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TIDA-00289: Detection of Plunger Movement in DC Solenoids

Sjamikapoor Gangadin
Prodigy 30 points
Part Number: TIDA-00289
Other Parts Discussed in Thread: TIDA-00284

Hi,

I need to design a plunger movement detection for elevator brakes in which the DC voltage used to excite the coil is always unfiltered DC and comes directly from a bridge rectifier. In this reference design the used voltage is filtered, so the current trace is smooth, while this is not the case with unfiltered DC.

Do you have any suggestions how I can solve this in this circuit?

Thank you in advance.

Sjamie

  • 0
    TI__Intellectual 1260 points

    Hi Sjamie,

    Have you tried to characterise the solenoid with the unfiltered DC supply. The waveform would have helped to analyse better.

    When the solenoid is activated, the region of interest is the initial transition of current waveform which could be spanning a couple of tens of millisecond. During this phase there could two ripple content in current, one due to the unfiltered DC ripple and the second during the plunger movement. I guess the dip in current during plunger movement will be more deeper (for a couple of millisecond), compared to the current variation due to DC voltage ripple (which spans for more time, ex: 10ms). So I think we will be able to differentiate the scenarios. You can also provide some capacitance at the DC bus to bring some filtering on the DC voltage. We have another design TIDA-00284, which show the current dip with a rectified voltage from 230V AC (having voltage ripple), refer figure 29 in https://www.ti.com/lit/ug/tidu584a/tidu584a.pdf

    Thanks & Regards,

    Manu

  • 0 in reply to Manu Balakrishnan
    Prodigy 30 points

    Hi Manu,

    Thank you very much for your prompt reply.

    I have not characterised this coil yet, because this was recently asked to me and then I saw this artikel which triggered my interrest. Even though you helped a lot with this new document and your input, so I will have some help with that during my development.

    Thank you again and have a nice weekend!

    Regards,

    Sjamie.