Re: solid state coil problem

To: "'Tesla List'" <tesla-at-poodle.pupman-dot-com>
Subject: Re: solid state coil problem
From: Tesla List <tesla-at-stic-dot-net>
Date: Thu, 13 Nov 1997 10:21:29 -0600
Approved: tesla-at-stic-dot-net

From:	RODERICK MAXWELL [SMTP:tank-at-mail.magnolia-dot-net]
Sent:	Wednesday, November 12, 1997 7:12 PM
To:	Tesla List
Subject:	Re: solid state coil problem

Thank you for your reply. This my second shot at building a smp so
don,t be to hard on me! My fist attempt was a flyback converter running
at about 500khz but was very underpowered.

"What voltage parameters did you design it work within?"
 
 The primary voltage will probably be 160vdc maximum since I'm not going
to use a split power supply. I have 20,000uf worth of filter caps in in
the power supply rectified by a 1kv, 35amp, bridge. I am using a variac
to control the circuit, and to prevent current surge caused by the high
capacitance filter. I probably have to much filter but I want to ensure
that there will be low ripple even at high current draw.
  
  ???? Is it?  You need to check your bias and/or drive scheme.

   You may be right. The circuit does not seem to turn on until power
supply voltage reaches 20vdc. I am using a simple series pass transistor
voltage regulator to power the signal generator circuit. Apparently I
should change the resistor in the regulator for a lower value so the
transistor will switch on at a lower voltage.
  
  The core that I'm using is not ferrite but iron powder. It has a much
higher frequency response than ferrite (over 1Mhz) but a much lower
inductance per turn. I tried to compensate for this by ordering the
largest core I could find in this material (type 26)
  The reason for wanting higher freq. response is I would like to use a
small secondary.

  Since I last posted this problem I have come up with at least a
partial solution to the problem. I will parallel two or more transistors
on each leg of the primary to compensate for the current draw, and the
increased heating caused by higher freq. and higher primary voltages.
Since this will call for more drive power for the switching transistors
I will use a much more powerfull driver. A HV400MJ/883 made by Harris.
It is able (from the information on the web site ) to source 6amps, and
sink 30amps at 300khz!
 This enables it to switch 10,000 pf loads! Of course since I,m using a
pushpull design I,ll need two.

  Did you use magnetic design technics on this?

       Nope.

                                 Frankensteins Helper
                                         Max