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WEBENCH® Tools: LLC ACDC Converter Power Management Question combining Isolated outputs for a high voltage amplifier circuit

Intellectual 310 points

Replies: 8

Views: 58

Tool/software: WEBENCH® Design Tools

General Question about  LLC AC/DC

can I combine the 2 outputs to get a negative and a positive voltage from the LLC Isolated Output? Vo2 and Vo3, do I have to change the direction of a Diode in doing so?

Bastiaan

  • Hi Bastiaan,

    If you only need two outputs (one positive, the other negative), you should be able to accomplish this with four windings on the secondary, two for each output. The rectifying diodes would need to be flipped and any polarized caps would need to be flipped as well.

    Best Regards,

    Ben Lough

  • In reply to Benjamin Lough:

    Thanks Ben,

    It’s that straight forward? I thought flipping the diode and capacitor had affect the input circuitry in some sort of way?

    Something els, imagine the VO1 is a unregulated 5V, but I get 7.1V however if seen from a no load point of view giving me at 7.1V 250mA., if I pull out all current from this circuit, where does the voltage go to?

    Best

    And thanks allready.

    Bastiaan

  • In reply to Bastiaan Pierik75:

    Hi Bastiaan,

    Since this is an isolated supply, the primary should not care if the output is negative or positive, as long as the correct polarity is maintained for the rectifiers, caps, etc on the secondary. Let me point you to PMP40379. This is a power supply reference design with bipolar outputs for an audio amplifier. Full bridge rectification was used on the secondary to reduce the number of windings needed for each output from 2 each to 1 each:http://www.ti.com/tool/PMP40379

    I don't quite understand your second question. Could you provide more detail?

    Best Regards,

    Ben Lough

  • In reply to Benjamin Lough:

    I am trying to understand if, the program poweresim, means with unregulated output on VO1, it gives me in stead of the 5V I wanted a 7.1V output. I would like to use this for the microprocessor, and I don’t know if poses a problem. if I go over the 0.25A what will happen with the 5V or 7.1V ? Does it break down?

    It’s fine if I add a7805 to transform it to 5V

    thanks for the Pdf I’ll have look at it during the weekend.

    Best

    Bastiaan

    Bastiaan

  • In reply to Bastiaan Pierik75:

    Hi Bastiaan,

    How close you will get the unregulated output to the desired output voltage will depend quite a bit on how well the coupling between the transformer windings of your regulated output and unregulated output. As you increase the load on the unregulated output, I would expect the unregulated output voltage to droop as the load increases.

    I would imagine your processor has a set range of acceptable input voltage. I think using a step down regulator from the unregulated output winding is a good idea to avoid the voltage from shooting too high and damaging the processor.

    Best Regards,

    Ben Lough

  • In reply to Benjamin Lough:

    Thanks Ben so this counts for the circuit that if no load is applied, I get 7.1V, and will droop if load ’applied, does this count if the load goes over a certain amount or, at the moment if the load increases in the first 10mA?

    Curious about this.

    I have seen the paper to

    because if I change the design, by adding a graetz circuit  After the secondary winding I’ll level up the voltage by 2sqrt2.

    That would impose some changes in the equations. And circuitry before the transformer and filter circuit.

    Is there a good guideline cookbook to this?

    And how far is webench in designing such topologies?

    Have a nice Sunday!

    Bastiaan

  • In reply to Bastiaan Pierik75:

    Found a good cookbook/ rule book

    Some basic rules and the point with the diode rectifier/graetz bridge:)

    Do you have any books to recommend?

    best Bastiaan.

    Bastiaan

  • In reply to Bastiaan Pierik75:

    Hi Bastiaan,

    I think this document may also be helpful to you:https://powersimtech.com/drive/uploads/2018/04/Designing-LLC-resonant-converter-TI-slup263.pdf

    Best Regards,

    Ben Lough

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