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Very High Voltage Piezoelectric Power Supply - Digitaly Variable - Lightweight SMT

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Uriah

Tue Aug 07 2007, 04:16AM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

Many thanks to everyone who has added to this thread. It has ALL been extreamly helpfull.

I am so busy lately that I ushualy only get to do computer work a few times a week.

Acquiring a new type of Piezoelectric Transformers will enable my power supply to put out more then twice the Wattage (16W), at only half the weight of the previously considered unit. Attached is the basic HV layout. I am using push pull topography to ensure stable operation of the PT. The pulse transformer will be made by CustomCoils with a MEMs cooling unit connected to the coil and HV component array using a complex ceramic heat sink.

As to application, is it ok to talk about Electrohydrodynamics, i.e. "lifters" on this forum?

As to power source, 3100mAh LiPoly will power my brushless powered RC airplane for 10 minutes above 30amps at 11.1V. With the new PTs the max input voltage is 12.5V and the MAX ouput it 3.15kV at 8watts. Also, in my design the cooling devices enhance the Piezoelectric/ dielectric performance.

With this much energy I have managed to keep most of the aircraft the exact scale I was already planning. But now I have more than twice the pre-calculated aerodynamic modification. The chord of the wing and some other features of the aircraft will change with energy density per unit volume of surrounding atmosphere.

Like I said previously, I will share a lot more about my project when this stage is tested. I'll have my website up by then and I invite all who care to join my in discussion there.

Best regards,
Uriah George

P.S.
In the attached render not all the SMD components are visible and most of the circuit design is not drawn in.

...

Tue Aug 07 2007, 06:23AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

If you are worried about size/weight, I would dump the BS2 and use a strait PIC (you can even get one that has parallax'es interpreter burned in them, just add resonator, eeprom, and power).

Also, I would be a tiny bit worried about having these vary large/fast pulses right next to the microprocessor...

Uriah

Thu Aug 30 2007, 12:58AM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

Hey everyone! My prototype is going very well. I have the IGBT, and all the SMD components for its driving circuit. I have the Multi-layer PTs, (100 of them!) and am still working on its driving circuit.

Can someone help me out. I need to find a sine wave (sinusoidal) generator that is SMD and can opperate at 47kHz Â±1.5kHz, fixed or fully variable. I found this one from Frequency Devices Inc.

It actualy would work perfect, electricaly. It has a precise frequency control option (Â±1.5kHz) which is good for tunning the MTP's resonant frequency.

BUT IT IS HUGE FOR MY APPLICATION NEEDS!!!

If anyone can help me find a smaller SMD oscillator device or cicuit it would be very helpfull.

The MPT's exact specs are as follow:

Efficiency (at resonant frequency): 96%
Output current max: 9.4mA
Output voltage max: 3.46kV p-p (WHAT DOES p-p MEAN???)
Input voltage (less then or equal to): 12V
Input current max: 1510mA
Static input capacitance (1kHz 1Vrms): 215nF Â± 10nF
Operation temp range -20 ~ 70Â°C
150KÎ© load resistance (25Â°C Î»/2 sine wave, resonant)
Voltage step-up ratio (resonant): 100 Â±5

The specified control and test layout is attached along with the equivalent circuit for the PT.

Regards,
Uriah George

...

Thu Aug 30 2007, 01:51AM

Registered Member #56 Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445

Sounds good... p-p means peak to peak, ie if you looked at the output on a scope and measured the voltage from the peak to the trough of the sine wave, that would be 3.5kV. More practically, if you use a fullwave rectifier you will also get about 3.5kV.

As to a smaller oscillator, why not just make a discrete transistor oscillator? If you used decent quality components (ie 1%) you should be able to keep it nice and stable...

Uriah

Thu Aug 30 2007, 02:19AM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

So a transistor oscillator could be controlled by a digital potentiometer using slow on-off code from my BS2px? Because switching it on and off directly would produce squarewave, this needs to be a uniform sine wave.

Regards, Uriah

Steve Conner

Thu Aug 30 2007, 08:45AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

If you really want a stable sinewave of adjustable frequency, I can think of two ways to do it: a state-variable oscillator, or a DDS. The DDS is probably more compact, and can be programmed digitally: see the Analog Devices AD9835 chip as an example:

But, surely the whole point of piezo transformers is that they can be wired to self-oscillate in a simple circuit. If you want to control power, maybe you should study the techniques used for dimming CCFL backlights powered by piezo transformers, since CCFL backlighting is their main application, after all.

I bet there is an all-in-one driver chip somewhere that takes brightness commands digitally, and if you could get 100 custom piezo transformers, you should be able to get samples of those too.

thedatastream

Thu Aug 30 2007, 01:15PM

Registered Member #505 Joined: Sun Nov 19 2006, 06:42PM
Location: Yorkshire!
Posts: 329

Once you load a Piezo transformer they de-Q like any resonant circuit and the need to control the frequency exactly reduces.

Also, each device will have a tolerance associated with it so setting up this supply for one specific Piezo might not work for another. Some kind of frequency measurement to provide a feedback loop is a good idea...

Conundrum

Fri Aug 31 2007, 10:26PM

Registered Member #96 Joined: Thu Feb 09 2006, 05:37PM
Location: CI, Earth
Posts: 4061

Hi..

I did wonder about using these with the piezo outputs in series separated by diodes, but the primaries in parallel.

You would still require a method of isolating the primaries but this could be done with a single multi-winding ferrite coil.

:)
(I doubt that putting 25KV+ on a transformer designed for 3kv would be a good idea)
-A

Uriah

Mon Sept 03 2007, 09:00AM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

Thank you everyone! I spent an hour looking up some of the suggestions, and now I really know I have my work cut out for me.

I am hopefully moving to California very soon to begin college and work for an aerospace LLC there. A lot of my career will revolve around HV electronics. I guess you could say this project is a pre-curser to what will come there, but still expectations are high.

I'll get to everyone here in three weeks with a PDF of the final design.

And NO, you can't hook the PTs in series.... but you can build your own to get to that voltage. They are elegantly simple devices to construct!

Attached is a picture I took of one of the Multi-layer Piezoelectric Transformers from China.

Best regards,
Uriah

Uriah

Mon Sept 03 2007, 09:06PM

Registered Member #898 Joined: Sun Jul 15 2007, 07:50AM
Location:
Posts: 20

P.S. Here is another picture showing the other side which has two plastic mounting pads with a layer of foam inbetween. That is actualy just my assumption, I am guessing they are ment to be glued to mounting surface. The layer of foam makes it so that as little vibration as possible from the PT is transferred to the PCB.

1188853560 898 FT28407 Mpt3610b10l1 Foam Pads

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