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High-voltage solid-state relay: TIDA-050063: Selecting the inductor

Jeffrey Chung1
Expert 2635 points
Part Number: TIDA-050063
Other Parts Discussed in Thread: TPSI3052, LM25180

Hi Team,

I'd like to ask you about the value for the smallest size inductor. The customer complained that the size of 560uH inductor(L1) is so big that they can't use it on their board. So please let me know the minimum inductance value for the smallest size inductor.

Regards,

  • 0
    TI__Prodigy 120 points

    Hello,

    First of all, it is important to have in mind that the inductors used for this application need to be rated for the highest voltage (i.e. the maximum battery voltage) in the system, plus some buffer to accommodate for voltage spikes. Inductors that have such high voltages like that one used in the reference design (800V battery voltage; 1kVrms inductor rating) are difficult to come by.

    Having said that, the inductor value depends on a number of factors, including the desired constant charge current and the maximum battery voltage, as well as the desired switching frequency. Can some more system/application information be provided, such as the Vin Max. and desired charge current so that I can run some calculations and provide a better response?

    Thank you.

  • 0 in reply to Hrag Kasparian
    Expert 2635 points

    Hi Hrag,

    Thanks for your kind response. Let me check with the customer about their system information and let you know that.

    Regards,

  • 0 in reply to Hrag Kasparian
    Expert 2635 points

    Hi Hrag,

    As I checked with the customer, the system information is as follows.

    - System voltage : 400V

    - DC link capacitor : 1.5mF

    - Precharge time : 200ms

    Also, please let me know the maximum switching frequency for the smallest size inductor.

    Regards,

  • +1 in reply to Jeffrey Chung1
    TI__Prodigy 120 points

    Hello Jeffrey,

    Thank you for the design specs.  So, in order to charge the 1.5mF capacitance up to 400V (from a fully discharged state) within 200ms, a 3A constant (or average) current is needed.  If using the TPSI3052, the maximum Fsw will be limited to about 60kHz.  Under these conditions a 330uH inductance can be used, (rated for a saturation current of 6A or greater).  Again, the inductor needs to be rated for greater than 400V.

    If an even lower inductance is desired, then a different isolated bias supply needs to be considered, in place of the TPSI3052, in order to provide a greater FET drive current.  This is again due to the fact that using a lower inductance will lead to a higher switching frequency.  The higher switching frequency will, in turn, lead to a higher gate drive current (i.e. isolated bias supply current).  Maybe an isolated flyback bias supply using the LM25180 PSR Flyback IC can be used.  However, with the increased switching frequency the FET will exhibit higher switching/transitional losses, which need to be accounted for.

    Regarding the inductor selection, if you (or the customer) provide me with some inductor series with voltage ratings of >400V, then I can see which would be a good option to use for this application.  In any case, the inductor saturation current needs to be >6A.

    Regards,

    Hrag

  • 0 in reply to Hrag Kasparian
    Expert 2635 points

    Hi Hrag,

    Thanks for your kind response. Let me check with the customer and let you know if resolved it.

    Regards,