Programmable Power Supplies (PPS)

Chapter One: What is a Programmable Power Supply?

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.

Programmable power supplies come with various functionalities such as protection against overvoltage, overcurrent, and short circuits, along with temperature regulation. They are available in several forms, including modular, benchtop, floor-standing, and rack-mounted configurations. These devices generally employ Standard Commands for Programmable Instruments (SCPI) for programming, although some models may use proprietary languages specific to the manufacturer.

Chapter Two: What are the uses for programmable power supplies?

Utilizing a programmable power supply enables the delivery of power tailored to specific requirements such as desired voltage, current, and frequency. It also allows for the introduction, detection, measurement, and logging of errors. Unlike conventional power supply methods, which can be useful but often fall short of meeting the precise needs of equipment under development (EUD), programmable power supplies offer enhanced versatility and control.

Programmable power supplies deliver stable and adjustable voltage and frequency with a clean output and safeguard against grid-related errors. They provide precise measurements of both input and output for connected devices. Integrated circuits (ICs) function on a constant voltage (CV) basis where current control is absent, meaning the load dictates the current it requires, which is beyond the system's control.

With a programmable power supply, users can adjust voltage parameters using various interfaces, such as a numeric keypad, rotary encoder, or a computer. The device’s built-in display provides real-time information on voltage, current, settings, and operational mode, allowing for comprehensive monitoring and control of both input and output.

Automatic Test Equipment (ATE)

Automatic Test Equipment (ATE) is highly effective for gathering data and serves as a diagnostic tool in testing electronics across sectors like defense, aerospace, automotive, and industrial automation. It guarantees that end users receive equipment that operates correctly and meets intended specifications while protecting them from hazardous electrical currents.

ATE systems utilize computerized technology to assess the functionality, performance, and quality of electronic devices. They also measure the endurance of a device under various stress conditions before it fails. Designed for minimal human intervention, ATE is an automated testing apparatus that evaluates devices, which are referred to as Device Under Test (DUT), Unit Under Test (UUT), or Equipment Under Test (EUT).

An essential element in the effectiveness of ATE is the incorporation of a programmable power supply, which allows precise control and monitoring of the current, voltage, and frequency provided to or received from the DUT. The ATE setup also typically includes additional components such as specialized software, test instruments, signal generators, and various probes.

Semiconductor Fabrication

In semiconductor integrated circuit production, the creation of a single-cell pure silicon crystal is crucial. Programmable power supplies (PPS) play a vital role in regulating and overseeing various processes involved in crystal growth. They manage the light sources, polyelectrolyte solutions, stirring motors, and temperature control devices such as heaters and coolers. By supplying power and providing essential feedback, PPS helps maintain the optimal conditions for crystal development.

X-Ray Generators

X-ray generators are utilized for analyzing material composition, conducting metal fatigue tests, performing medical diagnostics, and other applications. Programmable power supplies are crucial in regulating the electrical power that energizes x-ray tubes, offering real-time control and monitoring of power limits to ensure precise operation. A key component of an x-ray generator is the programmable power supply, which features emission control circuitry to facilitate x-ray production.

X-ray generators can produce outputs ranging from 160kV to 450kV and support various polarities, including negative, positive, or bipolar. Effective management of the x-ray tubes by a programmable power supply is vital for generating accurate data and extending the lifespan of the x-ray tubes.

Scanning Electron Microscopes (SEM)

Scanning electron microscopes (SEMs) generate high-resolution images by focusing a beam of electrons onto a specimen. A programmable power supply allows for precise voltage control through external signals during the imaging process. This results in highly accurate and detailed images. Contemporary SEMs feature intuitive graphical interfaces, compact designs, and advanced programmable power supplies that enhance resolution, reliability, and ease of communication.

Programmable power supplies are essential for testing and analyzing new electronic devices. They deliver crucial data that supports engineers in refining and advancing product designs. The pivotal aspect of this process is the precise regulation of current, voltage, and frequency provided by these power supplies.

Other Programmable Power Supply Uses

Laboratory

In laboratory environments, programmable power supplies are utilized for testing electronic components, prototyping circuits, and conducting scientific experiments. They are also well-suited for practical learning experiences in educational contexts.

Test and Measurement

Programmable power supplies are crucial for precise testing of electronic devices, environmental assessments, and instrument calibration. They help maintain the quality, safety, and reliability of products throughout these processes.

