Power Distribution MUX Using 40-500

    The 40-500 can be used as a MUX for distributing power supplies to many pins of a test system.

    Use of low power relays (reeds or EMR's) to distribute power to a test system where the signal needs to be hot switched can be problematic as power supplies have decoupling capacitors in the load and the source (the power supply) includes an output capacitor that is not subject to current limiting by the power supply. Even the current limit on a power supply relies on a feedback system, so a current limit does not immediately operate when a load is hot switched. All this can shorten the life of relays, or indeed cause them to fail very quickly. For more information see Hot switching relays

    Most switching systems are designed so that the PCB tracks match the rating of the relays and that can create additional problems. If a switching system is to distribute say 100mA to 50 test points then the power supply connection would have to support 5A. That would often infer a 5A switching system design and larger relays.

    However some designs do have higher track ratings than the relays used, and 40-500 (and 40-501) is an example.

    Using 40-500 as a Power Distribution MUX

    Suppose the application requires the distribution of a power rail to 64 test points each of which can take up to 100mA and it has to be hot switched to reduce test system speed. The power supply needs to provide up to 5A.

    The 40-500 is a 64x4 solid state matrix, the solid state switches are well suited to hot switching into capacitive loads without a lifetime degradation and their speed of operation makes them a good choice in applications where speed of test is important. The 40-500 can be used as a power distribution MUX as shown.


    Diagram of the 40-500 MUX used as a power distributor

    Each Y bus of the 40-500 is rated at 3A, it can easily support 16 connections at the same time each carrying 100mA. So by connecting the power source to Y1, Y2, Y3 and Y4 and then allocating 16 X connections to be used on each Y. The required 1.6A on Y is easily met by the 40-500. Each crosspoint switch can support 0.5A continuously so easily meets the 100mA requirement.

    The drawing shows Y1 connecting to X1 to X16, Y2 connecting to X17 to X32, Y3 connecting to X33 to X48 and Y4 connecting to X49 to X64. The grey tracks and crosspoints are not used, only the red tracks and crosspoints are used.

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