AC DC Power Supply
Power supplies are electrical circuits and devices that are designed to convert mains power or electricity from any electric source to specific values of voltage and current for the target device...
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This article contains everything you need to know about programmable power supplies and their use.
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A programmable power supply is a method for controlling output voltage using an analog or digitally controlled signal using a keypad or rotary switch from the front panel of the power supply. They control voltage output, current, and, with an AC power supply, the frequency. The components of a programmable power supply include a processor, voltage and current programming circuitry, a current shunt, and read back circuit.
Other features of a programmable power supply include overvoltage, overcurrent, and short circuit protection and temperature compensation. The types of programmable power supplies include modular, benchtop, floor mounted, and rack mounted models. They use standard commands for programmable instruments (SCPI) as their programming language with certain models using proprietary manufacturer programming languages.
The use of a programmable power supply makes it possible to supply power in the form, voltage, current, and frequency that is required as well as introduce, detect, measure, and record errors. While traditional methods of providing power can be useful, such methods are incapable of providing necessary requirements especially for equipment under development (EUD).
Programmable power supplies provide stable and adjustable voltage and frequency conversion in a clean output and offer protection from errors from the grid. They accurately measure input and output from the grid and a device. Integrated circuits (ICs) operate on constant voltage (CV) where there is no control over the current. The load draws current according to what it needs and is beyond any control.
With a programmable power supply, it is possible to control the parameters of the voltage supply using a numeric keypad, rotary encoder, or a PC. The built-in display of a programmable power supply shows the current voltage, current amp, set voltage, set amp, and mode of operation. It provides all the necessary information to monitor and control the input and output.
ATEs are ideal for data collection and use as a diagnostic tool for testing electronics for defense, aerospace, automobiles, and industrial automation. They ensure that end users will have equipment that performs properly and functions as intended without exposing users to dangerous or unsafe electrical current.
The process of an ATE involves the use of computerized equipment to evaluate the functionality, performance, and quality of an electronic device as well as determine the amount of stress a device can endure without failing. It is an automated testing device that requires little human interference to complete the testing process. The electronic devices assessed by an ATE are described as device under test (DUT), unit under test (UUT), and equipment under test (EUT).
A key to the success of an ATE is the use of a programmable power supply that makes it possible to control and monitor the current, voltage, and frequency being supplied or received from the DUT. Several other components are included in the ATE process such as software, test instruments, signal sources, and various probes.
The production of semiconductor integrated circuits relies on the manufacture of a single cell pure silicon crystal. Programmable power supplies are used to control certain processes and monitor crystal growth. A PPS monitors the light source, polyelectrolyte solutions, stirring motors, and heaters and coolers. They provide the power and feedback necessary to control the environment for crystal growth.
X-ray generators are used to examine the composition of materials, metal fatigue testing, medical examinations, and as a diagnostic tool. Programmable power supplies control the electrical power that energizes the x-ray tubes and provide real time control and monitoring of power limits to ensure accuracy. The main components of an x-ray generator are a programmable power supply with emission control circuitry to produce x-rays.
The output for an x-ray generator ranges between 160kV up to 450kV with negative, positive, or bipolar polarity. Proper control of the x-ray tubes by a programmable power supply is essential for producing data and ensuring the long life of the x-ray tubes.
Scanning electron microscopes produce an image using a focused beam of electrons to create an extremely high-resolution image. A programmable power supply affords the ability to program the voltage for the process using an external signal. The results of the process are precise and highly accurate and produce high-resolution images. Modern SEMs have easy to use graphic interfaces, a smaller footprint, and exceptionally powerful programmable power supplies that provide higher resolution, exceptional reliability, and user-friendly communications.
Programmable power supplies play a critical role in the testing and examination of new electronic devices. They provide data that guides engineers as they work to perfect and develop new products. The key factor in the process is the control of current, voltage, and frequency that is provided by programmable power supplies.
Programmable power supplies are used in laboratories to test electronics, prototyping of circuits, and for scientific experimentation. They are ideal for hands-on learning in educational settings.
Programmable power supplies are essential to the controlled testing of electronic devices, environmental testing, and the calibration of various instruments. They ensure the quality, safety, and viability of a product.
The development of any new product is highly dependent on the results procured from research and development, an aspect of new product processing that gives an indication as to the success of a product. During the R and D process, new technologies and exciting new ideas are put through controlled documented tests that rely on control of the power supply to ensure accurate data.
