Help! DIY 4 amp L297/6203 driver

[Ross77]

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

Phew I thought I was going mad. thanks for the smd links but I think I'll stay away from them at the mo. i just couldnt understand how such a small part was so powerful and cheap.....

Looks like digi-key are the best for this project. in fact they are cheaper on a lot of things, I just need to spend £50 for free delivery. Any body need parts? I can get 2watt res for 13p each, if I use 3No. 750 ohm in parralel = 250 ohm at 6 watt correct?

[irving2008]

Phew I thought I was going mad. thanks for the smd links but I think I'll stay away from them at the mo. i just couldnt understand how such a small part was so powerful and cheap.....

Looks like digi-key are the best for this project. in fact they are cheaper on a lot of things, I just need to spend £50 for free delivery. Any body need parts? I can get 2watt res for 13p each, if I use 3No. 750 ohm in parralel = 250 ohm at 6 watt correct?

That is correct...

[tribbles]

Any body need parts?

Let me know how short you are off your £50 - I may have some bits that I can order from Digikey.

[irving2008]

Ditto, i need to order a few small bits, not urgent but if you need a couple of quid extra let me know... stuff i need can be posted to me with a 2nd class stamp...

[Ross77]

Let me know how short you are off your £50 - I may have some bits that I can order from Digikey.

Ditto, i need to order a few small bits, not urgent but if you need a couple of quid extra let me know... stuff i need can be posted to me with a 2nd class stamp...

Sure pm me with what you want. it would be good to help a little, after all the help you guys have given me. Dosnt matter if I go over, just said £50 min.

just about there with with the design. I've had a crack at laying out the pcb but I dont think it will fit on the 100x80 board in eagle, I'm sure you will prove me wrong.....

[Ross77]

Ok so heres the final draft..........

The only thing I cant work out out is what the diodes (D9,D10) for the shunt reg need to be? Any over obvious problems?

Once its all confirmed and if anyone is interested I can post the eagle files.

[irving2008]

Ok so heres the final draft..........

The only thing I cant work out out is what the diodes (D9,D10) for the shunt reg need to be? Any over obvious problems?

Once its all confirmed and if anyone is interested I can post the eagle files.

they are zener diodes. You need a total voltage of Vclamp - 1.4. By using 2 diodes you can get a bit more fine tuning of the voltage, for example a 30v and a 7.5would give a clamp of 30 + 7.5 + 1.4 = 38.9 which would be good for a 36v supply on 40V drivers...