Pololu A4938 - with or without voltage regulators??

Hello all

Following my failed attempt at replacing the stepper driver chip on my burnt out G3 stepper board I am once again seriously considering using a pololu stepper driver to replace the burnt out stepper driver.

Browsing for a reasonable priced supplier I stumbled upon 2 versions of the driver. The standard version and the version with voltage regulators. The latter is almost 6 quid more expensive and I was wondering if it was worth it. It seems to me the only value in the voltage regulators is that one need only provide a single voltage rather than 2 separate voltages (one for logic and 1 for the motor). Could anyone clarify this point? I have an ATX power supply 5v and 12v is not a problem.

Finally, the standard version requires 'appropriate decoupling capacitors close to the board'. What are appropriate decoupling capacitors and why should they be close to the board. And how close is close?

Thanks

Best thing would be to look at the Pololu electronics page, as it shows the various implementations and so on.

BTW: Pololu are having their Black Friday sale during the next week, so you can pick up a single Pololu for $7.75, which is probably even cheaper than you thought. Check the thread in this section of the forum for details.

Hi Cefair

I am afraid I am in the UK so the sale will not work for me - shipping costs and customs duties etc...

Ahh fair enough. Keep forgetting Techbots are in the UK.

Anyway, 100uF electros across the motor side of each board seems to be be pretty standard, and a 100nF cap across any supply input seem quite common.

Just make sure to use components rated a bit higher voltage than your supply. That way, if something goes wrong, hopefully you can recover some bits, and also not end up with exploded caps everywhere.

We are running standard Pololus on ATX power supplies. They seem to be working fine, straight up on both voltages (no decoupler's). The oldest one has well over 500 Hrs of print time on it. I'd say: Save yourself the money, buy the standard version. Word of caution though: Keep It Cool! Heat sink and fan. Better safe than sorry.

I got the standard ones, but they're all on the same board and only a few cm away from the 7805. decoupling is very important around high frequency, high current PWM- you can't have too many 100nF caps on the supply rail! a few 1nF for the really high frequencies is good too. Probably a good idea to keep the 5v ground and 12v ground separate except for one point- that 12v ground will be carrying lots of noise, don't want it transferring to your signal inputs!

having said that, I have a tendency to over-engineer things a little.

---

-----------------------------------------------
Wooden Mendel
Teacup Firmware

The high frequency decoupling caps are included on the carrier PCB, close to the chip where they need to be, so you only need to add bulk decoupling, which doesn't need to be so close.

I used 47uF on the 12V line and 10 uF on the 5V line on veroboard about 20mm from the carrier. If your connections to the power supply are short and thick you will get away without them, as Bruce seems to, but as TH says better to over engineer as the faults you get with inadequate decoupling can be very confusing.

---

[www.hydraraptor.blogspot.com]