An essential part of modern manufacturing is quality control, which takes the forms of computers, comparators, and other electronic methods. Programmable power supplies are integrated into product manufacturing as part of quality control, automated testing, final testing, and debugging of processes. They ensure that products meet performance parameters before being released to the public.
The classifications of programmable power supplies are first divided by the type of current they monitor and control. DC programmable power supplies are designed to provide stable voltage while AC programmable power supplies provide stabilized voltage and AC waveforms. Additionally, certain forms of AC programmable power supplies act as frequency stabilizers.
DC programmable power supplies provide output voltage in the thousands to tens of thousands range of volts. They come in benchtop, rack mount, module, and PCB mount models with some models capable of AC/DC input. Programmable DC power supplies are further classified as constant voltage and constant current according to whether the output is stabilized voltage or current, which changes as the load changes based on Ohm’s law.
A DC power supply supplies constant current or voltage and are classified as linear regulators or switching regulators according to the method of control. The types of DC programmable power supplies include benchtop models and rack mount models. They provide regulated DC power output to components, modules, and devices and deliver voltage and current that is stable and precise with minimal noise. The two main and essential settings on a DC programmable power supply are output voltage and current limit. These settings are combined with the load, which determines how the power supply will operate.
The two modes of a DC programmable power supply are:
The output voltage is determined by the settings of the user while the output current is determined by the resistance of the load.
The CC mode is the safety mode but can have other purposes. The current is constant and is coordinated by the user’s current limit setting. If the power supply is in CV mode but exceeds the current limit, it will switch to the CC mode but can revert back if the load current falls below the current limit setting.
The essential elements of a DC programmable power supply are the maximum voltage, maximum current, and maximum power, each of which ensures that the required voltage and current levels are delivered.
An AC programmable power supply supplies alternating current to help test pieces of equipment by simulating grid interruptions, harmonics, and surges that could damage a DUT. They are used in electrical testing in aerospace, lighting, labs, and production of military equipment. An AC programmable power supply makes it possible to generate alternating current from 45 Hz up to 500 Hz, which can be produced in different forms such as surges, traps, and dimmed phase waves. Various forms are designed to simulate different events.
AC current has a sine wave shape where the amplitude is voltage and the frequency is measured in seconds. The shape of sine waves vary in their measurement between nations of the world.
Benchtop programmable power supplies are light enough to be placed on a supported flat surface such as a workbench. They are standalone units for circuit testing and development. Benchtop programmable power supplies, as with all programmable power supplies, have low output noise and layers of protection to prevent damage to DUTs.
Electrical engineers and circuit designers use benchtop programmable power supplies for testing and measuring various pieces of electrical equipment, such as circuit boards or other electronic products. Benchtop programmable supplies can be single channel or multiple channels with single channel having one output that can be controlled while multiple channels can have three or four channels to be controlled.
In addition to the differences of channels, there is a difference in polarity. Power supplies can be bi-polar or unipolar where bi-polar supplies can function in the negative voltage realm and positive voltage realm while unipolar power supplies can only provide positive voltage. Unipolar power supplies can be adjusted for negative voltage by switching the leads.
The two most common types of benchtop programmable power supplies are linear programmable power supplies versus switching programmable power supplies. Linear programmable power supplies are heavier, larger, and deliver less power with less efficiency but tend to have greater accuracy with little noise. Switching programmable power supplies are smaller, lighter, and deliver a tremendous amount of power but generate high frequency noise.
A special feature of benchtop programmable power supplies is their ability to simulate a battery. Such benchtop programmable power supplies have an option to add an internal resistance that will operate as though there is a resistor in a series of positive output terminals, a structure that simulates the operation of a battery.
As with most programmable power supplies, benchtop programmable power supplies have the ability to set a constant current or constant voltage.
Rack mounted programmable power supplies are placed in a support rack with several programmable power supplies stacked in a single rack. They can be used as stand-alone power supplies or be connected to supply larger voltages or current to multiple devices. Rack mounted programmable power supplies can operate in constant voltage mode, constant current mode, and constant power mode, as with all forms of programmable power supplies.
Control of voltage and current in a rack mounted programmable power supply can be slew rate, arbitrary waveform generation, and internal resistance simulation like a benchtop programmable power supply with display brightness control, which is necessary for rack mounted programmable power supplies. An important feature of rack mounted programmable supplies is remote control using LAN, USB, and built in analogue interfaces.
