Regulated vs. unregulated Power Supply?

[Ferny]

Why do stepper drives use unregulated supplies?

[jerber]

They don't.

I use a regulated (switching) supply.

[neilw20]

If you use a Switchmode supply, it will almost surely be regulated.
A transformer, rectifier and filter capacitor is un-regulated.
Micro-stepping Stepper Drivers are a current regulated device, based on output load characteristics, which changes with rotational speed of the stepper.
Because they are a current regulated device the only point in having a regulated supply is so that you don't exceed the maximum input rating of the stepper controller.
A 60v maximum voltage rated controller will usually be run on 48v.
36v AC from a transformer rectified and filtered will give you close to 48v DC.
(36v - 1.2v) * 1.414 = 49volts. The 1.2v is the voltage drop in the rectifiers.

[pastera]

Two reasons

#1 - cost: the drives do not need a regulated supply and at the power level involved regulated supplies get expensive. The drives are there to regulate the power supplied to the motor so any preregulation is wasted

#2 - Regeneration: stepper drives send energy back into the supply when slowing down the motor. Most switching supplies cannot handle this and will be destroyed rather quickly. A supply that can handle this issue brings you back to reason #1

Aaron

[Ferny]

I was just wondering.
We always use regulated switchers at work but they also power up other electronics. I have NEVER had switcher blow up running a stepper drive in the last 10 years. We must use the good ones. I have seen plenty of blown motor drive IC's from people unplugging powered up units though.

I figure they used unregulated PS's for a cost issue? I've read they can react faster?

Thanks,

Ferny.

[pastera]

A simple power supply (bridge + capacitor) can't react any faster than the line - if the transformer output voltage is less than the output voltage plus diode drops, the capacitor is not being recharged. So the unregulated supply can't be expected to react any faster than about 1/120 S.

A switching regulated supply usually will have an intermediate capacitor bank at a much higher voltage than the output which is charged by the line. The output bank is then charged at the switching frequency of the unit, usually well over 20KHz.

A linear regulator can be designed for very fast responce time but still has an itermediate voltage much higher than the output.


What kills the switchers is the output pumps up very fast because of the very low value of output capacitance. The same energy dumped into a smaller value of capacitance will result in a higher voltage. If you isolate the switcher with a diode and a small capacitor with a overvoltage shunt, it will be well protected and still much smaller than the same capacity unregulated (but still more expensive).
Aaron