level to another. It is a type of electric power converter. Power levels range from very low to very high.

<span class="mw-page-title-main">Voltage regulator</span> System designed to maintain a constant voltage

A voltage regulator is a system designed to automatically maintain a constant voltage. It may use a simple feed-forward design or may include negative feedback. It may use an electromechanical mechanism, or electronic components. Depending on the design, it may be used to regulate one or more AC or DC voltages.

<span class="mw-page-title-main">AC adapter</span> Type of external power supply

An AC adapter or AC/DC adapter is a type of external power supply, often enclosed in a case similar to an AC plug. AC adapters deliver electric power to devices that lack internal components to draw voltage and power from mains power themselves. The internal circuitry of an external power supply is often very similar to the design that would be used for a built-in or internal supply.

<span class="mw-page-title-main">Flyback transformer</span> High frequency pulse transformer, commonly used to drive cathode ray tubes

A flyback transformer (FBT), also called a line output transformer (LOPT), is a special type of electrical transformer. It was initially designed to generate high-voltage sawtooth signals at a relatively high frequency. In modern applications, it is used extensively in switched-mode power supplies for both low (3 V) and high voltage supplies.

<span class="mw-page-title-main">Welding power supply</span>

A welding power supply is a device that provides or modulates an electric current to perform arc welding. There are multiple arc welding processes ranging from Shielded Metal Arc Welding (SMAW) to inert shielding gas like Gas metal arc welding (GMAW) or Gas tungsten arc welding (GTAW). Welding power supplies primarily serve as devices that allow a welder to exercise control over whether current is alternating current (AC) or direct current (DC), as well as the amount of current and voltage.

<span class="mw-page-title-main">Inrush current</span> Maximal instantaneous input current drawn by an electrical device when first turned on

Inrush current, input surge current, or switch-on surge is the maximal instantaneous input current drawn by an electrical device when first turned on. Alternating-current electric motors and transformers may draw several times their normal full-load current when first energized, for a few cycles of the input waveform. Power converters also often have inrush currents much higher than their steady-state currents, due to the charging current of the input capacitance. The selection of over-current-protection devices such as fuses and circuit breakers is made more complicated when high inrush currents must be tolerated. The over-current protection must react quickly to overload or short-circuit faults but must not interrupt the circuit when the inrush current flows.

<span class="mw-page-title-main">Low-dropout regulator</span> DC linear voltage regulator

A low-dropout regulator is a type of a DC linear voltage regulator circuit that can operate even when the supply voltage is very close to the output voltage. The advantages of an LDO regulator over other DC-to-DC voltage regulators include: the absence of switching noise ; smaller device size ; and greater design simplicity. The disadvantage is that linear DC regulators must dissipate heat in order to operate.

In electronics, a bleeder resistor, bleeder load, leakage resistor, capacitor discharge resistor or safety discharge resistor is a resistor connected in parallel with the output of a high-voltage power supply circuit for the purpose of discharging the electric charge stored in the power supply's filter capacitors when the equipment is turned off, for safety reasons. It eliminates the possibility of a leftover charge causing electric shock if people handle or service the equipment in the off state, believing it is safe. A bleeder resistor is usually a standard resistor rather than a specialized component.

An H-bridge is an electronic circuit that switches the polarity of a voltage applied to a load. These circuits are often used in robotics and other applications to allow DC motors to run forwards or backwards. The name is derived from its common schematic diagram representation, with four switching elements configured as the branches of a letter "H" and the load connected as the cross-bar.

Current limiting is the practice of imposing a limit on the current that may be delivered to a load to protect the circuit generating or transmitting the current from harmful effects due to a short-circuit or overload. The term "current limiting" is also used to define a type of overcurrent protective device. According to the 2020 NEC/NFPA 70, a current-limiting overcurrent protective device is defined as, "A device that, when interrupting currents in its current-limiting range, reduces the current flowing in the faulted circuit to a magnitude substantially less than that obtainable in the same circuit if the device were replaced with a solid conductor having compatible impedance."