Standard models of rack mounted programmable power supplies have an output range of 200 W up to 15 kW with paralleling making it possible to achieve 60 kW with outputs of up to 1500 V.
Chassis mounted programmable power supplies are placed into a chassis or frame. They include linear power and switching power supply models with each type being able to convert AC current into DC current depending on the needs of an application. Chassis mounted programmable power supplies are mounted into a chassis, which can take various forms. The controls for a chassis mounted programmable power supply are placed on the front plate of the chassis.
The various forms of chassis mounted programmable power supplies include chassis models that are enclosed, U chassis, and L chassis. U chassis models have an open frame and can come with or without a cover. They are designed for thermal conductivity, EMC protection, and have flexible mounting options.
Enclosed power supplies have their components fixed to a base PCB and have a case that covers the internal components. The enclosures for enclosed programmable power supplies can be made of metal or other types of materials. The purpose for enclosing the power supply is to provide safety and to protect the internal components from interference. Although open frame programmable power supplies have some positive features, they lack the protection and safety offered by an enclosed power supply.
Digital programmable power supplies provide precision control and monitoring through a digital interface and encoder knob. Specifications are digitally entered and digitized to be fed back to the converter. Once the parameters are entered, the programmable power supply calculates the compensation factor to determine the pulse width modulation (PWM) duty cycle and the output waveform.
Analog programmable power supplies use knobs and dials to adjust the parameters of the output. They are less precise than digital programmable power supplies, are preferred for their simplicity, and are applicable for certain applications. The analog control circuit provides feedback to the primary control circuit using conventional voltage and current sensing systems, error amplifiers, and optocouplers, which is a semiconductor that permits the passage of an electrical signal between two circuits.
When a programmable power supply needs to operate at a specific input, output, wattage, and form, an analog programmable power supply is an ideal solution. Analog controls are very stable, perform without any problems, and have fewer difficulties or glitches.
The problem with analog programmable power supplies is their inflexibility. Any changes to the settings require adjustments to the design of the power supply. As reliable as they are, analog programmable power supplies are best suited for applications where there won’t be any need for adjustments during processing. They make it possible to monitor the status but do not have advanced monitoring and control abilities.
All programmable power supplies take electric power from a source at its input and transform it to deliver it to the load. The input and output can be AC or DC current with DC current preferred for electronic devices since it flows in a constant direction. AC current is used to deliver power through power transmission lines and periodically inverts its direction.
The various types of programmable power supplies have to be configured and designed to meet the needs of a variety of electronic devices and applications. They are programmed with the parameters required.
With programmable power supplies, the output voltage is continually sampled and adjusted to help maintain the required value. Included are additional control methods for current and voltage limits, noise filtering, and output adjustments. The main types of programmable power supplies are linear and switched based with linear based models being the least complex and simplest.
The main use for linear programmable power supplies is in applications where precision control is necessary and removal of noise is important. They are the least efficient of the types of programmable power supplies but offer the best performance. The name of linear programmable power supplies comes from the power supplies not using switches as a means to regulate the voltage output.
Basic linear power supplies have been available for many years and were the first type of power supply. Through the introduction of various controls and technological advancements, linear programmable power supplies have been modernized for use in the 21st century.
The components of linear programmable power supplies are larger and heavier than those of switched programmable power supplies, which makes them more cumbersome and increases the amount of heat they generate. Although they have increased accuracy, linear programmable power supplies are 50% less efficient than switched programmable power supplies.
Linear programmable power supplies are used in applications that require exceptional regulation, low ripple, low electromagnetic emissions, and an excellent transient response. They step down their input voltage to allow for a lower output voltage. The adjustment of the voltage is provided by a transformer that drops the voltage from an AC source to a lower AC voltage using a series of rectifier circuits and filters to provide DC voltage.
Switched programmable power supplies are complex and complicated devices that have versatility in polarity and are far more efficient than linear programmable power supplies. Regardless of their complexity, switched programmable power supplies are smaller, lighter, and less expensive than linear programmable power supplies.
A critical feature of switched programmable power supplies is the small loss across the switch due to the fact that they operate at a higher frequency. As productive as this feature may be, the process radiates noise that can interfere with other circuits. These disadvantages are compensated for by a switched programmable power supply’s wide input voltage range matched with a higher output range, which increases their efficiency.
