Open Source Boards Available, Stepper Drivers and Break Out Boards

[pminmo]

Originally Posted by Urbania 1. In the documentation for the L297-8 drivers PMinMO mentions the fact that we can use LM138/338's instead of the LM317 voltage regulators. My question is, is the LM338K a drop-in replacement for the LM317? (with obvious regard for the BCE configuration, and the maximum current rating of the L298's ) Regards, Wayne

Where do I say you can sub a LM138..LM338?

As far as I know the LM138..LM338 are only available in TO-3 packages. The pcb for the L297-8, the LM317 is a TO-220. Two entirely different mechanical packages.

[Urbania]

Originally Posted by pminmo Where do I say you can sub a LM138..LM338? As far as I know the LM138..LM338 are only available in TO-3 packages. The pcb for the L297-8, the LM317 is a TO-220. Two entirely different mechanical packages.

PMinMO, my apologies. I was reading through various PDF's covering open source boards today, and obviously I mistook the PDF as being one of yours. I'm trying to find the one I read where it stated that if our amperage requirements are higher than 2.5A or so we should consider going the route of LM150/350 or LM138/338, but for the life of me I can't find it now. I know I read it today while browsing through the PDF's but I can't remember where! I was using my work PC at the time and i'm using my home PC now so I can't even check my IE history.

Anyhow, I too realise that the TO-3 package is vastly different to the TO-220 package, but apart from the obvious issues mounting a TO-3 with heatsink to the PCB, it is still an easy task to substitute the LM338K if it will work in the circuit.

I'll try and find the relevant PDF when i'm at work again in the morning.

Wayne

EDIT: Oh bugger! I remembered where I read it, and it wasn't even a relevant PDF. It was in the datasheet from National Semiconductor! Clearly i'm getting old! Quoted below.

For applications requiring greater output current, see LM150 series (3A) and LM138 series (5A) data sheets. For the negative complement, see LM137 series data sheet.

FURTHER EDIT: In support of my other question, here is another quote regarding the fact that the max voltage handling capabilities of the LM317 refer to the differential between the input and output voltages, and not the maximum voltage above ground that the regulator can handle -

Besides replacing fixed regulators, the LM117 is useful in a wide variety of other applications. Since the regulator is “floating” and sees only the input-to-output differential voltage, supplies of several hundred volts can be regulated as long as the maximum input to output differential is not exceeded, i.e., avoid short-circuiting the output.

[pminmo]

Both the 317 and 338 are floating regulators, so max input to them is the regulated output voltage plus the differential max. So for a LM317 that is configured as a 5V regulator, 45V is the max input voltage. (40V max differential). The 338 has a 35V max differential verses the 40V of the 317. Computing resistors is the same, except Iadj is slightly different.

BTW you don't need to regulate the voltage for the motors, if your thinking motor current comes into play.

[Urbania]

Thanks for the feedback PMinMO. I was thinking of using an LM338K instread of the LM317 to reduce the workload on the regulator at higher currents. By that I mean that if you run a device rated at 3A at 3A you are driving it hard and will have issues like a high average working temperature and shortened lifespan, whereas if you run a device rated at 5A at 3A you are more or less in the mid-band of the device's capabilities which should reduce the impact of temperature and lifespan.

Over and above that, I would like to run my boards at 3A if possible to cater for a few higher torque motors I have scrounged.

Wayne

[pminmo]

Again, the regulators in the circuit, as designed, DON'T play in the motor current......... You don't need a 5A regulator for a less than a 100ma. If you look at what the LM317 runs, it's the 5V on the board. The incomming unregulated VDC (18V or more) is used for the H bridge of the motor in the L298.

If your thinking of regulating the supply voltage to the motors, don't, it's a waste and more times than not reduces performance.

[Urbania]

Originally Posted by pminmo If you look at what the LM317 runs, it's the 5V on the board. The incomming unregulated VDC (18V or more) is used for the H bridge of the motor in the L298.

Thanks again for the feedback PMinMO. Clearly I am not understanding the circuit well at all. I'll go back and take another look at it and figure it out.

Wayne

[dongduong]

Help me! i want to try with Tach's 3axis board(driver and choper) but i have problem!!!
can i change irlz44 as irf540? and i can't buy IRF9540 in my place,help me to find out IC same as to change it.
Thanks so much!!!!