PSUD2 question: how do I sim an LCLCL filter?

[ckniker]

I am trying to simulate an LCLCL filter in Duncan Amp's PSUD but can't seem to add an Inductor to the circuit in anything except as an LC pair. As a result, I can't add the final L to my filter....

I'm not experienced in PSU design enough to know if there's a good reason for this....


Thanks in advance,
Chris

[BobEllis]

How about making the final capacitor as close to 0 as PSUD will allow? I don't have it installed at the moment, but if you enter .001n does the program accept it?

Why would you want an inductor output filter? That pretty much kills your hf performance.

[ckniker]

Yes, I was able to "get around" the limitation by choosing a small C value. There's still an impact due to the capacitor's resistance component, however. I guess I'll have to bite the bullet and learn Spice if I want to analyze the impact before building it...

Why would you want an inductor output filter? That pretty much kills your hf performance.

I'm a still-learning newbie so I don't understand why it would kill the high frequency response. i.e. Why would the additional capacitor prevent a loss in hf?

BTW, this filter is being used as a filament supply to a DHT that i'm using as a learning tool.

[BobEllis]

Set the capacitor ESR at several megohms and you shouldn't see any appreciable effect.

When making a voltage source you want to make its output impedance low. The inductor output will make the high frequency impedance high. Any hf noise induced on the power supply lines won't be attenuated. Assuming that your heater has a low impedance path to ground it shouldn't be much of an issue, but generally a capacitive output filter is preferred.

Also, note that with an inductive input to your filter you will need a higher voltage transformer than you would with a capacitive input filter. It may be a practical issue depending on availability of suitable transformers.