Help! DIY 4 amp L297/6203 driver

[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?

[irving2008]

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?

You are right, Vref for the L297 is 1v - I was confusing it with the TBA6560 chip on the other thread... so the sense resistor should be 1v/4A = 0.25ohm non-wirewound, rated at 1v x 4A = 4W you would derate by 25% - 50% so really you need something rated at 5W - 8W

Look at the datasheet for this 0.5ohm SMD resistor from Farnell (you'd need 2 in parallel to give 0.25ohm/4W). At its rated dissipation it needs, and I quote "2 Watts with total solder pad and trace size of 300 mm2" - I doubt you'll be close to that amount of copper, and even if you were the temp rise is 90degC above ambient... thats 105degC+ - ouch!

A better product is this nickel chrome metal resistor from Vishay, also from Farnell. This is rated at 5W and seemingly doesnt need a heatsink, but will hit 120degC at rated load so some airflow would help.