The downsides of switched programmable power supplies are their complex circuitry, pollution of AC mains, noise level, and their high operating frequency, which has to be suppressed with shielding or other forms of protection.
The wide use of switched programmable power supplies is due to the reduction in the size of electronic devices and the demand for more portability. A switched programmable power supply uses semiconductors to regulate and convert energy by switching off and on at a rapid rate.
The types of switched programmable power supplies include:
Traditional power supplies are fixed and have few options or adjustments while programmable power supplies are flexible and have multiple modes. Programmable power supplies allow users to control different settings including variable voltage, current, power, and mode of operation that are adjusted according to the users needs.
The benefits of controlling these factors include:
A battery charger, with a programmable power supply, can supply constant current at the beginning of the charging cycle but switch to constant voltage (CV) as the battery nears full charge. If the power supply exceeds the current limit in the CV mode, it automatically switches back to constant current mode. In the constant current (CC) mode, a programmable power supply regulates the current, which is defined as the safe mode. The output current is controlled by the settings of the user, which also applies to the constant voltage.
The components of a programmable power supply include a transformer, rectifier, filter, and regulator circuits. They provide uninterrupted power supply to several devices and are used in experimentations when control of current and voltage are a necessity.
A transformer in a programmable power supply is a static component used to transfer electrical energy from the primary winding to the secondary winding without affecting the frequency and is used to step up or step down the AC voltage level. Additionally, the transformer isolates the voltage of the electronic system from the AC power.
In a transformer, the primary winding is connected to an AC voltage source, while the secondary winding is connected to the load. Although energy is transferred from the primary winding to the secondary winding, the two windings are not connected. Energy is passed between them due to electromagnetic induction where there is induced voltage in the secondary winding.
In a programmable power supply, the main functions of the transformer are stepping the voltage up, stepping the voltage down, and providing isolation between the primary and secondary circuits.
The rectifier or diode in a programmable power supply changes AC power into pulsating DC power. The diode is a unidirectional component that operates as a rectifier in the forward direction. The circuits of a rectifier using a diode are half wave, full wave center tapped, and full wave bridge type.
Half wave rectification is not used for the majority of power applications. It is a simple method for reducing power to resistive loads.
Full wave rectification center tapped is used to rectify AC power to get full use of the half cycles of the sine wave. A full wave rectifier with a center tap design is used with a transformer that has a center tapped secondary winding and two diodes.
A full wave bridge rectifier has a four-diode bridge design and converts the complete AC signal into DC signal. It is the most used type of rectifier. Full wave bridge rectifiers convert positive and negative half cycles of AC current into DC current and provide double output voltage compared to half wave rectifiers, which is possible due to the four diodes.
In a programmable power supply, the filter is designed to keep the ripple component from appearing in the output. It converts pulsating DC current from the rectifier circuit into a smooth DC level. The types of filters are capacitance (C filter) and resistor capacitor (RC filter).
C filters are the simplest form of filter and the most economical. RC filters are used to reduce ripple voltage on C filters and pass the DC component. They filter by blocking some frequencies while allowing others to pass. The two types of RC filters are high pass filters and low pass filters. High pass filters allow signals to pass above its cut off point while low pass filters allow signals to pass that are below its cut off point.
The purpose of filters is to control the ripple factor, which is the unwanted AC component of the signal that occurs after rectification and is unwanted because it can damage the load. Filters smooth the signal and suppress the AC component. The ripple factor is the ratio of the root mean square of the ripple voltage to the value of DC components at the output voltage and may be expressed as a percentage. The calculation of the ripple factor determines the effectiveness of the filter.
The main purpose of a programmable power supply is to supply a steady output voltage such that the load operates correctly. The output level has to be maintained regardless of any variation in the input voltage. A transistor voltage regulator is a series voltage regulator and shunt voltage regulator.
The series voltage regulator controls unregulated input voltage that goes to the output and uses a circuit to sample the output to get feedback for the comparator circuit, which compares the sample to the reference voltage. The shunt voltage regulator shunts current away from the load in order to regulate the output voltage.
An integrated circuit (IC) unit contains the reference source, comparator, amplifier, control device, and overload protector. Each of these factors are controlled in a programmable power supply by the user who sets the IC regulators output values.
The ITECH IT7321 uses linear amplification and has the ability to produce signals that are accurate copies of the input. It is widely used in avionics due to its ability to comply with the rigorous testing requirements for examining electronic equipment for aviation and being able to operate at 400 Hz AC during testing. The ITECH IT7321 makes it possible to perform tests easily, accurately, and with high resolution.
