Re: [CAD_CAM_EDM_DRO] power supplies

In a message dated 11/29/2003 9:45:30 PM Central Standard Time,
loren_allison@... writes:
Can anyone tell me the difference between a switching power supply
and a linear power supply.
Loren: A "linear" is the simple kind that regulates simply by "wasting"
energy. The basic transformer/rectifier/filter provides MORE voltage than the
variable load needs, and the REGULATOR in the linear supply "drops voltage", the
amount of "excess". This "goes up" as heat (that's why the heat-sinks on most
supplies).

A "switcher", on the other hand, is at least theoretically much more
efficient, as it "chops" the excess voltage/current so that the wanted energy-out is
"averaged" by "pulse-width modulation" (controlling the relative WIDTH of the
pulses). Most switching supplies do this "chopping" at frequencies around 20
kHz to maybe 50 kHz. They are "electronically" much more complex than the
simple linear regulated supplies, as you can surely imagine. However, a switcher
produces much LESS heat in operation, and most have only very small
transformers, if any. So, "Galvanic isolation" from the AC power-line can be a factor
to watch for!

I understand even a well-made "chopper" can still transmit nasties (EMI) over
the output-DC, and this WILL cause untoward syntax in the loads which may be
sensitive to unwanted pulse-sources! Most (all?) modern PC power-supplies are
"switchers", but the load-range of PC circuitry is well-known to the
designers of those, and this load is "reasonable", so such EMI can be safely handled
in design. But when you go using a "chopper driver" for a servo (DC motor),
fed from a chopped DC-regulator, well, things can get funky fast. Best advice:
If you had to ask what the diff. is, stick with linear-only regulated
supplies for "motor stuff". For some, particularly stepper drivers, you usually
don't even NEED voltage-regulation, so long as component parameters are
"ballpark". I immediately admit total ignorance of these details re servo-motor
drivers/supplies!

Lotsa luck! Jan Rowland


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