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1:10 Transformer Use with LM2586?

Karl Harrar
Prodigy 85 points
Other Parts Discussed in Thread: LM2586, LM2577

I would like to generate 70-145VDC using the LM2586 adj and a 1:10 transformer. The transformer is a Midcom WE 750032050 that is used for Linear Tech capacitor charge circuits. Has anyone ever used the LM2586 in this manner?

Thanks in advance for any help. Karl

  • 0
    TI__Guru 69475 points

    I do not remember anyone using such a large step-up ratio with this device.  I would be cautious about the parasitics with the transformer.  The LM2577 data sheet

    provides more information about transformers and snubbers than the LM2586 data sheet; so I would look at that.  Also, depending on current and isolation,

    you may be able to use a cap multiplier with the boost to get you HV.

  • 0 in reply to Frank De Stasi
    Prodigy 85 points
    Frank the transformer is used with many of LT's capacitor charge circuits and I have gotten it to run with many different switching controllers. Just really like the LM2586 and want to try it. Will study the 2577 data sheet. Thanks, Karl
  • 0 in reply to Frank De Stasi
    Prodigy 85 points
    Did the calculation and came up with a 220 ohm resistor and .47uF capacitor, will give it a try and let you know how it works. Karl
  • 0 in reply to Frank De Stasi
    Prodigy 85 points

    Frank,

    Can you recommend a TI part that would be better for my application? Do you have a Engineer that has high voltage supply experience? What I really need is a supply:

    Input 12-13.5 VDC

    Output 70-150 VDC variable or fixed feedback

    Output current no more than 2ma

    Output tolerance +/- 5%

    Output noise under 500 milli volts

    The transformer I have is a Midcomm WE part number 750032050 ; it seems very well suited for my application.

    Thanks in advance for any help,

    Karl

  • 0 in reply to Karl Harrar
    TI__Guru 69475 points

    My collegue Alan Martin has a method for getting a high voltage from a boost with a charge pump.  Your application sounds perfect for that.

    You can probably use a smaller power boost than the LM2586 family.  I will pass this to Alan.

  • 0 in reply to Frank De Stasi
    Prodigy 85 points
    Thanks Frank, I look forward to hearing from Alan.

    Karl
  • 0 in reply to Karl Harrar
    TI__Guru 69475 points

    It looks like Alan is out of office; I will ask my colleges is they have the schematic.

  • 0 in reply to Frank De Stasi
    Prodigy 85 points
    Thanks Frank, really appreciate it. Karl
  • 0 in reply to Karl Harrar
    TI__Guru 69475 points

    The attached schematic is what we had in mind; you would only need the positive output.  You can set the boost for a moderately high voltage and then add multipliers to get to your desired output voltage.  The LM2586 might be overkill, however it has a higher switch voltage rating so you would not need as many multiplier stages.

    If you really need the isolation, then you may need to use the fly-back.

    You will need to test this since we did not check this to high voltages.

  • 0 in reply to Frank De Stasi
    Prodigy 85 points

    Thanks Frank I will give it a try. Karl

  • 0 in reply to Frank De Stasi
    Prodigy 85 points
    Frank, Received some LM2586 ADJ parts from Digikey today and thought I would try them with the 1:10 transformer. Works really well! Very happy with the performance and has no problem with 150VDC at several milli amps. I used a simple CRC pi filter and ripple is less than 100mv. Will get a HV inductor and use this with some better caps in a RLR pi filter to get rid of the voltage drop. I will tweak the compensation RC and let you know the final results and schematic used. Karl