R and D (Research and Development)

The success of any new product heavily relies on the insights gained from research and development (R&D), which assess the product’s potential. During the R&D phase, emerging technologies and innovative concepts undergo rigorous, controlled tests where precise power supply management is crucial for obtaining accurate data.

Manufacturing

Quality control is a vital component of contemporary manufacturing, utilizing computers, comparators, and various electronic techniques. Programmable power supplies are incorporated into this quality control process, contributing to automated testing, final inspections, and debugging. They help ensure that products adhere to performance standards before they are made available to consumers.

Chapter Three: What are the different types of programmable power supplies?

Programmable power supplies are categorized based on the type of current they manage and control. DC programmable power supplies are designed to deliver stable voltage, while AC programmable power supplies offer both stabilized voltage and AC waveforms. Some AC programmable power supplies also function as frequency stabilizers.

DC programmable power supplies can deliver output voltages ranging from thousands to tens of thousands of volts. They are available in various configurations, including benchtop, rack-mounted, modular, and PCB-mounted models, with some supporting both AC and DC input. These supplies are further categorized into constant voltage and constant current types, depending on whether they provide a stable voltage or current, with the current varying according to the load as described by Ohm’s law.

DC Power Supply

DC power supplies deliver either constant current or voltage and are categorized into linear regulators and switching regulators based on their control methods. They come in various forms, including benchtop and rack-mounted models. These supplies offer regulated DC power to components, modules, and devices, ensuring stable and precise voltage and current with minimal noise. Key settings on a DC programmable power supply include output voltage and current limit, which, along with the load, dictate the supply's operation.

A DC programmable power supply operates in two primary modes:

Constant Voltage (CV)

The output voltage is set by the user’s configurations, whereas the output current is determined by the load's resistance.

Constant Current (CC)

The Constant Current (CC) mode primarily serves as a safety feature but can also be used for other purposes. In this mode, the current remains fixed according to the user’s current limit setting. If the power supply operates in Constant Voltage (CV) mode and the current exceeds the set limit, it will automatically switch to CC mode. It will revert to CV mode once the load current drops below the specified limit.

The key parameters of a DC programmable power supply include maximum voltage, maximum current, and maximum power. These specifications ensure that the power supply can deliver the necessary voltage and current levels as required.

AC Programmable Power Supply

An AC programmable power supply provides alternating current to test equipment by simulating grid disturbances, such as interruptions, harmonics, and surges, which could potentially damage a Device Under Test (DUT). These supplies are utilized in various fields, including aerospace, lighting, laboratory testing, and military equipment production. They can generate alternating current at frequencies ranging from 45 Hz to 500 Hz, producing various waveform types like surges, traps, and dimmed phase waves to replicate different electrical scenarios.

AC current typically follows a sine wave pattern, where the amplitude represents the voltage and the frequency is measured in Hertz (Hz). The characteristics of sine waves can vary depending on the regional standards around the world.

Benchtop Programmable Power Supply

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.

Benchtop programmable power supplies are essential tools for electrical engineers and circuit designers, used to test and measure various electrical devices, including circuit boards and other electronic components. These supplies can be configured with either a single channel or multiple channels, where a single-channel model provides one controllable output, while multi-channel models may offer three or four controllable outputs.

In addition to channel differences, benchtop power supplies vary in polarity. They can be bipolar or unipolar: bipolar supplies can deliver both positive and negative voltages, while unipolar supplies are limited to positive voltages. Unipolar supplies can simulate negative voltages by reversing the leads.

Benchtop programmable power supplies typically fall into two categories: linear and switching. Linear power supplies are generally heavier, larger, and less efficient, but they offer high accuracy and minimal noise. In contrast, switching power supplies are compact, lightweight, and capable of delivering significant power, though they produce higher frequency noise.

One notable feature of some benchtop programmable power supplies is their ability to emulate battery behavior. These models can include an option for internal resistance, which mimics the behavior of a resistor in series with the positive output terminals, thereby simulating battery operation.

Like most programmable power supplies, benchtop models can be set to operate in constant current or constant voltage modes.

Rack Mounted Programmable Power Supplies

Rack-mounted programmable power supplies are designed to be installed in a support rack, where multiple units can be stacked together. These supplies can function as standalone units or be interconnected to provide higher voltages or currents to multiple devices. They support various operational modes, including constant voltage, constant current, and constant power, similar to other types of programmable power supplies.

Control features for rack-mounted programmable power supplies include slew rate adjustments, arbitrary waveform generation, and internal resistance simulation, much like benchtop models. Additionally, they offer display brightness controls, which are crucial for visibility in a rack setup. An important aspect of these supplies is their remote control capability, with options for LAN, USB, and built-in analog interfaces.

