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Answered

PWM as control signal

Ed Schippers 3 years ago updated by Gustav Widén (System support) 4 months ago 3

We want to use Spal brush-less fans, these fans have integrated electronics that control the fan speed. the speed can be controlled by a PWM signal mr 0 to 100% frequency 50 to 200Hz.

Is it possible to use the PWM output of the Iqan system to control this?


Regards, Ed

Answered

You could use the PWM output on e.g. an XA2 or XC10 to do this, but there are a few limitations to think of.


The most important is the off-state leakage current on the highside driver. This is just as relevant for the case when one wants to use DOUT as a signal to another controller. If you do not pull the output to ground, you will see a voltage on the output pin that is close to +BAT level. The other will have some voltage threshold that you must be sure to be able to come below.

It is very probable that the PWM input on the other device have a pull-down resistor in the kOhm range. Then you will need to add an external pull-down resistor to load the signal. Which is tricky because this low resistance component will also have to cope with the power during the on-phase.


Another limitation you need to consider is the PWM out range. As the IQAN PWM outputs are primarily intended to drive valves, none of the outputs go all the way to 100% MR.


For modules that has undercurrent detection (like XC10), you might need to switch this off, depending on how much you load the output.

Interesting to confirm if the base frequency of the MC41 or other MC4x module.

My customer tried to use them as PWM driver for batteries charger in EV vehicle and got lots of issue to obtain a constant base frequency (not the ratio of the PWM itself). As they need to use a 128Hz value for their system, they had to go with trialand error to find the correct PWM frequency value to be get near the 128Hz. The final value was 120Hz to get 127.5hz output. They got variation like +/- 10 to 15Hz against the requested value.

Their is any know issue or information to explain with they have so large error on this ?

As they have to create a load on the output, can it be not enough? They don't have error, but this can create issue.

Regards,

David

The module cannot generate every frequency, it is limited to a fixed set of frequencies. 

When typing in 120 Hz as PWM frequency on an MC4x, the expected result is not actually 120 Hz, you should be seeing it clamped to 125 Hz. 


If you were to type in 126 Hz, then the resulting frequency would be 166 Hz.