LTspice smps diode simulation problems

[Mikezz]

Hi all,

I'v been messing around with designing a smps to charge a capacitor bank at 450v and a small current of around 77mA from an input voltage of 8.3 volts. My only problem now is that when I add a value to the diode on the output side of the circuit (D3) it adds voltage drops bellow 0 volts and spikes above 450v on each square wave.

The pictures attached bellow show a 'before' and 'after' of the output voltage. The 'before' picture (screenshot 4) is exactly what I need but any diode I try to use just produces the exact same weird drops and spikes on each wave (screenshot 3).

If anyone had an idea of why this was happening I would really love the help. Thank you!

 

[E-design]

It is called ideal vs real components. Ideal components provide ideal results while real components introduce all the unwanted inductances and capacitances that cause problems and losses.

It will get even worse if you model the transformer with a coupling coefficient less than one to include real leakage inductance.

 

[crutschow]

You are using a low frequency power-line rectifier for a high frequency signal. Such a diode has a lot of capacitance and slow recovery.
Change the diode to a Schottky type (no larger than you need).
You may still get some spikes, but they should be a lot lower.

 

[E-design]

I wasn't sure what a "uf" means in this case. Ultra-Fast?