[AMPS] Bridge vs. Doubler

Wed, 05 May 1999 15:21:40

Well, you're one up on me at this point Steve.  I haven't measured some of
the parameters to the degree you have, nor do I have SPICE for modelling.
My comments are based on somewhat theoretical calulations from a couple of
the few available (but well known in their field) books on transformer
design. One is by Reuben Lee and the other is by W. Flanagan.  Your model
for the doubler "seems" to predict peak secondary currents that "look" too
high.  Even the peak current for the FWB is alot higher than I'd expect,
except you've measured real values that agree fairly well.  I'll play
around abit to see if I can verify one way or 'tother.

Thanks...Phil
>
>Replying to the original, Phil VE3OZZ said
>
>>The rms current in each doubler diode is twice the DC load current, and the
>>peak secondary winding current is at least 2.8 times the DC load current.
>>This is why a transformer supplying a doubler circuit should be designed
>>for it.  It isn't enough to just look at the DC load current or the KVA
>>rating of the transformer when selecting one.  Knowing the wire size of
>>both windings is also a key piece of information.
>
>The whole piece was very well put but I disagree here. The measurements
>I have made to date stack up well with Spice simulations - here's what
>is predicted by Spice:
>
>The transformer model I used was chosen because I had transformers wound
>to this spec.
>
>1500V secondary, 40 ohms total (inc. primary allowance) eff. series
>resistance, bridge, 30uF smoothing and 3750 ohms load (560mA dc in
>load).
>
>The dc output is about 2100V average with a bit under 200V ripple. The
>peak current in the transformer secondary is 3.8A and the rms current is
>about 1.4A - 7 and 2.5 x the dc current respectively.
>
>I don't have an equivalent transformer designed for doubling so I made a
>guess for the model:
>
>750V secondary, 20 ohms total eff. series resistance, 2 diodes, 2 x 60uF
>in series smoothing, 3750 ohms load.
>
>dc output is 2000V average, a bit over 200V ripple. Peak current in the
>secondary is 5.5A, 10 x dc load current AND the conduction angle is
>longer by about 20%. I haven't done the rms calculation yet.
>
>>
>>Sorry for the diatribe, but there's my 2 cents worth.  Transformers are
>>more interesting than they look.
>
>And more difficult and much misunderstood.
>
>Steve
>
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