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Polarity switch for a DC-DC converter

Michael Levin45
Prodigy 170 points

Hello support team,

I have an isolated DC-DC converter with output voltage of up to 40V, and I would like to connect it to the output terminals of the power supply that I'm building.

One of these terminals is grounded, while the other is not. So there are two possible configurations with either positive or negative terminal grounded. I would like to implement a software control of the output polarity, so I need an electronic switch. The straightforward solution would be to make a full bridge using four FETs, and provide gate drivers for them, which is a long story. So my questions are:

1. Can you recommend a specific IC that includes all this circuitry (full bridge + control)? The maximal load voltage is above 40V, the ON-state resistance should be a few milliohms.

2. If there's nothing like this - can you recommend a gate driver IC (preferably isolating) that would control a full bridge built using four discrete N-channel FETs?

In both cases, switching time is not critical.

Thanks in advance,

MIchael

  • 0
    TI__Intellectual 2061 points

    Hello Michael,

    Yes, as you say there will be many solutions. Could you please advise:

    1. what the current will be loaded on the 40V power supply?

    2. Do you really need 40V? or 25V is OK?

    Thanks.

    Wei

  • 0 in reply to Wei Zhang
    Prodigy 170 points
    Hello Wei,

    1. With 40 V, the current will be about 1 A maximum. But with 3 V (it is a buck converter, and I can set the output voltage between 1 and 40 V) the current can reach 10 A. That is why I haven't specified the current, and specified the ON-state resistance instead (a few milliohms).

    2. Yes, I do need 40 V for the present design.

    Thanks in advance,
    MIchael
  • 0 in reply to Michael Levin45
    TI__Intellectual 2061 points

    Hello Michael,

    Thanks so much for the information.

    if the polarity doesn't require high speed, a simple relay (elect-magnetic relay) would work? it was simple, however, it has larger quiesient current consumption and the size would be relatively larger than FET solution.

    If you consider FET, you are expecting a full bridge and gate driver and floating power supplies to support the high side driver since the switching frequency is low and you have the possibility to keep the high side switch on.

    Please advise more on your thoughts.

    Wei

  • 0 in reply to Wei Zhang
    Prodigy 170 points
    Hello Wei,

    Electromagnetic relay is not an option of course.

    As for the FETs, I do not have much to add to my initial question. Yes, I'm expecting a full bridge and the gate drivers. I was wondering if you have an integrated solution - either full or partial. If there's no such solution - please don't hesitate to tell me :-)

    Thanks in advance,
    Michael