The PLS series single output programmable DC power supply has voltage ratings offering DC output voltages of 30V, 50V, 100V, 200V, and 400V with a 600 W to 1500 W power rating. The wide range makes it possible to have a variety of voltage and current ratings from a single unit. The PLS series can operate in a series, parallel or both, which allows for voltages up to 800V and power up to 6 kW. Remote control of the PLS series can be via USB, ethernet, and analog control inputs.
The EDU36311A is a triple output power supply that easily fits on a workbench. All outputs can be monitored simultaneously on the unit's 7-inch color display. Each of the outputs is independent making it possible to connect outputs in a series for higher voltages, parallel for additional current, or stacked. The sequencing feature on the EDU36311A makes it possible to enable or disable outputs in a set pattern. The control logic of the unit can be activated before applying power to a device. The EDU36311A has proprietary software for remote control and data logging.
The Sequoia series is a four-quadrant regenerative grid simulator with an optional regenerative electronic load mode. The series provides flexibility with high power to create an advanced platform for AC solutions. The Sequoia series uses SIC power switching with a compact robust design mounted on a floor standing chassis. It is an easy to configure power source with single and multiphase AC or single channel and multichannel DC power. The Sequoia series can power equipment for power conditioning, grid interactive green energy, and power distribution generation.
The GENESYS+™ is a lightweight, portable user-friendly programmable power supply with a multifunctional front panel, isolated analog, and optional communication interfaces. It has power levels of 30kW, 45kW and 60kW with a 23U rack system profile. A distinctive feature of the GENESYS+™ is its low noise output that is combined with output voltages of 10V up to 600V and AC input options that include built in active power factor correction offered in a three phase 208 VAC input or three phase 400 VAC or 480 VAC. The GENESYS+™ features programmable slew rate control, constant power limit control, an arbitrary waveform generator with auto trigger, and internal resistance programming.
There are an endless number of uses for programmable power supplies. In many incidences, they are an essential part of a test, diagnosis, or protection of an electrical device. The selection process for a programmable power supply involves the examination of specific key factors that will ensure its successful use.
The selection of a programmable power supply begins with determining the voltage and current that is required by an application. The output levels must be able to meet the requirements of the testing or necessary power needs. The programmable power supply should be able to deliver maximum and minimum values without loss of precision or safety. Selecting a programmable power supply with exceptionally high voltage or current can have a negative effect on the accuracy of the power it delivers.
The features of programmable power supplies are one of the reasons for their popularity since each type of programmable power supply has the potential of having a wide range of controls and data feedback. The essential features of any programmable power supply are the ability to control voltage and current limits. Although most programmable power supplies have a remote-control option, the type of remote control needs to be considered. Other common features are ramping, sequencing, over current and over voltage protection, electronic current limiting, and thermal resets.
Output stability refers to a programmable power supply's ability to maintain consistent voltage and current levels under varying load conditions over time. The information regarding this aspect of a programmable power supply is included in its specifications, which include load and line regulations that indicate how well it can maintain stability. A programmable power supply with excellent stability is a necessity for applications that need precision and a stable power output. The final decision regarding programmable power supply selection is matching it with the needs of the application.
Having more than one output improves efficiency and makes it possible to connect multiple loads to one programmable power supply. When purchasing a programmable power supply with multiple outputs, it is important that each output be isolated and operate separately or in parallel to provide more flexibility.
This particular feature is optional but is normally recommended since it allows the user to turn an output on or off without having to shut off the load supply. It makes it possible to set different tests without being concerned about how they will affect the load.
Constant voltage is standard on all programmable power supplies since they are made to draw current for testing with no impact to voltage stability. There are times when it is necessary to switch to constant voltage mode such as delivering sequence stepped voltage.
The quick and easy setup of a programmable power supply makes it possible to spend more time on testing and monitoring of an application. Programmable power supplies can come with intuitive features that make it possible to have an efficient and rapid setup. Units with separate voltage and current controls and fine-tuning controls provide greater precision.
An important aspect of the success of a programmable power supply is temperature control, which keeps them safe and reliable. It is very advisable to purchase a programmable power supply with a high-powered cooling unit built in the system. There are several forms of cooling designs to choose with each type designed for a specific form of programmable power supply.
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