Will this blow my choke to pieces?

[hayden123]

Hi,

Just a quick question...I'm trying to design a power supply for a DC darling so need about 400V B+ @ 55mA. I have a power transformer that is rated at 400VAC, 150mA but has multiple primary options (200, 220, 230 and 250V). I thought that maybe a pseudo choke input using the 200V tap with a 230V mains voltage to get 460VAC on the secondary.

However, my one concern is for the choke which is rated at 150mA and I'm wondering whether it would survive the inrush current which is close to 1A. Would this design work or is it just too much inrush?

Any help would be appreciated. See attached picture for what I'm talking about.

[AndrewT]

What is your "normal" mains voltage? 230Vac, 235Vac, 240Vac, 245Vac?
Use the correct primary tapping to match your "normal" voltage.

using a lower voltage tapping on a higher voltage supply will take your transformer towards saturation. That will waste electricity and unfortunately that extra electricity leads to overheating of the transformer. More than 10% mismatch in supply voltage and you will severely heat your transformer.
That's why you have a mix of 4% and 8% tapping gaps.

[DF96]

Yes, the choke will be fine. No, as AndrewT says, using the wrong primary tap could cause saturation. Most 'domestic' mains transformers are designed to be on the verge of saturation when used off-load at their rated input voltage.

[metalsculptor]

If you don't mind making a bit of heat you could use a bridge rectifier with a choke input filter to get around 750V (use two 450V caps in series for the filter) then regulate it down to 400V that should give around 20W dissipation in a series pass regulator.

You need to make sure that the minimum current required for the choke is used or the input voltage will head for 1Kv at light load, you have the simulator to test it with, just rearrange a few components and add two diodes.

[hayden123]

Aah I see. Did not realise that would occur with the primaries. My mains voltage is 230VAC. So would I see the same effect if I used a higher primary tap in order to obtain a lower-than-rated voltage for a CLC filter? I'm assuming so. Will work with 400VAC then and see what I can come up with.

[AndrewT]

Hi,
at rated voltage the transformer gives out rated current without overheating and maintains long term reliability.

At greater than rated voltage, the transformer runs hotter. That may have consequences, but does not guarantee failure.

At less than rated voltage the transformer runs cooler but is still limited to the same rated current. This is equivalent to saying that the VA has gone down in proportion to the drop in Vac.