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Electronics for CNC apparates

Last update: 31/07/2015

Normally a CNC machine is powered by two different voltages:

  • +5V for the logic (using a very low current, sometimes limited to few milli/microampere);
  • a voltage usually from 20-24V upto 80V to power the stepper motors (accordingly to the stepper driver used).

While it is really easy to purchase or to build a relatively high voltage power supply,  the main problem is how to obtain the +5V from the same source of the stepper motors power supply.

 

Many stepper controller/driver use particular ICs that include, in the same package, the translator and the power driver. Many of them have a max input voltage of 40-45V but there are a lot of controller/drivers that using discrete components can be powered by higher voltages, normally 60-80V, while the current needed to 'feed' the logic of the boards is generally very low (only few milliamperes).

To realize a +5V power supply for the logic, using the same power supply of the stepper motors, there are many different solutions:

  • source upto 18-24V: it is possible to use directly any voltage regulator (LM7805 for instance) because they have a max input voltage level around 32-35V (yes, we know, the declared maximum input voltage of a 5V regulator is referred to the difference between the input and the output voltage bu for safety this is usually considered 0);
  • source upto 40-45V: we can use a LM317HV (HV is important) that has a max input voltage of 60V, followed by a traditional positive regulator;
  • source upto 80-100V: we can use a cheap Texas TL783, for instance, followed by other regulators.

Other solutions regard the use of one of the many step down switching regulators (LM5007-LM5008-LM5010 by National for instance) that need only a limited external circuitry. The market offers hundreds of such a chip. 

 

National (for instance) produces a series of step down voltage regulators (switching) really interesting (LM5007, LM5008, LM5010). They can manage an input voltage upto 80-100V (depends by the chips) and provide the current necessary to power the logical sections of a cnc machine.Even in this case it is better to insert immediately after the schematics (for safety) a simple positive regulator (7805) to obtain the +5V voltage.

lm7805 Traditional voltage regulation to obtain a +5V fixed voltage from the main power supply. The max input voltage level depends by the regulator
   
lm317

Two stages: the first drops down the main voltage upto 12-18V the second (using the usual 7805) produces the +5V voltage.

Using a LM317HV the max input voltage is 60V (50 for safety) while using a TL783 the input voltage is higher, upto 125V (80-90 for safety).

   
lm5010
 

National (for instance) produces a series of step down voltage regulators (switching) really interesting (LM5007, LM5008, LM5010). They can manage an input voltage upto 80-100V (depends by the chips) and provide the current necessary to power the logical sections of a cnc machine.

Even in this case it is better to insert immediately after the schematics (for safety) a simple positive regulator (7805) to obtain the +5V voltage.

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