Linear vs Switching Power Supply

[EET]

I believe this is a simple question. I would like to know the basic difference in linear and switching power supplies and the pros and cons of each.

Thanks in advance.

 

[Lewish]

In a linear supply, the output voltage is maintained by an electronically variable resistor. Usually a power MOSFET.
Pros: - simple design, cheap, little electrical noise.
Cons: - lots of waste heat, lots of waste heat, can be slow to respond to transients, usually larger than switchers for the same power rating.

In a switching power supply the output voltage is controlled by varying the percentage of time the controlling switch is on.
Pros: - usually much smaller than a linear of the same power rating, can have very good transient response.
Cons: - more complicated to design and get to work as desired, lots of electrical noise that should be dealt with.

That is a quick and simple answer.

 

[peebee]

On AC to DC converters:

Linear power supplies typically rectify (by switching at the fundemental frequency) and filter the AC source. Ripple current will be at the same fundemental frequency as your AC source. Big capacitors are required to support the voltage and reduce ripple. Transformers are required if your AC and DC RMS voltages are not roughly equal.

Switchmode power supplies essentially interrupt the current through an inductance to generate voltage, or switch an AC source into a capacitance to maintain voltage. Changing the duty cycle changes the voltage. Switchmode power supplies can operate at frequencies much higher than the AC fundemental. The higher frequency means that smaller coils can be used. Higher frequencies also mean smaller ripple voltage of a higher frequency that can be filtered using smaller capacitances. Impressive voltage changes can be accomplished using switchmode power supplies without requiring transformation (although transformation may offer other benefits, such as isolation from the line).

They will both impose ugly harmonics onto your power supply without input filtering.