What is a "Switching" power supply?

[EvanRobert]

Hi All,

I've read a few places on the web about motors or drivers not working well with "Switching" power supplys.

Why?

Thanks,

Evan R.

[HuFlungDung]

Hi Evan,

I think that switching refers to the method of rectification of the AC supply to make DC. Somehow, the power supply outputs a series of pulses that simulate a DC current. The waveform is not dead smooth like true DC, but is chopped.

A PWM amplifier runs on this chopped DC, I believe.

If you go for a real DC power supply to feed your amplifiers, you will get around the choppy DC problem.

I believe that the motor needs to possess a certain amount of inductance to smooth over the jaggedness of the "switched power" supply. Motors will typically have a rating in millihenrys or microhenrys that give you a ballpark figure to compare with the specs of the motor load recommended for a given power supply.

Balsaman might know more about this stuff

[balsaman]

As far as I know Hu is correct. A switching supply often doesn't use a transformer. PC supplies are switching supplies. There are filters and such to smooth the DC tho and to my knowledge a switching supply works fine for steppers and such. Perhaps the performance is not optimal, I am no expert on the subject. I used a PC supply on my first router with great success, as have many others.

Eric

[Mariss Freimanis]

Switching power supplies rectify the AC line voltage and filter it at about 320VDC (voltage doubler rectifier). This DC voltge supplies a pulse-width regulator that operates at 40 to 100kHz. The high frequency is passed thru a transformer and is rectified back into a DC voltage.

Why do all that? Transformers are much much smaller at high frequencies and the pulse-width "switcher" regulates the output voltage without generating heat the way a linear regulator does.

The result is a small and light power supply, often less than 10% the size of an "iron" power supply (xformer, rectifier, filter cap). If a linear voltage regulator is used with the "iron" supply then the heat generated can be enormous, a problem the "switcher" doesn't have.

Mariss

[EvanRobert]

Thank to everyone.

Now, I understand well enough to move on t the next step of building.

Thanks,

Evan R.