Steve Thompson wrote:
>
>
>-----Original Message-----
>From: Ian White, G3SEK <G3SEK@ifwtech.com>
>To: amps@contesting.com <amps@contesting.com>
To: <amps@contesting.com>
>Date: 16 May 2001 13:04
>Subject: Re: [AMPS] Voltage Doublers
>
>
>>
>>Glenn McNeil wrote:
>>>
>>>A few questions about voltage doublers. I'm building a single tube 4CX250R
>for
>>>70cm using a voltage doubler
>>>supply. This is my first attempt at FWD supplies.
>>>
>>>I have a transformer with about 750vac secondary, 12ohms dc resistance.
>I'm
>>>planning on using IN5408 diodes and
>>>a string of electro's.
>>>
>>In one word, DON'T. The secondary resistance of the transformer -
>>combined with the effects of primary resistance and diode on-resistance,
>>which you also need to factor in - will ruin the voltage regulation.
>Are you being a bit harsh on the transformer here, Ian? 12 ohms strikes me
>as quite low.
>
Yes, but that's only the secondary. Perhaps I should have mentioned
this, but in order to get the *total* effective series resistance, you
need to add in the resistance of the primary plus the mains wiring, all
multiplied by N-squared where N is the step-up turns ratio; and then add
the resistance of the rectifier string (I * number of diodes * voltage-
drop). It's very likely that the contribution from the primary will
double the effective resistance of the transformer.
>Assuming a total source resistance of 50 ohms,
I see you've added at least some of those contributions...
>simulation with 2 x 100uF
>caps shows 1.2A rms in the transformer, 800mA rms in the caps and 66V ripple
>at 300mA dc. Doesn't seem too unreasonable to me
What does the voltage regulation look like, from 'zero' current (bleeder
resistors only) to say 100mA ZSAC and then to 300mA peak?
What diode model did you use... and can you e-mail it please?
>but I'd agree with you that
>it's well worth breadboarding it before committing to metalwork.
Absolutely! The difficulty is to find a way of loading it for testing,
unless you already have another amp that you can wire across to. Safety
is also a big issue here.
73 from Ian G3SEK Editor, 'The VHF/UHF DX Book'
'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.com/g3sek
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