Help! DIY 4 amp L297/6203 driver

[tribbles]

I was being facetious about the all-on-one-board

The settings would be global, but it could control all three axes independently (I've done that on my parallel port interface - although the PIC is more of an override for the PC [I've got the capability of having an external keyboard to move the machine around if I'm not anywhere near the PC]).

Digital:

For the non-electrolytic caps (C17, C19), there isn't really too much to worry about (so almost anything). I normally use polyester ones, such as Farnell part 116-6036 (100nF), 116-6039 (220nF).

Eagle PCB 5.6 has these in the "rcl" library -> C-EU -> C-EU050-030X075 (or C-EU050-035X075 for 220nF).

Don't forget you'll need a cap for the supply to IC4 (and also the supply itself).

You haven't got any electrolytic caps on the digital supply side - I'd put one in, around 47µF. I'd normally choose an Aluminium 5mm radial over Tantalum (they can explode quite nastily if you're not careful - mainly if you solder it the wrong way around, but they are known to short internally over time). Farnell part 969-3572.

Eagle PCB 5.6 is rcl -> CPOL_EU -> CPOL_EUE2-5

(Hope you follow the nomenclature)

Resistors (R14, R19, R11, R10, R9) for the digital can be 0.25W quite happily. The smallest size for them to be mounted parallel to the board is rcl -> R-EU_ -> R-EU_0207/7

For the power side:

Non-electrolytics, I'd also use polyester, the 63V ones I mentioned above should be fine, but for the smaller values (15/22nF), then 121-5517 and 121-5518 respectively (they use the 030X075 package).

Electrolytics (only C13 and C11), then you could use Tantalum for them (Tants are good for small space and high capacitance). However, I'd stick with Aluminium. Farnell 969-3793, CPOL-EUE3.5-8.

The 2W resistors I take it are for R1/2/3 and R5/6/7. Not sure if you meant it for R4 and R8 as well, but I'd use them too.

I'm not sure if you could replace R1 and R2 with a single 0.25 ohm resistor (may need to be 4W). Anyway, Farnell only seem to have 0.5ohm 2W resistors in SMT form (they do have a 0.51 resistor, but it's in the US, and you'd need to pay £15.95 for delivery [!]). I'm guessing R-EU_0613/15 package for that one (based on the datasheet for the US item). You could use 4x1ohm resistors (Farnell 156-5440, same package as below).

The 1K resistor (Farnell 156-5434 seems the cheapest in stock), looks like it's R-EU_0411/12.

10R resistor - Farnell 156-5420 (same package as above).

I think you can guess where I get most of my components from

Note that the STTA8 diode does not appear to be available from Farnell, but they do offer the STTH8 instead (same current, but slightly lower Vf [I don't think that'll affect it much - they're only to prevent the back-EMF from the motors from damaging the drivers]).

Also note that I'm using an oldish catalogue for the capacitors (the 2W resistors I did use their website though).

Furthermore note that digital and audio analogue is really my realm, so feel free for people to correct my choices.

Have you decided what type of connectors to use? I really like Farnell 963-2735 style connectors for the motors (I'd used them before I saw them on the drivers I got from Zapp). There are bigger ones for more current if you need it.

[Ross77]

Perfect, glad you chose Farnell.

I was hoping to save you the job but it looks like that idea failed. Shall I continue setting the components or will it be easier for you to choose sizes and orientation whilst laying out the pcb?

I've have a look at some similar designs and they use the larger 100v 7.5mm caps for the output bootstrapping etc. seen reasonable or over kill?

I already have the STTA8's that i can steal from the old board. :whistling: That pin spacing will still be ok if i need to replace them the traditional round diodes.

Thanks again

[irving2008]

I like Phoenix connectors, Farnell part 304-1359. They are cheap and robust (41p for a 2 way, 83p for a 4way)

[tribbles]

I like Phoenix connectors, Farnell part 304-1359. They are cheap and robust (41p for a 2 way, 83p for a 4way)

Yes, I used them for a bit (and even have some spare in both 3.81 and 5.08mm spacing [albeit 6 and 8-way]), however, I prefer the other ones because you can easily unplug them for replacement or testing.

I initially used the Phoenix ones on a steering control circuit for a crop sprayer, but the boards kept on getting water on them, causing problems (the board has now been moved), and the guy who was fitting them was getting a bit annoyed at having to unscrew them, replace the board, and remember which way around the cables needed to go.

Phoenix do make the same style as the one I indicated, but they're more expensive (the two do seem to mate though).

[Ross77]

Ok I'll see what the smallest 100v caps are. The only bit I'm stuck with is the high power resistors. The Original dosnt show a rating and the similar Burger design shows the bootstraps as 2 watt and the sense res as 5 watt! dose this seem right?

The other problem is that although the original board used this configuration the motors are only 2 amp per phase so I will need to lower these values to set a temporary 2 amp max current. This shouldnt affect the pcb layout tho. maybe just use a large res mounted vertically?

[irving2008]

Ok I'll see what the smallest 100v caps are. The only bit I'm stuck with is the high power resistors. The Original dosnt show a rating and the similar Burger design shows the bootstraps as 2 watt and the sense res as 5 watt! dose this seem right?

The other problem is that although the original board used this configuration the motors are only 2 amp per phase so I will need to lower these values to set a temporary 2 amp max current. This shouldnt affect the pcb layout tho. maybe just use a large res mounted vertically?

Vref = 0.5v, phase current = 4A therefore sense resistor is 0.5/4 = 0.125ohm and dissipates 0.5 * 4 W = 2W so need to be 5W rated.

Why would you need to reduce them for 2A, just turn down Vref to 0.25V. I would recommend a 10 turn pot for the Vref trimmer, makes it so much easier to set.

What have you planned for heatsinking the 6203s?

From the datasheet, at 4A you are going to dissipate between 10 and 15W. Max junction temp is 150, max case temp 90 so for an ambient of 25degC you'll need better than (90-25)/15 = 4degC/W heatsink per 6203 - I'd go for ~3degC/W. thats going to need a finned heatsink around 60mm x 100mm each chip...

[Ross77]

Vref = 0.5v, phase current = 4A therefore sense resistor is 0.5/4 = 0.125ohm and dissipates 0.5 * 4 W = 2W so need to be 5W rated.

If it only = 2W then why do the res need to be 5W? I thought vref was up to 1v as well? if so then 1/4 = 0.25 hence the two 0.5r, but this would mean max current is 4W? probably got it wrong again :whistling:

Theres not much available in 2 or 5W resistors in that range as they cant be wirewound.......Why is it possible to get a 2W smd res 30p? dosnt make sense.

For the heat sinks I was going to reuse the originals, their about 50mm square and 140mm long with fan at each end. The 6203's mount on both sides with the fins top and bottom.

Does the shunt regulator have to be on each board or could I just put one on the PSU distribution board?