Typical rack-mounted programmable power supplies offer an output range from 200 W to 15 kW. By paralleling multiple units, it is possible to achieve a combined output of up to 60 kW with voltages reaching up to 1500 V.

Chassis Mounted Programmable Power Supplies

Chassis-mounted programmable power supplies are installed into a chassis or frame and come in both linear and switching models. These supplies convert AC current to DC current based on the application's requirements. The chassis can take various forms, with controls typically located on the front panel of the chassis.

Chassis-mounted power supplies come in several configurations, including enclosed, U chassis, and L chassis models. U chassis models feature an open frame and can be equipped with or without a cover. They are designed for efficient thermal dissipation, electromagnetic compatibility (EMC) protection, and offer flexible mounting options.

Enclosed models have their components mounted on a base PCB and are housed within a protective case. These enclosures, which can be made from metal or other materials, are designed to ensure safety and shield internal components from external interference. While open-frame power supplies offer certain advantages, they lack the protective features and safety provided by enclosed models.

Digital Programmable Power Supply

Digital programmable power supplies offer precise control and monitoring via a digital interface and encoder knob. Specifications are input digitally and converted into data that is used by the converter. After entering the parameters, the power supply calculates the necessary compensation factor to establish the pulse width modulation (PWM) duty cycle and generate the output waveform.

Analog Programmable Power Supply

Analog programmable power supplies utilize knobs and dials for adjusting output parameters. Although they are generally less precise than digital models, they are valued for their simplicity and suitability for specific applications. The analog control circuit provides feedback to the primary control system using traditional voltage and current sensing methods, error amplifiers, and optocouplers, which are semiconductors allowing signal transmission between circuits.

For applications requiring specific input, output, wattage, and form, analog programmable power supplies are an excellent choice. Their analog controls are stable, reliable, and exhibit fewer issues or glitches compared to digital counterparts.

However, analog programmable power supplies have limitations in flexibility. Adjusting settings necessitates changes to the power supply's design, making them less adaptable. While they are dependable and suitable for situations where settings remain constant, they lack advanced monitoring and control features found in digital models. They are ideal for stable applications but less effective for scenarios requiring frequent adjustments.

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Chapter Four: What are the differences between linear and switched programmable power supplies?

Programmable power supplies convert electric power from their input source to deliver to the load. The input and output can be either AC or DC current. DC current, which flows consistently in one direction, is typically preferred for electronic devices. Conversely, AC current is used for power transmission through lines and alternates direction periodically.

Programmable power supplies come in various types, each designed and configured to meet the requirements of different electronic devices and applications. They are programmed with the necessary parameters to achieve the desired performance.

These power supplies continuously monitor and adjust the output voltage to maintain the specified value. They also include additional controls for setting current and voltage limits, filtering noise, and adjusting output. The primary types of programmable power supplies are linear and switching models, with linear power supplies being simpler and less complex.

Linear Programmable Power Supply

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.

Linear power supplies have been in use for many years and represent one of the earliest types of power supplies. With the advent of new controls and technological improvements, linear programmable power supplies have been updated to meet modern requirements in the 21^st century.

Compared to switched programmable power supplies, linear models feature larger and heavier components, which can make them bulkier and generate more heat. Despite their improved accuracy, linear programmable power supplies are approximately 50% less efficient than their switched counterparts.

Linear programmable power supplies are ideal for applications demanding precise regulation, minimal ripple, low electromagnetic interference, and superior transient response. They reduce input voltage to achieve a lower output voltage. This voltage adjustment is accomplished through a transformer that steps down the voltage from an AC source to a lower AC voltage, which is then converted to DC voltage via rectifier circuits and filters.

Switched Programmable Power Supply

Switched programmable power supplies are advanced and versatile devices that offer greater efficiency compared to linear power supplies. Despite their complexity, they are typically smaller, lighter, and more cost-effective than linear models.

One key advantage of switched programmable power supplies is their minimal power loss across the switch due to their high-frequency operation. However, this high frequency can generate noise that may affect other circuits. This drawback is offset by their broad input voltage range and high output capability, which enhance their overall efficiency.

Despite their benefits, switched programmable power supplies come with challenges, including complex circuitry, potential interference with AC mains, elevated noise levels, and the need for shielding to manage their high operating frequencies.

The widespread adoption of switched programmable power supplies is driven by the trend toward smaller, more portable electronic devices. These power supplies use semiconductor technology to regulate and convert power by rapidly switching on and off.

