Power transformer with DC offset

[thunderdan]

G'day,

First post here I'm new and after a quick brows through the content this seems like a good forum.

I need to test a circuits ability to withstand a ripple voltage (±7V from a 0.5R source, 50Hz - 200kHz, from MIL-STD-1275). From about 20kHz - 300kHz I want to use an amplifier (special purpose 200W 10Hz - 500kHz 2R) and couple the AC on to the DC feed via a ferrite transformer. The DC to the equipment under test (EUT) is 28V@8A. The transformer would also transform the 2R output impedance to 0.5R.

Is this achievable with a transformer? I've built a number of ferrite power inductors so have some knowledge of how they work, however, am not sure how to design for the DC offset that will be present in secondary. From what I can tell this will cause the core to saturate.. Any tips?

Dan.

 

[Skogsgurra]

As you mention, DC saturation can become a problem.
Wouldn't it be possible to arrange a parallel path for the 20-300 kHz by using a DC block (film capacitor)?

Such a capacitor doesn't need to be huge. Not at those frequencies. A possible complication is the back-feed into the DC path.

Gunnar Englund

http://www.gke.org

--------------------------------------
Half full - Half empty? I don't mind. It's what in it that counts.

 

[thunderdan]

Thanks Skogsgurra,

I had thought of AC coupling with a cap, however the transformer was more to transform the impedance.. But that said.. a transformer to do the impedance transform then couple the AC with DC block cap. Can't believe I was complicating the issue so much! Seems this would be a suitable solution. I was planning on using a battery with a 0.5R source resistor.. So back feed shouldn't be problem.

Thanks for your input.