Linear Regulation

The principle of operation of a linear regulation power supply is shown in the following diagram:
Linear Regulation

The input voltage comes from a transformer, full-wave rectifier, and filter capacitor stage. The output voltage is compared to a reference voltage (derived, for example, from the front-panel settings of the power supply) and the difference is fed to the transistor to allow more or less current through it. The transistor is usually a bipolar or MOSFET type (sometimes as part of a control IC for smaller supplies) and is operated in its linear region (hence the name, “linear” regulation). The linear regulation strategy has advantages of simplicity, low noise, fast response time, and excellent regulation. A disadvantage is that they are ineffective, as they are always dissipating power. In the above design, you can see that the transistor has Vin – Vout across it. Multiply this difference by the current to get the power being dissipated. For a large voltage difference (i.e., low power supply output voltage) and large current, the overall efficiency can drop down to nearly 10%. The maximum efficiency for a linear supply is generally around 60%. Typical average efficiencies are in the 30-40% range.

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[...] to power the scope or use a differential amplifier to measure the normal-mode noise. Ripple for linear power supplies is usually measured at twice line frequency. For switching power supplies, you’ll want to [...]

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