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Re: DC power supply again


From: 	Harri Suomalainen[SMTP:haba-at-cc.hut.fi]
Sent: 	Thursday, September 04, 1997 6:36 AM
To: 	Tesla List
Subject: 	Re: DC power supply again

On Thu, 28 Aug 1997, Tesla List wrote:
> > Assume the gap fires, primary resonates and transfers only partially the
> > energy during 1st half cycle to the secundary. Then, the primary current
> > after resonance to 0 volts will start going partially to the cap (charging
> > it negative!) and partially through the flyback secundary and diode.
> > All the energy left in the cap (now negative) will have to be dissipated
> > somewhere. Possibility of distruction? Have you thought about this?
> 
> Indeed yes. I have already successfully run coils from such a supply. 

Humm.. very interesting. Does the gap quench after the 1st half cycle
(ie. when the cap has resonated to 0 volts) ? Have you checked that
perhaps? I find the reason making the system never loaded by a negatively
charged cap (after resonating) extremely important. It is the key to
keeping the device in working condition! (conserns about the second
setup below)

> The supply behaves like a current source of sorts and the gap shunts
> the output while conducting so the rectifiers need not hold off more
> than that required by the flyback design alone.

Humm.. Are you using a setup like this? This would seem the case you
are talking about, right?
                      cap
+hv ------+-----------||------)
          V                   )
          ^   <-gap           )
          |                   )
gnd ------+-------------------)  <-- primary

The problem I was talking about appears with a setup like this:
                gap
+hv -----+------><-------)
         |               )
         = cap           )
         |               )
gnd -----+---------------)  <- primary

Unfortunately I thought the thing narrowly and was thinking only about
the later type of primary circuit. Silly me.. :( At quick look the
second one seems to work properly in your type of setup.


> In fact using inductive storage is _exactly_ the right topology for 
> the job. You will instantly blow a forward or transformer type 
> converter if it has no current limiting and if it does, you are 

Certainly. I was all the time thinking on current limiting by perhaps
with a secundary choke (like in the normal forward topology) or by
some limiter in the primary side (like inductors in resonant topologies).

I'm not very fond of flybacks becouse they usually need larger
transformers. They also induce more stress to the primary switching
element(s). I'd go for some other topology but that's just me and
my personal preferances.

> likely to suffer serious gap quench problems. I have total confidence 
> in my choice based on experiments I have already conducted.

That is certainly great to hear. SMPSUs would certainly be nicer than
bulky polo bigs etc :) I'd just love to hear more on your findings as
your project advances more!

> I see simplicity as the best approach. I looked at multiple windings, 
> multiple transformers and it didn't look good. With good design, 
> switchers can be made pretty efficient with regard to heat 
> generation.

Yap, 90% (or even better!) is very realistic nowadays.
--
We have phone numbers already, why would we need IP-numbers! -unknown person

Harri.Suomalainen-at-hut.fi - PGP key available by fingering haba-at-alpha.hut.fi