This tutorial installment is: The Achille’s Heel of Electronics Products. The power supply often becomes the Achille’s heel of electronic product design. Why?

This topic answers the following questions about power supplies:

• What are the pitfalls of their implementation?
• Why are they the system weak link?
• When is the best time to develop system power requirements?
• What is the correct perspective with which to approach their implementation?

To view a different topic, go to the Power Supply Tutorial table of contents.

Last topic: What is a Power Supply?

Next topic: Unregulated Power Supplies

Pitfalls of Power Supply Implementation

• Assuming that it is a perfect black box: Supplies are less than perfect devices. Not only do converter characteristics and performance affect the load operation, but the load characteristics also affect converter behavior. The same type of interaction also exists at the input of the converter with the source. Finally, the load characteristics can be indirectly reflected to the source through the power supply and vice versa.
• Assuming that it is a simple aspect of product design: Converters are often not simple. The design of converters will usually go beyond the skill set of most non-power electronics engineers. Even the application of off the shelf conversion devices can be a challenge as the documentation that accompanies them is usually limited, with little disclosure about the internal design which may significantly impact compatibility with loads and sources.
• Allowing it to be an afterthought in the design process: Since the power supply is not a perfect black box, it cannot be relegated as an afterthought in the design process. Product design must take place keeping converter capabilities in mind. Otherwise it is possible to design a great product, but have no power supply for it.
• Failure to allocate adequate physical space for it: Conversion devices need space. While technology for improving efficiency is continually improving allowing for smaller supplies, it is a mistake to not plan for space for converters.
• Failure to adequately specify the important performance requirements: There are numerous specifications which a power supply must satisfy. If they are not identified, poor performance is the likely result.

The Power Supply is Usually the Weak Link

Conversion devices are usually the weak link in most electronics products and usually will be the first components to fail. The stress levels on the internal conversion components are usually much higher than in other electronics components. Forms of stress include voltage, current, power, and temperature. All of these forms of stress have major impact upon component reliability and lifetime. Therefore, reliability of the product is usually dominated by the power conversion choice. For this reason and others, the converter must not be relegated as an afterthought in the design process.

When to Develop the Power Supply Design Plan

The plan for implementation should be developed before the product design review which is a critical milestone to be completed before hardware is built. There must be confidence that a reasonable approach exists before committing to hardware. Not completing this vital check in a product design is an invitation to disastrous results, cost overruns, and schedule delays. Don’t fall into the trap of assuming that the power supply is a trivial component. They usually are not. Identifying the specifications should be an important of the plan. Please download the Applications and Specifications Requirements Form.pdf for help with this task.

The Correct Perspective for Power Supply Implementation

The power converter must be seen as a critical component in the system. Without a thoughtful  implementation, the system will perform poorly at best. Remember that there are usually significant interdependencies between the power supply and the load and the source. Treating it as a black box or as an afterthought will usually lead to late stage and costly surprises. Finding the cheapest implementation usually leads to poor value and prototyping troubles. Put extra effort to seek the best value which is a compromise of low cost, outstanding performance, small size, and reliability. These factors are typically weighted according to their relative importance in your application.

Next Topic

The next tutorial installment is: Unregulated Power Supplies. This next topic will answer the following questions:

• What are unregulated power supplies?
• What are the basic types of unregulated power supplies?
• What are the advantages and disadvantages of unregulated power supplies?

If you need assistance with power electronics design, call or email us today for help with your requirements. You can also go to our power electronics consultant website for more information about our services for business clients. Thank you for reading this tutorial article entitled “The Achilles Heel of Electronics Products”

Next topic: Unregulated Power Supplies

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This tutorial installment is: What Is A Power Supply? This topic answers the following questions:

• What is a power supply?
• What are the types of power supplies?

To view a different topic, go to the Power Supply Tutorial table of contents.

Last topic: N/A

Next topic: The Achille’s Heel of Electronics Products

What Is A Power Supply?

The term “power supply” is a misnomer.  Power supplies do not create or supply power. Rather, power supplies are electronic or electrical equipment which change the form of available energy into a form useful to equipment. Some examples of sources of electrical energy are: wall outlets, solar panels, batteries, and wind. A more recent technology is energy harvesting – energy extraction from our environment around us. The process of changing electrical energy form is called power conversion and a better term for “power supply” is “power converter”.

For example, in the typical home, power is available at electrical wall outlets in the form of 120 volts, 60 Hz alternating current (in the United States). This means that electrical current with RMS amplitude of 120V is constantly reversing in direction 60 times per second. This is the form of electrical power generated by rotating machinery at the utility company.

But this form of electrical energy is not directly useful for electronic equipment which typically requires a constant voltage level of some amount, perhaps 12 volts direct current. The role of the power supply, in this case, is to change the form of electrical energy available from the wall alternating voltage to a constant voltage at 12 volts.

Types of Power Supplies

The basic types of power conversion are:

• AC to DC:   rectification, ex: 120VAC to 12VDC and 5VDC rectifier for a desktop computer
• DC to DC:  conversion, ex: 9VDC to 5VDC converter to change the voltage from a 9V battery to 5V for use by common electronics
• DC to AC:   inversion, ex: 12VDC to 120VAC inverter to generate AC for appliances from a car battery
• AC to AC:   cycloconversion, ex: 120VAC, 60Hz to 115VAC, 400Hz cycloconverter for military use

Power supplies can change voltage up or down, rectify voltage, provide isolation, provide a constant current, provide a constant power, or frequency.

They can also be classified according to switching or linear type. A switching supply uses high frequency switching and energy storage devices such as inductors and capacitors to chop the incoming energy into small building blocks and then recompose the building blocks into the required form for use. A linear supply uses a series element such as a pass transistor to absorb the unneeded energy that is not used by the load. A switching supply is generally light and efficient, but the input current and output voltage cleanliness is not so great. A linear supply produces very clean output voltage, but it is generally large and heavy.

Next Topic

The next tutorial installment is: The Achille’s Heel of Electronics Products. This next topic will answer the following questions:

• What are the pitfalls of power supply implementation?
• Why is the power supply the system weak link?
• When is the best time to develop system power supply requirements?
• What is the correct perspective with which to approach power supply implementation?

If you need assistance with power electronics design, call or email us today for help with your requirements. You can also go to our power electronics consultant website for more information about our services for business clients. Thank you for reading this tutorial article entitled “What Is A Power Supply?”

Next topic: The Achille’s Heel of Electronics Products

Back to table of contents.

The post Tutorial: What Is A Power Supply? appeared first on POWER ELECTRONICS CONSULTANT.