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Electronics for CNC apparates

Last update: 31/07/2015

The STMicroelectronics couple L297 + L298 is probably one of the most popular couples to control bipolar stepper motors. Unfortunately the heating generated by the final stadium can be considered rilevant, particularly when the motor uses a current higher than 1,5A-2A/phase. A quick solution is the substition of the final dual full bridge (STM L298) with two full bridge (STM L6203).

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.

This is the traditional couple of ics widely used all over the world to drive a small (up to 1.5-2amp/phase) bipolar stepper motors. Frankly speaking this project is quite old (better a L6208 for bipolar motors or other controller), but these chips are so common and so well known that it is not possible to omit them.

Solid State relays are quite popular as modern replacement of traditional, mechanical, relays. Usually are relatively quite expensive units. Now we'll see how to build one of them (for 110 or 220V) using opto-protection input and driven directly by a pin of the parallel port, normally used in a cnc environment.

The project regards the construction of a simple breakout board, partially optoisolated, useful to protect the parallel port of the pc used to control the CNC machine and to simplify the wiring between the port and the controllers of the motor. 

alimentatore CNC

This power supply provides the main supply for the motors and five, separated and stabilized, 5V voltages for the logic of the motor controllers (upto 4) and one for the break out board (or for a fan). It needs of two different voltages: one (9-12V 2A) for the logic and another (18-25V high current) for the motors. 

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