----- Original Message -----
From: "Ian White, G3SEK" <G3SEK@ifwtech.com>
To: <amps@contesting.com>
Sent: Wednesday, May 16, 2001 1:16 PM
Subject: Re: [AMPS] Voltage Doublers
>
> 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.
>
How about a bunch of standard light bulbs in series?
> 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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