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Boost Converter Simulation With LT1242 or LT246 PWM Controller


Hi, my name is Nebi. I am a hardware design engineer. I am working on a boost converter. My converter parameter is as follows.

Vin_min=20 VDC, Vin_max=31 VDC, Vout=75 VDC, Pout=2500 W and frequency=150kHz

I made simulations with LT1242 and LT1246 PWM Controllers in LtSpice. But I have some questions.

The simulation circuit and waveform graph are as follows. In the LT1246 simulation, the Mosfet PWM signal is intermittent. Something is resetting. I changed sense resistor but did not solve this problem. What could be causing this situation?


I set up the same circuit for LT1242. A similar reset situation happened here. If sense resistor value is not correct, how can I calculate this resistor value?


In addition, I did not find LTpowerCAD model for LT1242 and LT1246. Therefore I could not loop compensation. How can you help with this? Could it be that the output voltage is incorrect because my compensation values are wrong?

Thanks for be interest.

Have a nice day!

  • Hi Nebi,

    I check your circuit, LTspice wise, i did not find an issue with the simulation, parameters, etc. however we need to make sure if all conditions are with specs to verify if the problem is related to an issue of this specific model itself. I forward your concern to our Application Engineering team to help you in checking those stuffs. In case an issue is indeed confirm, there will be steps needed to be done and it will take some time to resolve the problem.

    Thank you.



  • HI Nebi,

    I received a response from the apps engineering team. Base on their assessment, this is not a spice issue either, which was what I thought at first but rather, the 2500W load is just too much for this model. A typical application in datasheet on a offline supply application is only at 30W and LT1242 is not designed to drive large FET or parallel FET to support large current.

    You may what to try looking for the suitable part for your design. Please also note to always check the datasheet for its operating region as each models are only designed to operate with the boundary of its specification.



  • Hi PaulDaria,

    Firstly, thanks for response. And then, do you have any suggestion as suitable controller for our given design parameters previously.

    Vin_min=20 VDC, Vin_max=31 VDC, Vout=75 VDC, Pout=2500 W and frequency=150kHz

    Secondly, I consider how much power we can transmit on boost topology as maximum with a single circuit. 


  • Hi NIsik445,

    Please check our part LT8551. You should have more freedom to do higher power boost converter.

    There is a demo board if you want to have a reference design. 

    Please use LTpowerCAD. It should help you about how much power you can get on a single-channel boost. You can find articles and references in datasheets too about computations.