I am trying to build a 260V input mains circuit for a 36V output and 25W Power. I have calculated the required Resistance, Capacitor, and Inductance, I have got the required results. However, I am required to make a closed-loop PWM. Could anybody please help? Thanks! enter image description here PS: I am very new to LT Spice and Power Electronics.

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    \$\begingroup\$ That 260 V sine source is delivering 260 V peak. Did you want 260 V rms? 'Not getting' is not a good problem description. What output ARE you getting? 0 V, 1 MV? \$\endgroup\$ – Neil_UK Oct 2 '20 at 15:29
  • \$\begingroup\$ Sorry for that vague question I am getting 130uV. No I wanted 260 peak. \$\endgroup\$ – Subhransu Sekhar Bhattacharya Oct 2 '20 at 15:49
  • \$\begingroup\$ What becomes 130 uV? Aux? Vin? Is S1 conducting at all? \$\endgroup\$ – winny Oct 2 '20 at 15:56
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    \$\begingroup\$ Please reconsider the idea of building an un-isolated mains supply. \$\endgroup\$ – Chris Stratton Oct 2 '20 at 17:33
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    \$\begingroup\$ I suggest opening the .asc file in a text editor and copy/pasting the text into a code block within your question. That way we can troubleshoot the actual circuit instead of making assumptions based on a screenshot with limited information. Regardless, the main thing that sticks out at me is V5 should be a B-source and not a V-source. \$\endgroup\$ – Ste Kulov Oct 3 '20 at 2:42

I think there will be some problem with the calculation. For this to work without regulation, two things must be met.

1- The duty cycle of the switch signal is fixed.

ON time = 36 x K

OFF time = (260-36) x K ;(K = constant)

2- A minimum of inductance is required for the current of the inductance to be continuous. That is, it cannot be decreased to zero during the switch off time.Here we choose either inductance or frequency. One defines the other. egy


The output capacitor only affects the ripple of the output signal. Its value is not critical.

I don't know where the 90 uH came from, it can't be ruled out in principle, but in practice it would require too high switching frequency.

  • \$\begingroup\$ I am allowed to use a regulation circuit but I cannot figure out the criterions. \$\endgroup\$ – Subhransu Sekhar Bhattacharya Oct 3 '20 at 14:09
  • \$\begingroup\$ I have figured out all the criterions but the average output doesnt meet the requirement as I have not been able to put in regulation. Thus I had to use the Duty cycle as a fixed value. \$\endgroup\$ – Subhransu Sekhar Bhattacharya Oct 3 '20 at 14:16
  • \$\begingroup\$ The 11V / us slew rate is likely to be very low here. Maybe a high speed comparator would be better than an operational amplifier. \$\endgroup\$ – csabahu Oct 4 '20 at 23:20

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