The different types of switched programmable power supplies include:

• Forward Converters
• Self-Oscillating Converters
• Flyback Converters
• DC to DC Converters

Programmable Power Supplies for Batteries

Traditional power supplies offer fixed settings with limited options for adjustments, whereas programmable power supplies provide enhanced flexibility with multiple modes. Users of programmable power supplies can adjust various settings, such as voltage, current, power, and operational modes, according to their specific needs.

Controlling these parameters offers several advantages, including:

• Applications with unknown or variable voltage requirements
• Unique voltages not found in standard voltages
• Being able to vary voltage during a process
• The ability to change modes between processes

With a programmable power supply, a battery charger can initially provide a constant current during the early stages of charging and then transition to constant voltage (CV) as the battery approaches full charge. If the current exceeds the limit while in CV mode, the power supply will automatically revert to constant current (CC) mode. In CC mode, the programmable power supply maintains the current at a set level, ensuring safe operation. The output current and voltage are regulated according to user-defined settings.

Chapter Five: What are the key components of a programmable power supply?

A programmable power supply consists of several key components, including a transformer, rectifier, filter, and regulator circuits. These components work together to ensure a stable power supply for multiple devices and are essential for experiments where precise control of current and voltage is required.

Transformer

In a programmable power supply, the transformer is a static component that transfers electrical energy from the primary winding to the secondary winding without altering the frequency. It is used to either step up or step down the AC voltage. Additionally, the transformer provides isolation between the electronic system and the AC power source.

The primary winding of the transformer connects to an AC voltage source, while the secondary winding connects to the load. Although energy is transferred from the primary to the secondary winding, the two are electrically isolated from each other. This energy transfer occurs through electromagnetic induction, which generates a voltage in the secondary winding.

The transformer in a programmable power supply serves three main functions: adjusting the voltage level (either stepping it up or down) and providing electrical isolation between the primary and secondary circuits.

Rectifier

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

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

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.

Full Wave Bridge Rectifier

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.

Filter

In a programmable power supply, the filter is crucial for removing ripple components from the output. It transforms pulsating DC current from the rectifier into a stable, smooth DC voltage. There are two main types of filters used: capacitance (C) filters and resistor-capacitor (RC) filters.

C filters are the most basic and cost-effective type of filter. RC filters, on the other hand, are employed to further reduce ripple voltage that persists after C filters, allowing for the passage of the DC component. RC filters work by blocking certain frequencies while permitting others to pass. They come in two varieties: high-pass filters, which allow signals above a certain cutoff frequency to pass, and low-pass filters, which permit signals below a cutoff frequency to pass.

The primary role of filters is to control the ripple factor, which represents the unwanted AC component remaining after rectification. This ripple can potentially harm the load, so filters are designed to smooth the signal and attenuate the AC component. The ripple factor is calculated as the ratio of the root mean square of the ripple voltage to the DC component of the output voltage, and is often expressed as a percentage. Evaluating the ripple factor helps determine the filter's effectiveness.

Voltage Regulator

The primary function of a programmable power supply is to deliver a stable output voltage to ensure proper operation of the connected load. This output voltage must remain constant despite fluctuations in the input voltage. Voltage regulation is achieved using two main types of regulators: series voltage regulators and shunt voltage regulators.

A series voltage regulator manages the unregulated input voltage that is delivered to the output. It employs a feedback circuit to sample the output voltage, which is then compared to a reference voltage by a comparator circuit. This feedback mechanism helps maintain the desired output level. In contrast, a shunt voltage regulator diverts current away from the load to regulate the output voltage.

Integrated circuits (ICs) used in programmable power supplies typically include a reference source, comparator, amplifier, control device, and overload protection. These components work together to control the output values, which can be adjusted by the user to meet specific requirements.

Chapter Six: What are some of the top programmable power supplies available?

ITECH IT7321 Programmable Power Supply from Circuit Specialists

The ITECH IT7321 employs linear amplification to generate output signals that closely replicate the input. It is particularly valued in avionics for meeting stringent testing standards required for aviation electronics and for its capability to operate at 400 Hz AC during evaluations. The ITECH IT7321 facilitates precise, high-resolution testing, making it a reliable tool for accurate and efficient testing procedures.

PLS Series Programmable DC Power Supply from DigiKey

The PLS series single-output programmable DC power supply provides a range of DC output voltages, including 30V, 50V, 100V, 200V, and 400V, with power ratings between 600 W and 1500 W. This versatility allows users to achieve various voltage and current settings from a single unit. The PLS series supports operation in series, parallel, or combined configurations, enabling output voltages up to 800V and power up to 6 kW. It also offers remote control options through USB, Ethernet, and analog inputs.

