[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: SSTC questions



Original poster: "Terry Fritz" <twftesla-at-qwest-dot-net>

Hi Jan,

There are a number of configurations for a solid state Tesla coil.  But it
sounds like you are using a H-bridge at the coil's resonant frequency to
drive a primary.

I drive my solid state coil with an RF power supply in this configuration:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/CWCoil/CWDig.jpg

The power supply has a 50 ohm output and can read off forward and reflected
power.  I find that I can tune 50 ohms fairly well by varying the
frequency.  There is information on the output impedance at:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/CWCoil/CWImpedance.txt

Also a bunch of pictures and stuff at:

http://hot-streamer-dot-com/TeslaCoils/MyCoils/CWCoil/

I really didn't think much about impedances when I made it but I worried
more about getting the coil to tune within the frequency range of the power
supply.  A ferrite core transformer could be used to tune the input
impedance.  My power supply has a build in multi tapped load match
transformer but I just use the 50 ohm output.

I don't have a primary cap or anything so there is no real stored energy to
be punched back into the supply.  It is a well protected plasma supply
anyway but, aside from high reflected power when it is not tuned, the load
seems very tame.

Hope this helps and hope I was not too far off :-)

Cheers,

	Terry

At 01:59 PM 8/4/2001 +0300, you wrote:
>Hi,
>
>some questions about SSTCs, again. ;o) It's about a full-bridge SMPS.
>
>1) which impedances must be matched, really? someone said that all
>should be matched. Does that mean
> a) estimated streamer load input impedance
> => b) secondary output impedance
> => c) secondary unloaded base impedance
> => d) step-up transformer output impedance
> => e) driver input impedance (Uin_min^2/Pin)
>
>This seems like quite much... Ok a) and b) probably will match
>themselves "automatically". But for the designing part, wouldn't it be
>enough to just match unloaded TC base input Z to the driver input Z
>with that step-up transformer?
>
>I figure that the transformer output Z should be equal to the TC base
>input Z, right? 
>
>The other option would be narrowband 1/4wave transformer, i.e.
>T1_out_Z = SQRT ( Z_pri_in * Z_TC_in ). Intuition tells this might be
>the better way.
>
>It'd be a big help if some SSTC-gurus could comment on which method is
>the correct one?
>
>
>2) for a full-bridge, how do I calc the necessary commutating diodes'
>current handling capability, repetetive-pulsed, for the case when a
>large amount of the stored energy from the secondary is reflected back
>into the driver primary side?
>
>3) primary current: the peak (sinusoidal) current is probably equal to
>the (square-wave) peak flat-top current?
>
>3) when the worst happens and considerable stored energy is reflected
>back to the driver primary and tries to charge the main storage
>capacitors, should there be some sort of overvoltage protection
>accross the step-up transformer primary winding? Like MOVs/VDRs? Or kW
>transient suppressors? Anyone found this to be necessary?
>
>
>Many thanks!
>
>cheers,
> - Jan
>