Engineering Definitions
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Switching Regulator

A device that utilizes a series switch which will open and close to control the flow of power to the output load. Following that basic definition; the average output voltage is proportional to the ratio that the switch is closed to the switch being open [which would be the switch duty cycle].

The graphic below shows the schematic diagram of a positive output switching regulator IC. The input voltage is input to pin 4 and the regulated output is taken from pin 1, note the LC filtering applied to the output signal. The switching voltage is applied to pin 3.

Positive Voltage Switching Regulator
DC/DC Switching Regulator Schematic

Some switching regulators also have an external pin for feedback, and may also have an internal oscillator instead of an external pin for switching. Of course except for the polarity change[s], the schematic would appear almost identical if it were showing a negative voltage regulator.

Switching Regulator. A regulator that converts the incoming DC to a switched voltage applied to a transistor or FET with a feed-back path to keep the output voltage constant. A standard 4-terminal regulator is shown above consisting of a input terminal, and output terminal a switch input and ground.

Switching Regulator
Switching Regulator Construction

One example of the internal structure of a switching regulator. Note the input and outputs referenced to ground and the switching input pin. A 4-terminal leaded metal can is shown below as a possible package [one of many possible].

Switching regulator are common because many times they're smaller than their analog counter parts. However switching regulators do have a draw back, the clock used to switch the regulator generates noise. In some cases that noise is carried out though the output and passed to the circuits being powered by the regulator. So care needs to be taken when using a switching regulator. The regulator needs to be filtered well and should be layed-out on the board with care. Switching regulator should never be used to power noise susceptible devices like A/D, D/A converters or low noise amplifiers. The clear alternative would be to use a linear regulator.

Related Terms for switching Regulators.

Inductor-less DC/DC Regulators. Charge Pumps.

Integrated Switch. Another name for a switching regulator, without a controller.

Noise. Because switching regulators use a square-wave to turn the regulator on and off they tend to generate noise. The noise could pose an issue with sensitive analog circuits. Precautions should be taken to reduce the chance that noise interferes with the rest of the circuit [see switching noise design below].

Non-Isolated Switching DC/DC Regulators. Text in review

Package Type. The case used to house the regulator. Any package style is possible, a 4-Terminal TO72 is shown as an example.

Pulse Width Modulator Regulator. PWM Regulator

Point-of-Load Regulator [Controller]. Also called a Point-of-Source Regulator. A regulator that resides next to the component receiving the output voltage. Basically any regulator could be referred to as point of load regulator, as long as it sits next to device receiving the power. In fact some engineers may refer to a regulator located on a Printed Wiring Board as Point-of-Load Regulator, in a multi-card design.

Switching Noise Issues

The general recommendation is always begin a design and certainly the circuit layout with noise issues in mind. Separate noise generating devices from noise sensitive devices. Use separate power or ground traces to reduce the chance that noise is coupled into other circuits. Of course always use ground planes if possible to reduce the impedance of the ground plane and insure noise signals are shunted off the board. A few additional System Level EMI Protection ideas are provided.

PC motherboard

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