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What is a power supply?

Latest Updated:07/01/2006

Question:

What is a power supply?

Answer:

Personal computers, AV equipment, and other common electronic devices incorporate a number of electronic components in order to realize the functions of those devices. "Power supply" is the name given to the functional block that supplies the voltage or current required to operate the electronic components.



Broadly speaking, the power supply block performs the following two functions.

- Converts alternating current to direct current
- Converts direct current to direct current

These functions are explained below.

1. Conversion of alternating current to direct current

[Why conversion is necessary]
The electricity supplied to this power supply block is the electricity that is supplied from the power station to the power outlets of the office or house where the electronic device is being used. This electricity is 100 V AC in Japan. On the other hand, most of the components in an electronic device operate on direct current and a low voltage (such as 3.3 V or 1.8 V). In other words, the alternating current from the power outlets must be converted into direct current in order for the electronic device to operate.

For more information on alternating and direct current, see "Please explain the meanings of the units used to measure electricity" in the Electricity section of the Basic Knowledge FAQ.

[Role]
The role of the power supply block is to convert the alternate current from the power outlets into the direct current required by the electronic components.
The power supply IC in this power supply block is used to convert the rectifying circuit output to the required stabilized DC voltage.



2. Conversion of direct current to direct current

[Why conversion is necessary]
These days, consumers are demanding smaller and more power efficient electronic devices. This means that the power supply block must also be more compact and reduce power consumption and heat. Switching power supplies have been developed to satisfy these demands.
The electricity supplied from another source such as a battery is limited to a specific DC voltage (for example 12 V) and such supply situation is unstable. On the other hand, the various electronic components incorporated in electronic devices require different voltages (for example, 3.3 V and 1.8 V), accuracies, and capacity of currents, and abovementioned power source does not satisfy these power supply specifications of electronic components. Therefore, here too, conversion is required.
For more information on switching regulators, see "System Differences" in the Types of Power Supply ICs section under Power Supply IC in the Linear IC FAQ.




[Role]
The power supply block also has the function of converting the unstable voltage supplied from the battery to the stable voltage required by electronic components. A switching regulator, which is one type of power supply IC, can reduce heat generated by the conversion.
In the DC-DC conversion diagram shown in the next figure, the power supply IC has the function of converting the unstable DC voltage including ripples into the required stable DC voltage.

Suitable Products
Power Management Linear