LTspice AC/DC convertor

[mading2018]

325V @ 4A = 1300W.
1300W / 400V = 3.25 A.
400V / 3.25A = 123 Ω.

I see, but is it correct to use 325.27 (peak value)? Or i mean, is it correct to use 230 V (RMS) as well and do the same calculations?

Like this:
P=u*I = 230 *4 = 920 W
I = 920/400 =2.3 A
R=400/2.3 = 174 ohm

What value do you think that I should in the voltage source? 325.27 or 230 V ?
I think 325.27 should be okay, since I have put that value in the amplitude and that will give 230 V (RMS).

 

[alec_t]

but is it correct to use 325.27 (peak value)? Or i mean, is it correct to use 230 V (RMS) as well and do the same calculations?

It depends if you're wanting to limit peak current or RMS current.

 

[mading2018]

I want to limit the RMS current.

 

[alec_t]

Then use 230V as the input voltage for the calculation.

 

[mading2018]

Okay, 230 V (RMS) for the calculations, and 325.27 V (for the simulation, which gives 230 V (RMS). Just to make it clear what I am doing.

Do you how to change the switching frequency to 150 kHz? I think that I should you use this equation:

f_c = 1/(2 pi R C)

in order to calculate the values for C3 or R12 at the DCM.
What I understand from the LT8312 document, f_c needs to be lower than 12 Hz.

However, the time period of the output of one waveform period is always 10ms, so it means that I have 100 Hz as switching freq, even tough I tried to change the C3 and R12.

Could you please try to modify my file to see if you can obtain a higher frequency?
Thank you alec_t.

 

[alec_t]

Do you how to change the switching frequency to 150 kHz?

No. The LT8312 doesn't use a fixed oscillation frequency. It operates in the 'critical conduction mode' with a varying frequency which is load dependent and is a result of the power factor correction method that the IC uses.

 

[mading2018]

Do you think its better to use the LT1249 instead? Its operating for 100 kHz fixed, but I can maybe assume its "close enough" to 150 kHz.

 

[alec_t]

Why are you determined to use 150kHz?

 

[mading2018]

Cause I need to reduce the component size in my design. The old design had 100 kHz, so that's why I need to increase the frequency.

 

[ronsimpson]

component size

The inductor? What other components?

 

[mading2018]

Mainly the inductors and capacitors. Its a request that the charger should be light weighted as much as possible.

 

[mading2018]

Why are you determined to use 150kHz?

I noticed now there is LT1248, (up to 300 kHz), but there is no standard demo for it. I need to save time, in order to finish the simulation ..

 

[alec_t]

but there is no standard demo for it

Yes there is.

 

[mading2018]

Thank you, I have missed that!
Do you know how to change the switching frequency for that IC?

 

[alec_t]

The resistor and capacitor on the Rset and Cset pins determine the oscillation frequency.

 

[mading2018]

The resistor and capacitor on the Rset and Cset pins determine the oscillation frequency.

Yes I noticed that, thank you. I have selected 150 kHz. Alec_t, could you please check my LT1248 circuit? I think it works now.

 

[alec_t]

It works, but whether or not the component values are optimised for a 50Hz mains input and your chosen output voltage, I don't know.

 

[mading2018]

If you really have to do interleaved in SPICE, and there are no ICs in SPICE, then use a Linear.com part and:
1) connect MOSFET like normal.
2) IC output ---(5uS delay)---Gate of second MOSFET.
This is not perfect but almost does interleaved.

I think I understand your suggestion, and yes, I agree with you that the interleaved do not need to be perfect.
I tried with LT1249, with 100 kHz internally in the IC-circuit, and I put a delay on the voltage source to connected to VCVS circuit.
The output looks okay, but I think the PFC doesn't work properly, since there is current spikes in the input. Maybe it is something with the switching parameters that needs to be adjusted?

 

[alec_t]

The gate drive arrangement to Q2 is wrong. Q2 source is floating. Try using a BV device with the 'delay' function.

 

[mading2018]

The gate drive arrangement to Q2 is wrong. Q2 source is floating. Try using a BV device with the 'delay' function.

You mean like this? or should I remove the whole VCVS circuit. What do you mean Q2 is floating? Is there something missing in the connections?