[Solved] Protecting MD Chips & Arduino from Transient Voltages?

[Redcap]

OK, so I've done a little more research into what I want to do, but need some help, as per this posts title.

I wish to use the SN754410 Motor Driver chip in this type of setup.

I know that motors produce transient voltages when their electric field collapses, which can damage parts. Because I haven't had my Arduino for very long & am still rather new to electronics, (plus tight budget), I'm (more than) a little paranoid about frying it.

The SN754410 has internal Clamping Diodes, but the data sheet shows a schematic with stepper motors using external diodes [fig 3]. (Just for clarity, I wish to use hobby DC motors in the setup)

Is there anyway I can calculate if these internal diodes will be enough to stop my little Ardy and the SN754410 itself from being fried? (or how high transient kickback voltages could potentially be?)

Much thanks in advance,
Redcap

[Soeren]

Hi,

The SN754410 has internal Clamping Diodes,

For ESD protection, yes.

Is there anyway I can calculate if these internal diodes will be enough to stop my little Ardy and the SN754410 itself from being fried? (or how high transient kickback voltages could potentially be?)

You have no data (neither on the diodes, nor the motors I guess) to calculate from and it would probably be a bit much having to calculate inductive kicks even if you had them
Get some fast diodes and be on the safe side. The ESD protection diodes may do it, but you have no way of knowing and adding some fast recovery diodes is a fairly cheap way of being sure.

[Redcap]

Much thanks, Soeren
-I'm yet to select the two DC motors (had two, but found they were different RPM's )

Get some fast diodes and be on the safe side. The ESD protection diodes may do it, but you have no way of knowing and adding some fast recovery diodes is a fairly cheap way of being sure.

Sounds like it may be the easiest (and smartest) solution, yes
And verified. (as below)

(http://www.ladyada.net/make/mshield/use.html)
On using the SN754410: Some people use the SN754410 motor driver chip because it is pin-compatible, has output diodes and can provide 1A per motor, 2A peak. After careful reading of the datasheet and discussion with TI tech support and power engineers it appears that the output diodes were designed for ESD protection only and that using them as kickback-protection is a hack and not guaranteed for performance.

Now... I'm not sure what specifications I require the diodes to have.
Is this based on how much Amperage the motor/s need only?
I know the motors I choose will draw less than 1A (each).
(the MD chip I'm planning to use has 1-A Output-Current Capability Per Driver)


If it's amperage only, I'm assuming something like the UF4007 or the FR157 suffice.
(I can get the FR157's cheaper.)


Any help or nudge in the right direction would be greatly appreciated
Red

[Soeren]

Hi,

Now... I'm not sure what specifications I require the diodes to have.
Is this based on how much Amperage the motor/s need only?
[...]
If it's amperage only, I'm assuming something like the UF4007 or the FR157 suffice.
(I can get the FR157's cheaper.)

Besides the current - not the forward current, but the reverse or kick back - it's about speed and the FR157 is a bit slow compared to other fast recovery diodes.
The faster it reacts, the lower the kick back voltage gets (as it's quenched before reaching high amplitudes), a slow 1N4007 won't react until the voltage gets really high.

If you go for the UF400x (don't confuse this with a common 1N4007, which is magnitudes slower), the fastest are UF4001 to UF4004. The UF4005 to UF4007 are 50% slower (but still fine for your app).

Personally, I use the BY127 for much of such jobs, as its recovery time is 25ns max. (500ns max for the FR157)

[Redcap]

Ahh, thank you very much for clearing this up for me!
Cheers