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I have tried a PFC Boost simulation with lt1242. The specification is Input Voltage Range = 90 to 264 Vac, Output Voltage = 400 Vdc. I have got the result but I am not sure does this make sense at all or what to verify else. If anybody give some feedback rearding this it would be great. I have attached the ss of my simulation circuit, input and output voltage waveforms, output voltage and output current waveforms, input voltage and input current waveform. [enter image description here]

[enter image description here]

[Input Voltage and Input Current waveform]

1: [enter image description here]

4: [enter image description here]

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  • \$\begingroup\$ "am not sure does this make sense at all or what to verify else" What are the requirements? Does it meet those? \$\endgroup\$
    – winny
    Commented Aug 2, 2023 at 13:22
  • \$\begingroup\$ You need to plot input voltage and input current together and, try and plot on a white background and name your nodes please. \$\endgroup\$
    – Andy aka
    Commented Aug 2, 2023 at 13:42
  • \$\begingroup\$ Hi, I added this in the post. kindly please check it. I found input current is not sinusoidal with voltage. \$\endgroup\$ Commented Aug 2, 2023 at 14:33
  • \$\begingroup\$ Can you post a screen capture with Vin and Iin (AC) not showing the massive inrush? Steady-state. White background, again. \$\endgroup\$ Commented Aug 2, 2023 at 14:47
  • \$\begingroup\$ As the output voltage is above the set point, input current will drop to near zero. 2 kohm @ 400 V is only 80 W and most PFCs won’t have very sinusodial current at very light load. Given your 2800 uF capacitor, I’d assume you plan to load this in the kW-range? \$\endgroup\$
    – winny
    Commented Aug 2, 2023 at 15:12

1 Answer 1

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  • V5 is a sine source. It's voltage is entered as peak, not peak-peak or RMS. RMS to peak is RMS x 1.414. So 120VAC = sine(0 170 60), and 240VAC = sine(0 340 50).
  • You have a bridge, to an 800µH inductor, to a massive 2800µF capacitor. What current is that inductor rated for? What is the max surge current rating of the capacitor? At \$t_0\$ that capacitor will be discharged and current could be hundreds of Amperes. Will the components survive the turn-on inrush current? This is always a concern with PFCs. Inrush current is very high, and using lower mains voltage does not help because when the PFC starts operating, it has to then boost the low output voltage, consuming even more input current as quickly as possible.
  • Run the simulation with sources zeroed at \$t_0\$. There is a setting in the .tran 30m options, right-click it. Then it starts the simulation with everything discharged, and you'll then see this large inrush current and the LT1242 startup.
  • The usual solution to limiting inrush current is physically large PTC thermistor(s). These are normally a low value (such as 10Ω) placed in series with the incoming AC power. At inrush, they warm up and their value increases to say 200Ω or so, limiting the current. Moments later, they cool, and their value returns to 10Ω.
  • PTC thermistors have the added benefit of slightly reducing EMI backfed into the mains. Will want to use an EMI filter before the PFC to "catch" the noise it generates, else that noise could affect other devices nearby.
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  • \$\begingroup\$ "The usual solution" does not seem to be a good solution when used on grids that are not as stable as North America or EU. The need for two relays (one with a series resistor) really comes into effect. \$\endgroup\$ Commented Aug 2, 2023 at 14:50

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