Tutorial: What Is A Power Supply?

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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?

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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

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