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[on:]

Hi!

I'm designing a stepper driver board and want to use the stepper library, which means I have a A+/- and B+/- output (4 pins), and not the input pins the L297 would use.
I want a current limiting circuit, and so I choose to use the L6506 and the L298. But I have some questions. First, the motor has 2 phases, is bipolar, 1A per phase, 8.6V, phase resistance 8.6ohm and a phase inductance of 18mH.

I found this citcuit for those chips:

Here are the datasheets:
http://www.st.com/internet/com/TECHNICAL_RESOURCES/TECHNICAL_LITERATURE/DATASHEET/CD00000097.pdf
http://www.sparkfun.com/datasheets/Robotics/L298_H_Bridge.pdf

The motor will be powered with 12V.

So here is the bunch of questions I have

1. There are two resistors which are called Rsense. They can be calculated using the formula Ipeak=Vref/Rsense. But what is Ipeak? In my case 1 or 2A? I think with the Ipeak = 2A, the resistor value would be 6ohms. And what is Vref? Does this have something to do with the two ref pins? I would be glad if someone could explain this part of the circuit to me.

2. There is a resistor between pins 16, 17 and GND. What size should it be?

3. There are 2 enable inputs on the L298. Do I understand this correct, I just have to tie them to 5V if I want the chip to work?

4. The L6506 has a enable input too. Same here?

5. Do i have to look for something special for the diodes? Or will 1N4004 do?

6. Watt rating of the resistors: the 22K wont have a large wattage drop, I guess 1/4W will do? So for the mysterious resistor without a name? The Rsense resistors will have a huge rating, I'll look for 30W resistors, right?

Thank you very much!

[Reply #1 on:]

Some more information I found in the datasheet of the L6506:

When the current in the load winding reaches the programmed peak value, the voltage across the sense resistor (Rsense) is equal to Vref and the corresponding comparator resets its flip-flop interrupting the drive current until the next oscillator pulse occurs. The peak current in each winding is programmed by selecting the value of the sense resistor and Vref.

This would mean I calculate with 1A. I guess Vref is the voltage applied on the two Ref pins, which is 5V in this case. This again would mean 1A = 5V/Rsense, which would be 5Ohms.

If anyone could help me, I would be really glad and could continue building my project...

[Reply #2 on:]

I found in the maximum table in the datasheet, that Vref is maximal 3V. This again would leave me with 3Ohms. And this would lead to a power dissipation of 48W on the Rsense! What did I understand wrong?

[Reply #3 on:]

The motor windings will take 1A at 8.6V, the supply is 12V, the L298 will drop 3V or so at 1A, so the motor will only see 9V, no need for the L6506 at all I think (unless you want to run at lower currents)...

It the power supply was 24V or 36V or similar then this circuit would be very suitable.

[Reply #4 on:]

The motor windings will take 1A at 8.6V, the supply is 12V, the L298 will drop 3V or so at 1A, so the motor will only see 9V, no need for the L6506 at all I think (unless you want to run at lower currents)...

Actually I want to control the current, not the voltage. Or why do you say the circuit is "useless" if the voltage is so low? Sorry, I don't really understand that, but I'm really open to ideas.

[Reply #5 on:]

Here is a link to a similar chopper circuit that has links to the schmatic and the kit manual.  It  might give you some ideas.
http://www.circuitspecialists.com/the-stepper-motor-chopper-driver.html

Bob