<span class="mw-page-title-main">LM317</span> Adjustable linear voltage regulator

The LM317 is an adjustable positive linear voltage regulator. It was designed by Bob Dobkin in 1976 while he worked at National Semiconductor.

<span class="mw-page-title-main">Power supply unit (computer)</span> Internal computer component that provides power to other components

A power supply unit (PSU) converts mains AC to low-voltage regulated DC power for the internal components of a desktop computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the main voltage

<span class="mw-page-title-main">78xx</span>

78xx is a family of self-contained fixed linear voltage regulator integrated circuits. The 78xx family is commonly used in electronic circuits requiring a regulated power supply due to their ease-of-use and low cost.

<span class="mw-page-title-main">Capacitive power supply</span>

A capacitive power supply or capacitive dropper is a type of power supply that uses the capacitive reactance of a capacitor to reduce higher AC mains voltage to a lower DC voltage.

References

  1. ↑ A quality switching-mode power supply can outlive a poorly designed linear one, but as linear power supplies rely on fewer delicate components, they tend to be less prone to failure.
  1. ↑ Regulated Power Supplies at Google Books
  2. 1 2 "Bedienungsanleitung Labornetzgerät PS900W" (PDF) (in German). 2017. Retrieved 2021-08-21.
  3. ↑ https://www.sparkfun.com/datasheets/Tools/382260_UM.pdf [ bare URL PDF ]
  4. ↑ https://maplindownloads.s3-eu-west-1.amazonaws.com/n93cx-3658.pdf [ bare URL PDF ]
  5. ↑ "Linear vs Switching Power Supplies". Advanced Conversion Technology. Retrieved 25 August 2021.
  6. 1 2 "Bausatzanleitung Labornetzgerät UNIWATT NG 304 (0...30V / 0...3A)" (PDF) (in German). 1997.
  7. ↑ Roggenhofer, Peter (1988). "Labor-Netzgerät Uniwatt NG-500 Power-S Beha-Amprobe;". www.radiomuseum.org (in German).
  8. ↑ "Linear Power Supplies for Audiophiles - Getting Closer to Live". Audio Bacon. 29 June 2018. Retrieved 25 August 2021.
  9. ↑ "StackPath". www.ecmweb.com. 1999-11-01. Retrieved 25 August 2021. Using a tap changes the voltage ratio of a transformer so that its secondary voltage stays at nominal.
  10. ↑ "Understanding Linear Power Supply Operation" (PDF). 2005-02-04. Retrieved 25 August 2021.
  11. ↑ "Linear Power Supply vs. Switching Power Supply: Advantages and Disadvantages". resources.pcb.cadence.com. 2020. Retrieved 21 August 2021.
  12. ↑ Geti Laboratory power supply PS3020 0-30V/ 0-20A
  13. 1 2 Voltcraft (2015). "OPERATING INSTRUCTIONS – LABORATORY POWER SUPPLY UNIT (LPS 1305)" (PDF). asset.conrad.com. p. 4. Retrieved 22 August 2021.
  14. ↑ "Korad KA3005D-2S user manual" (PDF). 2012.
  15. ↑ "DC Power Supply PS-3010DF User Manual" (PDF). Long Wei. (via Manual - Dr.meter)
  16. ↑ DPS-305BF with four digits after decimal on current meter, but only two on voltage meter.
  17. 1 2 "Labornetzteil Test: Korad / RND 320 KA3005P - mit Videos". afug-info.de (in German). AFUG INFO. December 2018. Retrieved 26 September 2021.
  18. ↑ Voltcraft VLP 2403 PRO: outputs A and B with 0-40V 3A, Output C with 3-6V 2A
  19. ↑ "Power Supply Design: Switch-Mode vs. Linear". Simply Smarter Circuitry Blog. 23 October 2014. Retrieved 25 August 2021.
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