There is electrochromic film (which is some kind of capacitive load) that need to be driven with 50Hz alternating current, load voltage should be controlled in range 0-100V (with 8 or more fixed voltage levels or with continuous change in given range) by ARM processor with PWM or any other way.

Film segments of desired size have around 50KOhm impedance magnitude and should be driven by AC in order to function properly. Load power consupmtion is aproximately 0.001-0.01 watts at 100V.

I want to control many segments in parallel so per segment part of the circuit price and complexity are significant, so scheme with shared ac source design will be better.

The only idea i have for now is to produce low voltage alternating current with PWM and low pass filter and then use step up transformer to get high voltage output, but it looks over complicated for me and i'm not sure it will work at all.

  • \$\begingroup\$ Is the waveform critical? Or would a square(ish) or sawtooth(ish) wave do? Also, what is the load? \$\endgroup\$ – Anindo Ghosh Dec 28 '12 at 19:53
  • \$\begingroup\$ I have no idea about it, i'm sure it will work fine with simplified sinus, in fact i think that any symmetric waveform will be fine, not sure about sawtooth. The load is electrochromic film segment. \$\endgroup\$ – ETK Dec 28 '12 at 20:20
  • \$\begingroup\$ Can you use pulses as long as the average voltage is correct, or does it have to be a analog signal. A link to this "electrochromic film" stuff would help. What's it supposed to do when the proper signal is applied? What do you want it to do? \$\endgroup\$ – Olin Lathrop Dec 28 '12 at 20:21
  • \$\begingroup\$ youtube.com/watch?v=6qUc-x_DrHU - video with this film it's opacity controlled by voltage, when 100V applied film becomes transparent, lower the voltage applied - less transparent film will be \$\endgroup\$ – ETK Dec 28 '12 at 20:23

The load in question, from OP's clarification, appears to behave electrically almost like Electroluminiscent Sheet, or an EL panel, popular in LCD backlights and hobby / decorative applications: EL Sheet

Another popular form is EL Wire, with a similar principle of operation.

EL Sheet is easily driven using an "EL Inverter", either a special-purpose IC such as:

  • SuperTex HV853 High Voltage, Low Noise, Inductorless EL Lamp Driver
  • OnSemi MC33441 Electroluminescent Lamp Driver IC

... or using a flyback or step-up transformer based inverter design, as described in these articles:

The schematics in the above articles will give you an idea of the design elements involved, even if you don't want to lift a design outright.

Finally, you can also buy fairly inexpensive EL drivers / EL invertors, such as this $14.95 12 Volt wall-wart driven EL inverter from SparkFun:
SparkFun EL Inverter

EL Panel inverters are also available on eBay and other sites, often at much lower prices than the above. However, do make sure you understand how much capacitance the driver in question is designed for - and thus how much of the Electrochromatic Sheet can be driven by it. Larger pieces typically have higher capacitance hence more powerful / expensive inverters are needed.


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