Linear Power Supply Noise

Linear Power Supply

Prior to the digital age all DC power supplies were linear. A linear power supply contains a transformer that reduces the input AC voltage to the required DC output voltage. The low AC voltage is directed by a diodes bridge and filtered by a capacitor.

Unlike switching power supplies, linear power supplies generate very low ripple noise most of which is at the AC input frequency.  The conducted emission, radiated emission, common mode noise and the leakage current are low compared to a switching power supply. Linear power supplies have many disadvantages:

  1. Weight, dimension and price – the transformer that reduces the input voltage operates at the AC input frequency which is either 50 or 60 Hz. Transformers at low frequency are expensive, heavy and large compared to transformers for high frequencies which switching power supplies use. This makes a linear power supply large, heavy and expensive compared to a switching power supply.
  2. Narrow AC input range – Electrical instruments need a flexible AC input range in order to operate the same in different countries with different AC power voltage and frequencies. 1115V 60Hz Vs 230V 50 Hz. Linear power supply AC input has a very narrow range that limits its use.

Linear Power Supply circuit diagram

Linear Power Supply circuit diagram

Linear Power Supply Ripple Noise Waveform

Linear Power Supply Conducted Emission

Linear Power Supply Radiated Emission

Linear Power Supply Common Mode Noise

A DESKTOP LINEAR POWER SUPPLY

desktop linear power supply
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