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Boost Convertor using LT3757

Discussion in 'Power Electronics' started by Gokul010, Jul 26, 2021.

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  1. Gokul010

    Gokul010

    4
    0
    Jul 26, 2021
    Hi,

    I am designing a boost convertor using LT3757A for an output of 180V, 100mA from an input of 24V. I have simulated the circuit successfully using LT spice and got the required output. But when testing in the real time I am not getting the required voltage of 180V, whereas only 100V. I could also see that no input current was drawn by the system at the time of tesing.

    Problems encountered during real time testing

    1) Low output Voltage of 100V instead of 180V.

    2) Output is dropped to 30V when a load of 1.8K is connected.

    Components used at the real time testing

    1)Inductor- API Delevan( 4590R-224K) 220uH fixed inductor

    2) Mosfet- (IRLI640GPBF) Vishay Semiconductors 200V VDS, 1V Vth

    3) Diode- (SR320 R0G) 200V Vrrm 3A

    4) Current sense resistor- .09 ohms.

    5) output capacitor (A759KS475M2EAAE496) KEMET 4.7uF.
     

    Attached Files:

  2. Bluejets

    Bluejets

    5,001
    1,050
    Oct 5, 2014
    Spec shows sync pin connected to ground, don't see any on your diagram. (pin 5)
     
  3. Gokul010

    Gokul010

    4
    0
    Jul 26, 2021
    Yeah! but I have connected it, while testing
     
  4. Bluejets

    Bluejets

    5,001
    1,050
    Oct 5, 2014
    Anything else you left out....???
     
  5. WHONOES

    WHONOES

    1,170
    319
    May 20, 2017
    If you are using the values shown on your simulation, then feedback resistors R5 and R6 are incorrect. With the values shown, 220K and 5K the gain of your circuit is 220 / 5 +1 which comes to 45. The reference voltage on the LT3757 is 1.6V. 1.6 x 45 is only 72V. For correct gain to achieve 180V you need a gain factor of 111.(5 (180 / 1.6)-1). I think you should try adjusting the gain setting resistors accordingly and try again.
     
  6. crutschow

    crutschow

    119
    27
    May 7, 2021
    Post your .asc simulation file.
     
  7. Gokul010

    Gokul010

    4
    0
    Jul 26, 2021
    yes, but I have also done it for 550K and 5K but the voltage is not going above 100V, when testing in the real time
     
  8. Gokul010

    Gokul010

    4
    0
    Jul 26, 2021
     

    Attached Files:

  9. Harald Kapp

    Harald Kapp Moderator Moderator

    11,667
    2,700
    Nov 17, 2011
    My guess is that the MOSFET is not suitable. The BSP89 is a small signal MOSFET with a max. avg. Drain current of 350 mA and way too high RDSon. In your circuit the avg. Drain current is > 500 mA, overloading the transistor.
    Use a power MOSFET, see e.g. the test jig for the LT3757A that is supplied with LTSPICE.
    upload_2021-7-28_11-6-44.png
     
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