From: "Frank Bemelman"
Subject: Re: L297/L298 Bipolar chopper stepper drive problem
Date: Mon, 28 Oct 2002 22:26:58 +0100
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Organization: EuroNet Internet
NNTP-Posting-Date: 28 Oct 2002 20:27:02 GMT
"MarkP" schreef in bericht
> We are using the MAE stepper motor( 6 lead HY200-1713-040-B6 0.4A/phase,
> 15.6R phase resistance) for development, previously we were using a
> driver, namely a UCN5804B device from Allegro, but with the documented
> of power efficiency, we decided to develop a bipolar drive. I used the
> L297/L298 combination, as I felt this would give me a better grounding in
> how the bipolar chopper functioned, layout requirements, power dissipation
> that sort of thing.
L297/L298 is a good old stepperdriver, but you really should have a look at
the L6208, also from SGS/thomson. Your current requirements seem low
enough to use the SO24 package. 15.6R, is that 31.2R for the bipolar
> The issue...when the motor is in a static position, a holding torque
> applied, the motor is starting to overheat, when the motor is moving
> (typically at 600 steps/second) the motor behaves as it should and does
> exhibit any overheating. How can I prevent the overheating in the static
> position, is there something I'm missing (likely)?
If your motor is running too hot when stopped, your only option is
to lower the current. In half-step mode, try stop the motor in such a
position that only one winding is energized (if possible).
> We are using a 15V power supply for the motor. The controller from start
> always enabled, we're in half step mode using Enable Chopping (not phase
> chopping). For the current sense, a pair of 0R5 resistors are employed
> a reference voltage for the comparator set at >0.2V (max phase current =
> 0.4A). The chopping frequency is about 20KHz.
> At the static position, if I decrease the Vref to near or lower than the
> sensed voltage (current), then the Vref and current sense inputs become
> 'noisy' and although the motor maintains a holding torque, albeit with
> vibration, the phases are now being turned on and off. The datasheets talk
> about chopper stability and that if spikes on the sensing inputs exceed
> Vref, then the comparator can be fooled into resetting the flip-flop; it
> describes including an RC on the sense input to the comparator or to use
> inherent set dominance of the flip-flop to mask out the spike.
Perhaps you should increase the current-measurement resistors, so that you
can use a higher vref while running the motor, and still have a nice vref
when you lower it, once the motor is stopped. That should give you less
noise problems, but a good solid PCB layout is also highly recommended.
> I've tried increasing the chopper frequency and including an RC at the
> inputs to the L297 from the sense resistors, without any noticeable
> I hope someone can help.
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