Difference between Linear Supply and Switch Mode Power Supply


The linear power supply and Switch mode power supply, both supplies DC power to electrical and electronic circuits but the similarities end here. The crucial factor which differentiates linear power supply and SMPS is the working procedure. The Linear power supply converts high voltage AC into the low voltage using a transformer and then converts it into DC voltage while the switched mode supply converts AC into DC first then transform that DC voltage into desired voltage.

Key Differences Between Linear Supply and Switch Mode Power Supply

  1. The main difference between the linear power supply and SMPS is that linear power supply converts the high voltage of AC into low voltage AC first then the rectification procedure takes place. On the contrary, the SMPS converts the AC signal into DC signal first then the stepping down of voltage signal takes place.
  2. Linear power supply use voltage regulator for voltage regulation of the output voltage while SMPS uses feedback circuit for voltage regulation.
  3. Power dissipation also plays a key role in differentiating linear power supply and SMPS. The Linear power supply also dissipates power and thus requires a heat sink, but SMPS do not requireheat sink as there is no power dissipation.
  4. The step-down transformer used in linear supply is bulky while in SMPS the step-down transformer is light in weight.
  5. The noise disturbance is more in SMPS due to switching action; this makes SMPS inappropriate for audio and radio frequency application. The linear power supply is immune to noise disturbance and thus used in audio and radio frequency application.
  6. There is the major difference between the efficiency of the linear power supply and SMPS. The efficiency of the linear power supply is low about 20-25% due to ohmic losses while that of SMPS is high, i.e. about 65-75%.


The linear power supply steps down the AC voltage first then converts it into DC while SMPS converts into DC first then uses the step-down transformer to obtain the desired voltage. The SMPS has the drawback that it creates noise interference due to switching. Moreover, switching also creates electromagnetic interferences and RF interferences thus EMI filters, and RF shielding is also used along with SMPS circuit.