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Bulk power supply LY6806 based

Discussion in 'Power Electronics' started by vidalv, Jul 3, 2021.

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  1. vidalv

    vidalv

    2
    0
    Jul 3, 2021
    Hello all, I am looking for a schematic or a data-sheet for the LY6806 circuit.

    On the website http://www.stglsemi.com (which seems abandoned since 2014) nothing available.

    This circuit is used in a variable 3V-24V 3A cheap power supply.

    Thank you for any information.
    AdaptateurAC-DC.JPG Alim24.jpg Alim25.jpg
     
  2. PETERDECO

    PETERDECO

    166
    40
    Dec 19, 2019
  3. vidalv

    vidalv

    2
    0
    Jul 3, 2021
    The power supply is working. My problem is to use under 3.65V (to supply a 3.3V devices) this voltage is a little bit high. Unfortunately no chance to reduce it easily. So, finding nothing on the SMPS LY6806 circuit, I looked at the secondary of the circuit, here is the schematic:
    Output.JPG
    The heart of the circuit is a TL431A, this circuit, from several manufacturers, like T.I,is an "adjustable precision shunt regulators".
    It has a reference voltage on the Pin1 = 2.50V.
    As a reminder, my concern is to go down the output voltage below the 3.65V currently available.
    Given the concept of the circuit I guess we must not be able to go down below the ref of the TL431?
    A voltage min at 3V would suit me, for the max it is not too important if I can get 15V or more it will go.

    So I replaced R10 from 39k by a 50K Pot. and R11=4K7 with another 5K pot.
    With the original adjustment for R10 and R11 I observe a variation of the value of the output voltage from 3.65V to 24.1V.

    If I modify R11 (R10 set to Typ.) Only the value of the max voltage changes, with 4K7 I get 23.1V, with 4K it rises to 26.3V, but in the 2 cases the min remains at 3.65V !!!

    In the other case, if I fix R11 and modifies R10 this is the value of the max which decreases, the min remaining at 3.65V

    I do not have too much idea about the operation of the circuit?

    If there are experts? Some explanations could help me ....

    Thank you.
     
  4. PETERDECO

    PETERDECO

    166
    40
    Dec 19, 2019
    Personally, before I spent the effort altering circuitry, I would just use a diode in series with the output. It will drop about 0.6V so you would need to set the PS to about 3.9V to get 3.3V out. I would also add an electrolytic after the diode to keep the impedance low.
     
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