Choose PSU that can handle back emf from motors

[nour]

I am not sure how to start this question, but I am trying to run 4 stepper motors with from 48V DC source each
It is Sanyo denki 103 - H7823 - 1741 bipolar motor, the specs as following:

Current 4A
Resistance 0.65R
Induction 2.4mH
Back E.M.F 75 V/Krpm

I want to know how to choose a proper Power supply to handle the motor back emf?

I read somewhere that the power supply should be able to handle the back emf so it wouldn't go through the drivers and other electronics!

I really do not understand this point, can someone explain how a power supply would or would not be able to handle the motor's emf?

[Srbel]

I would just use a flyback diode?

[Kleinstein]

You need free wheeling diodes to direct the current from back EMF to the supply. The usual driver circuits have that. The supply must be able to take up the extra current, that otherwise would raise the voltage too high. Usually just sufficient capacitance at the supply is enough.

Usually the main source is just the inductance, so the energy is rather limited: here E = 0.5 I²*L = 19,2 mJ. So not really much. At 40 V, that is only some 0.5 mAs or 0.5 V rise in a 1000 µF capacitor. Due to losses the actual energy will be lower. So something like a 1000 µF capacitor and a supply / driver that can stand a 1 V voltage rise should be enough.

The only exception would be, if the motor really has to work as a generator to slow down heavy parts. Than you might need a sink for the energy, e.g. a 2 quadrant supply or an extra circuit for over voltage limitation (e.g. a kind of power zener diode at 50 V).

[Zero999]

an extra circuit for over voltage limitation (e.g. a kind of power zener diode at 50 V).

TL431 + some chunky power transistors.

[nour]

Thanks for the contributors.
So basicly what I have understood if the output of a power supply have enough capacitance it would be ok, is that right ! 

[Kleinstein]

The capacitance is Ok to cope with the magnetic back EMF. So if the motor is not running very fast (e.g. less than 500 RPM, so it would normally not go up to the supply level) and does not need to break a heavy load fast, the capacitance is enough. But if the motor is really converting significant mechanical energy to electricity more (like the active sink / clamp circuit) might be needed. The limit somewhat depends on the driver and details on how fast it runs / stops.