EDU36311A Bench DC Power Supply from Keysight

The EDU36311A is a compact triple-output power supply designed to fit comfortably on a workbench. It features a 7-inch color display that allows for simultaneous monitoring of all outputs. Each output is independent, enabling configurations such as series connections for higher voltages, parallel setups for increased current, or stacking. The EDU36311A includes a sequencing function to enable or disable outputs in a predetermined sequence, and its control logic can be configured before applying power to a device. Additionally, the unit comes with proprietary software for remote control and data logging capabilities.

Sequoia Series Precision Programmable Source from AMETEK

The Sequoia series is a versatile four-quadrant regenerative grid simulator, optionally equipped with a regenerative electronic load mode. This series offers high power capabilities and flexibility, making it an advanced solution for AC applications. Featuring SIC power switching technology, the Sequoia series is designed with a compact and durable floor-standing chassis. It provides an easy configuration for both single and multiphase AC power, as well as single and multichannel DC power. The Sequoia series is suitable for applications including power conditioning, grid-interactive green energy systems, and power distribution generation.

GENESYS+™ Programmable Power System from TDK-Lambda

The GENESYS+™ is a portable and user-friendly programmable power supply, known for its lightweight design and multifunctional front panel. It features isolated analog and optional communication interfaces. Available in power levels of 30kW, 45kW, and 60kW, the GENESYS+™ is housed in a 23U rack system profile. A key highlight of the GENESYS+™ is its low-noise output, with voltage ranges from 10V to 600V. It supports AC input options, including built-in active power factor correction, with choices of three-phase 208 VAC, 400 VAC, or 480 VAC. Additional features include programmable slew rate control, constant power limit control, an arbitrary waveform generator with auto-trigger functionality, and internal resistance programming.

Chapter Seven: How to Choose a Programmable Power Supply?

Programmable power supplies offer a wide range of applications and are crucial for testing, diagnosing, and safeguarding electrical devices. Choosing the right programmable power supply involves evaluating key factors to ensure it meets the requirements for effective use.

Voltage and Current Ranges

Choosing a programmable power supply starts with assessing the voltage and current requirements of your application. The output specifications must align with the testing needs or power demands. It's crucial for the power supply to handle both maximum and minimum values without compromising precision or safety. Excessively high voltage or current settings can negatively impact the accuracy of the output.

Programmable Features

The appeal of programmable power supplies largely stems from their diverse range of controls and data feedback options. Key features include the ability to set voltage and current limits. While many models offer remote control capabilities, it's important to consider the type of remote interface available. Additional common features include ramping, sequencing, overcurrent and overvoltage protection, electronic current limiting, and thermal resets.

Output Stability

Output stability denotes a programmable power supply's capability to maintain stable voltage and current levels despite varying load conditions over time. This characteristic is detailed in the power supply's specifications, which cover load and line regulations to indicate its stability performance. For applications requiring precise and stable power output, selecting a power supply with high stability is essential. The final choice should align with the specific needs of the application.

Number of Outputs

Multiple outputs enhance efficiency and allow for connection of several loads to a single programmable power supply. When selecting a power supply with multiple outputs, ensure each output is isolated and can function independently or in parallel to provide greater flexibility.

Output Enable and Disable

This feature, while optional, is generally recommended as it allows users to turn outputs on or off without interrupting the load supply. It facilitates setting up different tests without concerns about their impact on the load.

Constant Current and Constant Voltage

Constant voltage is a standard feature in all programmable power supplies, designed to provide stable voltage while varying the current for testing. Occasionally, switching to constant voltage mode is necessary for applications requiring stepped voltage sequences.

Easy Setup

An easy setup process for a programmable power supply allows more time for testing and monitoring applications. Many programmable power supplies feature intuitive controls that facilitate quick and efficient setup. Units with separate controls for voltage and current and fine-tuning options offer enhanced precision.

Cooling

Effective temperature management is crucial for the reliability and safety of a programmable power supply. It is highly recommended to choose a power supply with an integrated high-performance cooling system. Various cooling designs are available, each suited to specific types of programmable power supplies.

Conclusion

• A programmable power supply is a method for controlling output voltage using an analog signal that is controlled by 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 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.
• The classifications of programmable power supplies are first divided by the type of current they monitor and control.
• 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.
• 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.

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