Electronic – Options for Universal Input Power Supply

power supplyswitch-mode-power-supply

I develop products that are sold all over the world. The line voltage may be one of (100, 120, 220, 240). I am currently considering options for handling this requirement. We typically have a 5V rail that needs a couple amps, and 15V rails that need under an amp. Perhaps another tap with a higher voltage.

Options:

  1. Transformer and Linear Regulators: This is what we presently do. We have a power entry module like this where the user can install the fuse differently to select the correct voltage.

    • Pros: Clean Supply (we measure extremely small signals with these devices), Simple to achieve Galvanic isolation with multiple secondaries, With undervoltage and overvoltage accounted for, the device is not damaged even if the fuse is installed incorrectly.
    • Cons: Bulky Transformer, We have to change the fuse drawer based on destination address which adds a manufacturing step. Also, we occasionally sell to OEMs who then resell their system to unknown addresses.

  2. Switched Mode Power Supply:

    • Pros: Can handle variable input voltage.
    • Cons: The switching introduces noise which will impact the performance of some of our products.

I am not asking for a decision from the above options, but rather wondering if there are any other options to put on the list. What do you guys do?

Best Answer

You really have the only two answers there are: Linear or SMPS. There are some things you can consider though to make you designs more robust regardless of which you choose.

Linear: Designing a Transformer that can take each of those input voltages and output the correct secondary would not be too difficult. You can double wind the input transformer and have it select between 100-120Vrms and 220-240Vrms. Then with the linear regulators you simply allow them to regulate when the lowest rms voltage is present and burn more power then the highest rms voltage is present.

schematic

simulate this circuit – Schematic created using CircuitLab

SMPS: These are much harder to design. There are more regulations regarding their standards internationally. They are lighter weight. If you're worried about sensitive electronics, Use a constant switching frequency and then make a notch filter on the output specifically targeting that frequency.

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