Sorry, actually the power requirement is very low. ..1ma is what I meant to say. Also the input voltage isn't a critical requirement either. Vin can be anywhere from
10V to 50V
Why piezo? 1. Less radiated RF 2. A standard CCFL has to much capacitance between the windings and the core to achieve the level of floatingness I desire. (sure floatingness is a word!, really) :-)
Why that frequency? Much easier to filter. In fact, I had already goosed up a standard CCFL inverter to 380Khz and was pleased to discover that at that frequency little or no filtration seemed to be required at all for my relatively high impedance adjacent circuitry.
toss
tap.
2KV
Interesting. Thanks for the tip. When I goosed up my CCFL inverter made by TDK, I got piss poor output which I assumed was due to core losses. Perhaps I'll dork around with it some more and try your suggestions and see what I get.
However, I still want the output to be floating more so than I'll probably be able to obtain with a hotrodded magnetic xfrmr. But at least it'll get me in the game until I can locate a USA supplier for a 168kHz piezo which AFAIK is about the peak frequency being made to date. Hopefully that'll be high enough to solve the induced noise problem
You expect a chunk of ceramic to handle two watts or so?? Why piezo, and why that frequency? Use a standard CCFL transformer (Cooper/Bussman comes to mind), toss the Royer design; use low Rds(on) FETs with a driver and bypass the tap. Drive near output resonance frequency; at 10meg load i got over 2KV pk-pk and resonance was roughly 250-300KHz.
Thanks, yes, I have already considered the battery option at least for now in the experimental phase of this project. Also have considered using a a low voltage low frequency piezo inverter in place of the battery to supply power to and float a high frequency-hotrodded magnetic CCFL inverter
and not
So far, the highest resonant frequency I've seen for piezo CCFL type transformers is in the neighborhood of 160-170kHz. Do you think this is an upper boundry inherent in the material? Anyone know ?
On 17 Apr 2005 05:29:11 -0700, "Martin Davis" wroth:
A magnetic inverter or a normal piezo device powered from a completely separate battery should be able to achive an extremely high degree of floatability. A rechargable battery isolated with a relay to allow recharging when the device is connected to a power source but nominally "off", should be do-able.
Piezo devices are usually operated at a resonant point in their response. That's why the choice of operating frequencies is limited and not adjustable.
Just curious... what don't you like about the Royer design? Jim Williams seems to have done an awfully good job advocating its usage (although I realize his classic app note is now pushing something like a decade old).
On 17 Apr 2005 15:51:02 -0700, "Martin Davis" wroth:
The piezo elements have to get thinner as their resonant frequency goes up. Perhaps there is a point where the element gets too thin to support the voltage required. A thinner element might also be less able to withstand the heat generated. The efficiency can't be 100%. At least some heat is generated within the element.
Perhaps he was shunning the Royer for my purposes which for now is to jack up the operating frequency of an old magnetic CCFL inverter.
I wasn't able to stabilize the operation at any whimsically chosen abitrary frequency. Regardless of how I tried to tune the Royer circuit, it seemed to favor 84kHz or 385kHz.
It would be a flip of the coin which of these two states it would come up in when power was applied.
Rather than try to resolve this problem and since I needed to get more power anyway, I finally did pretty much as he said and tossed the Royer in favor of an externally clocked control circuit with beefier chippers
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